stumped by WPC power driverboard

[Guest]

Archived from groups: rec.games.pinball (More info?)

Hi guys,
I was having a problem with my TZ resetting when holding both flippers.
Naturally the power driverboard was first to look @.
As I had a spare Funhouse with a perfectly looking board (very little
traces of heat etc etc) I decides to swap them as a quick test.

Resets remained.......

So I started to measure voltages.
Found out that the 9VAC was 8.5 VAC and this was due to the transformer
being jumpered @ 230 while wall voltage was 220.
So, I jumpered the game for 217V and the 9VAC was perfectly 9VAC now.

Resets remained........

So I measured the BR2 + side, on my meter it showed me 9VDC!
And as Marvin says it should be 12V (9VAC * root of 2 = approx 12V)

Sounds all clear as a whistle...
but, here is what I am stumped about.

I replaced the CPU board as it started to reset in attract mode as
well, with the 5V being picture perfect. I pressed on the CPU board and
the resets started again.
After this Swap the resets r gone.
But I am still left with the other readings from my multimeter than the
ones on Marvin's site.

And on top of that, all of my bridge rectