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Pioneer amp SA-930 no output, what causes?

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Anonymous
September 24, 2004 9:04:09 PM

Archived from groups: rec.audio.tech (More info?)

Thanks for the idea of a blown fuse. Not the cause. there's one fuse
inside the unit. it looks good. the unit lights up and gets hot. just no
output. elsewhere online I saw an idea of a faulty "main amplifier IC"
but when looking at this unit, I see two identical ICs with many legs
mounted on the floor plane...I assume one is for each channel...since my
problem affects both channels, I do not believe one of those ICs is the
problem. any other ideas?!!



> > yesterday the old amplifier was working fine. today, it lights up in
> > front...it gets hot... but no sound is output. neither channel.
problem is
> > not my phonograph nor is it the speakers. anyone know what typically
causes
> > an amp to suddenly stop output? the unit is 17 years old.
>
> Some ideas:
>
> Could be a blown fuse. Some home audio gear sometimes has fuses
> inside, if you don't see a fuse holder on the back panel. Remember to
> unplug the amp from your wall socket and wait a few minutes before
> tinkering with anything!

More about : pioneer amp 930 output

Anonymous
September 24, 2004 9:04:10 PM

Archived from groups: rec.audio.tech (More info?)

In article <csY4d.108090$D%.39273@attbi_s51>, jay heldman
<jayboydog@eudoramail.com> wrote:

> Thanks for the idea of a blown fuse. Not the cause. there's one fuse
> inside the unit. it looks good. the unit lights up and gets hot. just no
> output. elsewhere online I saw an idea of a faulty "main amplifier IC"
> but when looking at this unit, I see two identical ICs with many legs
> mounted on the floor plane...I assume one is for each channel...since my
> problem affects both channels, I do not believe one of those ICs is the
> problem. any other ideas?!!

Is this an integrated amp? Some have main-out/pre-in jacks on the
back that use little wire jumpers to connect the pre-amp to the
power amp. Make sure that those are in place if you need them.
Also, check over all the possible switches that would affect this,
like tape monitor and effects loop switches.

If you have another amp, connect the tape out, and later, the pre-out
to an aux input on a known good system. Then connect a tuner, tape,
or cd to your bad amp. See if you get output at the pre-amp level.

Next, try this in reverse. Connect a device with a variable output
level to the main-in on your SA-930. Make sure the output level is
at zero when you start. Gradually turn up the output level. If
you get nothing out of the speakers, then your amp really is bad.

A common problem with power amps is the shutdown circuit. If it
has a relay, check it to see if it is bad. Look for additional
fuses. Check to make sure there are no wire fragments or metalic
dust that is shorting out the wiring, the speaker connectors, or
the circuit board. Finally, look for any variable controls on
the circuit board. You may have some DC voltage making it to the
the speaker outputs. One of these controls might be able to adjust
the DC offset to fix that (you likely need a service manaul to
know how to adjust it).

Beyond that, you need a scope to start tracing out the audio
path to see where your sound is getting lost.

-john-

--
====================================================================
John A. Weeks III 952-432-2708 john@johnweeks.com
Newave Communications http://www.johnweeks.com
====================================================================
Anonymous
September 26, 2004 1:32:13 AM

Archived from groups: rec.audio.tech (More info?)

mid 1980s amplifier. no builtin tuner. the unit is relatively heavy so I
assume it has some good quality stuff inside!
no output volume. unit lights up, gets hot.
I do not know about pre-amp, this is simply a unit which has four input
slots (phono, tuner, cd, aux/vid) and tape deck input/output. there are two
speaker channels A, B each having right and left channel (no surround, no
5.1)

I assume something on the board is broken... there is one interesting
component on the board which sticks up and has a transparent cover,,,it
looks as though it has a copper coil inside. without my giving the part
number of this transparent covered thingy, maybe this thingy is what is
broken! I don't know how to scope anything, nor do I have the tools! but,
if the unit gets hot and does light up, what part of the process can we
assume is working? I notice when switching input selection, sometimes
there's a slight lighting of the volume signal indicator. when the unit was
working fine, the dual channel volume signal indicators would dance
right-to-left with different sound output. I doubt I would pay much to have
the unit professionally serviced, but if I knew which part was broken, I
might buy a replacement part and try installing it myself! thanks for your
ideas!


> > Thanks for the idea of a blown fuse. Not the cause. there's one fuse
> > inside the unit. it looks good. the unit lights up and gets hot. just
no
> > output. elsewhere online I saw an idea of a faulty "main amplifier IC"
> > but when looking at this unit, I see two identical ICs with many legs
> > mounted on the floor plane...I assume one is for each channel...since my
> > problem affects both channels, I do not believe one of those ICs is the
> > problem. any other ideas?!!
>
> Is this an integrated amp?
> A common problem with power amps is the shutdown circuit. If it
> has a relay, check it to see if it is bad. Look for additional
> fuses. Finally, look for any variable controls on
> the circuit board. You may have some DC voltage making it to the
> the speaker outputs. One of these controls might be able to adjust
> the DC offset to fix that (you likely need a service manaul to
> know how to adjust it).
>
> Beyond that, you need a scope to start tracing out the audio
> path to see where your sound is getting lost.
>
> -john-
>
> --
> ====================================================================
> John A. Weeks III 952-432-2708 john@johnweeks.com
> Newave Communications http://www.johnweeks.com
> ====================================================================
Related resources
Anonymous
September 30, 2004 1:21:55 AM

Archived from groups: rec.audio.tech (More info?)

The transparent plastic cased object is the speaker protection relay
probably (or the main power rail switching). It should click in 5 seconds
after powering on - unless there is a fault condition such as a failed amp
output where high DC voltages are sent out and would otherwise damage your
speakers.

You say there are 2 large black plastic modules with 10-16 pins? probably
with STK xxx on them. Its most likely that one of these has failed.
You ideally need to establish which has failed- its unlikely both have. Is 1
getting hotter quicker? this is probably the dud.
Now If you've no experience on electronics I can't condone you trying to
replace this yourself- you need to unsolder it, check for other failed parts
nearby etc and check the new one is running stably.
Take it to a techy really
Hope this helps
Andrew
Anonymous
October 1, 2004 4:37:18 AM

Archived from groups: rec.audio.tech (More info?)

yes. the transparent plastic covered object looks to be a mechanical
switch labled "TYPE AP4U, 24V DC, ASR 102-0 131" I do not hear or see
anything transitioning after the unit is powered on. maybe this relay is
broken? or maybe the dc voltages are too high which would mean something
before the relay is needing repair? do I grasp indication of the unit's
problem by the relay not switching ?

as for the two semiconductor chips (twenty legs each) on the floor plane,
neither gets hot. Each one is labled PA4008 245AC


mid 1980s amplifier. no built-in tuner. the unit is relatively heavy so I
assume it has some good quality stuff inside!
no output volume. unit lights up, gets hot.
I do not know about pre-amp, this is simply a unit which has four input
slots (phono, tuner, cd, aux/vid) and tape deck input/output. there are two
speaker channels A, B each having right and left output (no surround, no
5.1)


"JVC dude" <wilkinsons.hifi@talk21.com> wrote in message
news:415b195e$0$17963$ed2619ec@ptn-nntp-reader02.plus.net...
> The transparent plastic cased object is the speaker protection relay
> probably (or the main power rail switching). It should click in 5 seconds
> after powering on - unless there is a fault condition such as a failed amp
> output where high DC voltages are sent out and would otherwise damage your
> speakers.
>
> You say there are 2 large black plastic modules with 10-16 pins? probably
> with STK xxx on them. Its most likely that one of these has failed.
> You ideally need to establish which has failed- its unlikely both have. Is
1
> getting hotter quicker? this is probably the dud.
> Now If you've no experience on electronics I can't condone you trying to
> replace this yourself- you need to unsolder it, check for other failed
parts
> nearby etc and check the new one is running stably.
> Take it to a techy really
> Hope this helps
> Andrew
>
>
Anonymous
October 1, 2004 4:46:45 AM

Archived from groups: rec.audio.tech (More info?)

here's a paragraph someone seemingly smart writes online,
source=http://experts.about.com/q/1749/3551382.htm:
The reason it shuts down is because of excessive current drain, thus
tripping the protection circuit and opening the relay feeding the outputs.

The output transistors (mounted on heatsinks) is the likely cause. You will
have to replace them.

This is 80 to 90% of cause for failure in audio amplifiers.

Make sure you know how to do it; they are critical for proper mounting and
heat transfer.


"JVC dude" <wilkinsons.hifi@talk21.com> wrote in message
news:415b195e$0$17963$ed2619ec@ptn-nntp-reader02.plus.net...
> The transparent plastic cased object is the speaker protection relay
> probably (or the main power rail switching). It should click in 5 seconds
> after powering on - unless there is a fault condition such as a failed amp
> output where high DC voltages are sent out and would otherwise damage your
> speakers.
>
> You say there are 2 large black plastic modules with 10-16 pins? probably
> with STK xxx on them. Its most likely that one of these has failed.
> You ideally need to establish which has failed- its unlikely both have. Is
1
> getting hotter quicker? this is probably the dud.
> Now If you've no experience on electronics I can't condone you trying to
> replace this yourself- you need to unsolder it, check for other failed
parts
> nearby etc and check the new one is running stably.
> Take it to a techy really
> Hope this helps
> Andrew
>
>
Anonymous
October 1, 2004 9:14:02 AM

Archived from groups: rec.audio.tech (More info?)

I am not sure of the terminology involved, but there is a metal object
(running the width of the amp) with metal radiators on it. attached to the
underneath side of this object are four things each having three legs which
insert to plugs on the floor plane. of the four things, two are
green -labeled 2SA1075, and two are black -labeled 2SC2525. Each of the
four things has the letters O, Z, (G) near the three legs.

are these things the output transistors mentioned below? if they are, does
just one go bad? or are all four replaced at the same time? is the metal
object having the radiator fins called the "main rail" and/or "heatsync"?


> here's a paragraph someone seemingly smart writes online,
> source=http://experts.about.com/q/1749/3551382.htm:
> The reason it shuts down is because of excessive current drain, thus
> tripping the protection circuit and opening the relay feeding the outputs.
>
> The output transistors (mounted on heatsinks) is the likely cause. You
will
> have to replace them.
>
> This is 80 to 90% of cause for failure in audio amplifiers.
>
> Make sure you know how to do it; they are critical for proper mounting and
> heat transfer.
>
>
> "JVC dude" <wilkinsons.hifi@talk21.com> wrote in message
> news:415b195e$0$17963$ed2619ec@ptn-nntp-reader02.plus.net...
> > The transparent plastic cased object is the speaker protection relay
> > probably (or the main power rail switching). It should click in 5
seconds
> > after powering on - unless there is a fault condition such as a failed
amp
> > output where high DC voltages are sent out and would otherwise damage
your
> > speakers.
> >
> > You say there are 2 large black plastic modules with 10-16 pins?
probably
> > with STK xxx on them. Its most likely that one of these has failed.
> > You ideally need to establish which has failed- its unlikely both have.
Is
> 1
> > getting hotter quicker? this is probably the dud.
> > Now If you've no experience on electronics I can't condone you trying to
> > replace this yourself- you need to unsolder it, check for other failed
> parts
> > nearby etc and check the new one is running stably.
> > Take it to a techy really
> > Hope this helps
> > Andrew
> >
> >
>
>
Anonymous
October 1, 2004 1:42:27 PM

Archived from groups: rec.audio.tech (More info?)

yes those 2SA, 2SC devices are the output transistors, the black Ics you
referred to, are something else.

What is getting hot? the main alloy heatsink? back to my orig post, can you
identify where the heat is coming from?

the source you quote does have some relation to your fault, but excessive
current isn't the only way to 'open the relay', a DC offset on the output
due to a failed o/p transistor will do the same.

I still advise against having a go yourself, but 2 o/ps are for left
channel, the other 2 for the right. its likely only 1 channel is duff.
Normally we would replace the 2 from 1 channel as a pair sine you can't tell
whether one may be weakened by the other failing.
as a test you may try carefully and without shorting any 2 metal points
together, using a voltmeter with the black wire to metal sub
chassis/heatsink, see if you can measure a high voltage, say +50v or -50v on
the middle of the 3 legs of the rectangular white ceramic resistor pack with
the red probe. Set the meter to above 50 volts DC range- ideally a digital
meter. the resistors are1 inch wide 1/4" thck, 3/4" high with 0.22 ohms
(omega symbol) on them

if you can't measure and voltage on either then your fault is probably
elsewhere, but I suspect you will measure a high (rail) voltage

Once again, if you don't know what you're doing don't try it, theres some
high voltages knocking around and its easy to short together 2 metal
contacts and make yourself a nice smoke generator.

As someone put it the other day, all the magic blue smoke is released
from the transistors!

good luck
AW
Anonymous
October 2, 2004 6:39:53 AM

Archived from groups: rec.audio.tech (More info?)

being careful not to short any two legs, attached voltmeter to the center
leg of ceramic resistor packs labeled RGC55 0.47ohms KX2 2D. Facing the
unit from the front and reaching inside, the resistor pack on right reads
20V, the resistor pack on left reads zero. The metal heat sync seems to be
warmer on the right side (as viewed from in front and reaching inside) with
the outside (black -labeled 2SC2525) seeming to be generating most heat.

what might one conclude based on the left resistor pack reading no voltage,
right resistor pack reading 20V, and seeming more heat generated by right
side ??

Thank you.


"JVC Dude" <wilkinsons.hifi@talk21.com> wrote in message
news:7E97d.476$QQ1.181@newsfe3-gui.ntli.net...
> yes those 2SA, 2SC devices are the output transistors, the black Ics you
> referred to, are something else.
>
> What is getting hot? the main alloy heatsink? back to my orig post, can
you
> identify where the heat is coming from?
>
> the source you quote does have some relation to your fault, but excessive
> current isn't the only way to 'open the relay', a DC offset on the output
> due to a failed o/p transistor will do the same.
>
> I still advise against having a go yourself, but 2 o/ps are for left
> channel, the other 2 for the right. its likely only 1 channel is duff.
> Normally we would replace the 2 from 1 channel as a pair sine you can't
tell
> whether one may be weakened by the other failing.
> as a test you may try carefully and without shorting any 2 metal points
> together, using a voltmeter with the black wire to metal sub
> chassis/heatsink, see if you can measure a high voltage, say +50v or -50v
on
> the middle of the 3 legs of the rectangular white ceramic resistor pack
with
> the red probe. Set the meter to above 50 volts DC range- ideally a digital
> meter. the resistors are1 inch wide 1/4" thck, 3/4" high with 0.22 ohms
> (omega symbol) on them
>
> if you can't measure and voltage on either then your fault is probably
> elsewhere, but I suspect you will measure a high (rail) voltage
>
> Once again, if you don't know what you're doing don't try it, theres some
> high voltages knocking around and its easy to short together 2 metal
> contacts and make yourself a nice smoke generator.
>
> As someone put it the other day, all the magic blue smoke is released
> from the transistors!
>
> good luck
> AW
>
>
Anonymous
October 2, 2004 9:38:20 AM

Archived from groups: rec.audio.tech (More info?)

One would conclude the problem is on the channel where that 20 volts was
measured. Probably that output IC, though there could be another problem.
Solder connections, a bad resistor or capacitor, etc.

Mark Z.


"jay heldman" <jayboydog@eudoramail.com> wrote in message
news:Zxo7d.159257$D%.83519@attbi_s51...
> being careful not to short any two legs, attached voltmeter to the center
> leg of ceramic resistor packs labeled RGC55 0.47ohms KX2 2D. Facing the
> unit from the front and reaching inside, the resistor pack on right reads
> 20V, the resistor pack on left reads zero. The metal heat sync seems to
> be
> warmer on the right side (as viewed from in front and reaching inside)
> with
> the outside (black -labeled 2SC2525) seeming to be generating most heat.
>
> what might one conclude based on the left resistor pack reading no
> voltage,
> right resistor pack reading 20V, and seeming more heat generated by right
> side ??
>
> Thank you.
>
>
> "JVC Dude" <wilkinsons.hifi@talk21.com> wrote in message
> news:7E97d.476$QQ1.181@newsfe3-gui.ntli.net...
>> yes those 2SA, 2SC devices are the output transistors, the black Ics
>> you
>> referred to, are something else.
>>
>> What is getting hot? the main alloy heatsink? back to my orig post, can
> you
>> identify where the heat is coming from?
>>
>> the source you quote does have some relation to your fault, but
>> excessive
>> current isn't the only way to 'open the relay', a DC offset on the output
>> due to a failed o/p transistor will do the same.
>>
>> I still advise against having a go yourself, but 2 o/ps are for left
>> channel, the other 2 for the right. its likely only 1 channel is duff.
>> Normally we would replace the 2 from 1 channel as a pair sine you can't
> tell
>> whether one may be weakened by the other failing.
>> as a test you may try carefully and without shorting any 2 metal points
>> together, using a voltmeter with the black wire to metal sub
>> chassis/heatsink, see if you can measure a high voltage, say +50v or -50v
> on
>> the middle of the 3 legs of the rectangular white ceramic resistor pack
> with
>> the red probe. Set the meter to above 50 volts DC range- ideally a
>> digital
>> meter. the resistors are1 inch wide 1/4" thck, 3/4" high with 0.22
>> ohms
>> (omega symbol) on them
>>
>> if you can't measure and voltage on either then your fault is probably
>> elsewhere, but I suspect you will measure a high (rail) voltage
>>
>> Once again, if you don't know what you're doing don't try it, theres some
>> high voltages knocking around and its easy to short together 2 metal
>> contacts and make yourself a nice smoke generator.
>>
>> As someone put it the other day, all the magic blue smoke is released
>> from the transistors!
>>
>> good luck
>> AW
>>
>>
>
>
Anonymous
October 2, 2004 10:46:42 PM

Archived from groups: rec.audio.tech (More info?)

not sure I have identified output IC. underneath the metal heatsync, which
runs across the width of the amp, are four o/p transistors (3 legs each).
how would one test the transistor to determine its status? is any of these
o/p transistors also known as o/p IC?

of the 4 o/p transistors, two are black -labeled 2SC2525, and two are
green -labeled 2SC2525

so, are these transistors also called IC? and how to verify one is fault?
would one of the o/p transistor (being bad by itself) cause the amp's output
to speakers to be none?

Thank you.



"Mark D. Zacharias" <mzacharias@yis.us> wrote in message
news:2s7eopF1h68voU1@uni-berlin.de...
> One would conclude the problem is on the channel where that 20 volts was
> measured. Probably that output IC, though there could be another problem.
> Solder connections, a bad resistor or capacitor, etc.
>
> Mark Z.
>
>
> "jay heldman" <jayboydog@eudoramail.com> wrote in message
> news:Zxo7d.159257$D%.83519@attbi_s51...
> > being careful not to short any two legs, attached voltmeter to the
center
> > leg of ceramic resistor packs labeled RGC55 0.47ohms KX2 2D. Facing the
> > unit from the front and reaching inside, the resistor pack on right
reads
> > 20V, the resistor pack on left reads zero. The metal heat sync seems
to
> > be
> > warmer on the right side (as viewed from in front and reaching inside)
> > with
> > the outside (black -labeled 2SC2525) seeming to be generating most heat.
> >
> > what might one conclude based on the left resistor pack reading no
> > voltage,
> > right resistor pack reading 20V, and seeming more heat generated by
right
> > side ??
> >
> > Thank you.
> >
> >
> > "JVC Dude" <wilkinsons.hifi@talk21.com> wrote in message
> > news:7E97d.476$QQ1.181@newsfe3-gui.ntli.net...
> >> yes those 2SA, 2SC devices are the output transistors, the black Ics
> >> you
> >> referred to, are something else.
> >>
> >> What is getting hot? the main alloy heatsink? back to my orig post, can
> > you
> >> identify where the heat is coming from?
> >>
> >> the source you quote does have some relation to your fault, but
> >> excessive
> >> current isn't the only way to 'open the relay', a DC offset on the
output
> >> due to a failed o/p transistor will do the same.
> >>
> >> I still advise against having a go yourself, but 2 o/ps are for left
> >> channel, the other 2 for the right. its likely only 1 channel is duff.
> >> Normally we would replace the 2 from 1 channel as a pair sine you can't
> > tell
> >> whether one may be weakened by the other failing.
> >> as a test you may try carefully and without shorting any 2 metal
points
> >> together, using a voltmeter with the black wire to metal sub
> >> chassis/heatsink, see if you can measure a high voltage, say +50v
or -50v
> > on
> >> the middle of the 3 legs of the rectangular white ceramic resistor pack
> > with
> >> the red probe. Set the meter to above 50 volts DC range- ideally a
> >> digital
> >> meter. the resistors are1 inch wide 1/4" thck, 3/4" high with 0.22
> >> ohms
> >> (omega symbol) on them
> >>
> >> if you can't measure and voltage on either then your fault is probably
> >> elsewhere, but I suspect you will measure a high (rail) voltage
> >>
> >> Once again, if you don't know what you're doing don't try it, theres
some
> >> high voltages knocking around and its easy to short together 2 metal
> >> contacts and make yourself a nice smoke generator.
> >>
> >> As someone put it the other day, all the magic blue smoke is
released
> >> from the transistors!
> >>
> >> good luck
> >> AW
> >>
> >>
> >
> >
>
>
Anonymous
October 2, 2004 10:46:43 PM

Archived from groups: rec.audio.tech (More info?)

Sorry, thought I remembered output IC's from a previous post. Nevermind
that. The DC level you measured is still wrong for that channel, and is
associated with the two nearest output transistors (not IC's, sorry).

The transistors themselves are likely OK, since a failure there would
probably NOT give some intermediate voltage. I'd look for a bad resistor or
capacitor. More difficult if you're not a regular technician, but that's my
take on the situation.

Mark Z.


"jay heldman" <jayboydog@eudoramail.com> wrote in message
news:mIC7d.293585$mD.246346@attbi_s02...
> not sure I have identified output IC. underneath the metal heatsync,
> which
> runs across the width of the amp, are four o/p transistors (3 legs each).
> how would one test the transistor to determine its status? is any of
> these
> o/p transistors also known as o/p IC?
>
> of the 4 o/p transistors, two are black -labeled 2SC2525, and two are
> green -labeled 2SC2525
>
> so, are these transistors also called IC? and how to verify one is fault?
> would one of the o/p transistor (being bad by itself) cause the amp's
> output
> to speakers to be none?
>
> Thank you.
>
>
>
> "Mark D. Zacharias" <mzacharias@yis.us> wrote in message
> news:2s7eopF1h68voU1@uni-berlin.de...
>> One would conclude the problem is on the channel where that 20 volts was
>> measured. Probably that output IC, though there could be another problem.
>> Solder connections, a bad resistor or capacitor, etc.
>>
>> Mark Z.
>>
>>
>> "jay heldman" <jayboydog@eudoramail.com> wrote in message
>> news:Zxo7d.159257$D%.83519@attbi_s51...
>> > being careful not to short any two legs, attached voltmeter to the
> center
>> > leg of ceramic resistor packs labeled RGC55 0.47ohms KX2 2D. Facing
>> > the
>> > unit from the front and reaching inside, the resistor pack on right
> reads
>> > 20V, the resistor pack on left reads zero. The metal heat sync seems
> to
>> > be
>> > warmer on the right side (as viewed from in front and reaching inside)
>> > with
>> > the outside (black -labeled 2SC2525) seeming to be generating most
>> > heat.
>> >
>> > what might one conclude based on the left resistor pack reading no
>> > voltage,
>> > right resistor pack reading 20V, and seeming more heat generated by
> right
>> > side ??
>> >
>> > Thank you.
>> >
>> >
>> > "JVC Dude" <wilkinsons.hifi@talk21.com> wrote in message
>> > news:7E97d.476$QQ1.181@newsfe3-gui.ntli.net...
>> >> yes those 2SA, 2SC devices are the output transistors, the black Ics
>> >> you
>> >> referred to, are something else.
>> >>
>> >> What is getting hot? the main alloy heatsink? back to my orig post,
>> >> can
>> > you
>> >> identify where the heat is coming from?
>> >>
>> >> the source you quote does have some relation to your fault, but
>> >> excessive
>> >> current isn't the only way to 'open the relay', a DC offset on the
> output
>> >> due to a failed o/p transistor will do the same.
>> >>
>> >> I still advise against having a go yourself, but 2 o/ps are for left
>> >> channel, the other 2 for the right. its likely only 1 channel is duff.
>> >> Normally we would replace the 2 from 1 channel as a pair sine you
>> >> can't
>> > tell
>> >> whether one may be weakened by the other failing.
>> >> as a test you may try carefully and without shorting any 2 metal
> points
>> >> together, using a voltmeter with the black wire to metal sub
>> >> chassis/heatsink, see if you can measure a high voltage, say +50v
> or -50v
>> > on
>> >> the middle of the 3 legs of the rectangular white ceramic resistor
>> >> pack
>> > with
>> >> the red probe. Set the meter to above 50 volts DC range- ideally a
>> >> digital
>> >> meter. the resistors are1 inch wide 1/4" thck, 3/4" high with 0.22
>> >> ohms
>> >> (omega symbol) on them
>> >>
>> >> if you can't measure and voltage on either then your fault is probably
>> >> elsewhere, but I suspect you will measure a high (rail) voltage
>> >>
>> >> Once again, if you don't know what you're doing don't try it, theres
> some
>> >> high voltages knocking around and its easy to short together 2 metal
>> >> contacts and make yourself a nice smoke generator.
>> >>
>> >> As someone put it the other day, all the magic blue smoke is
> released
>> >> from the transistors!
>> >>
>> >> good luck
>> >> AW
>> >>
>> >>
>> >
>> >
>>
>>
>
>
Anonymous
October 4, 2004 12:52:41 AM

Archived from groups: rec.audio.tech (More info?)

anyone have another opinion?!! it lights up in
front...it gets hot... but no sound is output from either channel.

measured the middle leg voltage of the ceramic resistors....the right side
resistor measures 20volts and the o/p transistors mounted under the right
side of the heatsync get hot. while the left side resistor measures no
voltage and the o/p transistors under the left side of the heat sync do not
seem to get hot....

should I be able to recognize a broken component visually? how about
measuring voltage at any of the four test points accessable when the
heatsync is removed (and the 4 o/p transistors are lifted from their plugs
on floor plane)??

Thanks for all help!
Anonymous
October 7, 2004 1:59:21 AM

Archived from groups: rec.audio.tech (More info?)

Ok so you've established the right channel is running an offset.
As MArk suggests it may not be rail voltage 30-50v but an intermediate
voltage 20v you are measuring.(20v rails would mean a very low power amp!)
check this by measuring the voltage on the centre pins of the o/p tr'sw. one
will be +40v perhap, and the other -40v
If this is the case then yes the outputs are probably ok.
Also you can test the o/p tr's (unplugged this time) by looking for a short
across any 2 of the 3 pins. you will read some conductance across certain
junctions but we are most specifically looking for a short.
Assuming these are ok and that the rails are 40v plus then it really is just
a case of testing all other small transistors in that channel (6 or 7
nearby) looking for a short or (more difficult to identify) an open
junction.( not measuring like a diode - conducts one way, not the other).
I would not expect to find just a faulty cap or resistor without a blown
piece of silicon.
If you're going to solve this you need to learn about transistors and how to
measure them.
personally I always use an analogue meter/ on a low resistance range, and
one gets a feel for the readings (junctions on B-E B-C) (no junctions C-E)
(no reverse leaks) (PNP or NPN types)
A digital meter takes a long time to settle readings but does usually
have a diode range that can be useful.
It's here how us time served engineers earn our money- identifying
efficiently the dud bits and not replacing more than is really necessary.

Hope that helps for now.
Report back with your findings

AW
Anonymous
October 8, 2004 6:44:13 AM

Archived from groups: rec.audio.tech (More info?)

yes, i have an analog volt meter. to measure the voltage of center leg of
the o/p transistors which are attached under the heat sync, does one measure
the center leg to ground in similar manner as how one measured the voltage
of the ceramic resistors (middle leg to ground)?

i can use the ohm-meter to look for a short across any of the three legs of
the o/p transistors when I pull them from their plug on the floor plane of
the amp.

does it make sense to look for a burned mark on the other small transistors
in the faulty channel?

Thanks.


"JVC dude" <wilkinsons.hifi@talk21.com> wrote in message
news:41645cb4$0$54819$ed2619ec@ptn-nntp-reader01.plus.net...
> Ok so you've established the right channel is running an offset.
> As MArk suggests it may not be rail voltage 30-50v but an intermediate
> voltage 20v you are measuring.(20v rails would mean a very low power amp!)
> check this by measuring the voltage on the centre pins of the o/p tr'sw.
one
> will be +40v perhap, and the other -40v
> If this is the case then yes the outputs are probably ok.
> Also you can test the o/p tr's (unplugged this time) by looking for a
short
> across any 2 of the 3 pins. you will read some conductance across certain
> junctions but we are most specifically looking for a short.
> Assuming these are ok and that the rails are 40v plus then it really is
just
> a case of testing all other small transistors in that channel (6 or 7
> nearby) looking for a short or (more difficult to identify) an open
> junction.( not measuring like a diode - conducts one way, not the
other).
> I would not expect to find just a faulty cap or resistor without a blown
> piece of silicon.
> If you're going to solve this you need to learn about transistors and how
to
> measure them.
> personally I always use an analogue meter/ on a low resistance range, and
> one gets a feel for the readings (junctions on B-E B-C) (no junctions
C-E)
> (no reverse leaks) (PNP or NPN types)
> A digital meter takes a long time to settle readings but does usually
> have a diode range that can be useful.
> It's here how us time served engineers earn our money- identifying
> efficiently the dud bits and not replacing more than is really necessary.
>
> Hope that helps for now.
> Report back with your findings
>
> AW
>
>
Anonymous
October 8, 2004 10:46:19 AM

Archived from groups: rec.audio.tech (More info?)

It's not too likely you'll see any burn marks anywhere. You'll be looking
for things like a shorted junction on a small transistor, maybe a B-E short
on an output, though not likely, an open resistor, shorted capacitor, etc.

Mark Z.



"jay heldman" <jayboydog@eudoramail.com> wrote in message
news:1an9d.325281$mD.268779@attbi_s02...
> yes, i have an analog volt meter. to measure the voltage of center leg of
> the o/p transistors which are attached under the heat sync, does one
> measure
> the center leg to ground in similar manner as how one measured the voltage
> of the ceramic resistors (middle leg to ground)?
>
> i can use the ohm-meter to look for a short across any of the three legs
> of
> the o/p transistors when I pull them from their plug on the floor plane of
> the amp.
>
> does it make sense to look for a burned mark on the other small
> transistors
> in the faulty channel?
>
> Thanks.
>
>
> "JVC dude" <wilkinsons.hifi@talk21.com> wrote in message
> news:41645cb4$0$54819$ed2619ec@ptn-nntp-reader01.plus.net...
>> Ok so you've established the right channel is running an offset.
>> As MArk suggests it may not be rail voltage 30-50v but an intermediate
>> voltage 20v you are measuring.(20v rails would mean a very low power
>> amp!)
>> check this by measuring the voltage on the centre pins of the o/p tr'sw.
> one
>> will be +40v perhap, and the other -40v
>> If this is the case then yes the outputs are probably ok.
>> Also you can test the o/p tr's (unplugged this time) by looking for a
> short
>> across any 2 of the 3 pins. you will read some conductance across certain
>> junctions but we are most specifically looking for a short.
>> Assuming these are ok and that the rails are 40v plus then it really is
> just
>> a case of testing all other small transistors in that channel (6 or 7
>> nearby) looking for a short or (more difficult to identify) an open
>> junction.( not measuring like a diode - conducts one way, not the
> other).
>> I would not expect to find just a faulty cap or resistor without a blown
>> piece of silicon.
>> If you're going to solve this you need to learn about transistors and how
> to
>> measure them.
>> personally I always use an analogue meter/ on a low resistance range,
>> and
>> one gets a feel for the readings (junctions on B-E B-C) (no junctions
> C-E)
>> (no reverse leaks) (PNP or NPN types)
>> A digital meter takes a long time to settle readings but does usually
>> have a diode range that can be useful.
>> It's here how us time served engineers earn our money- identifying
>> efficiently the dud bits and not replacing more than is really necessary.
>>
>> Hope that helps for now.
>> Report back with your findings
>>
>> AW
>>
>>
>
>
!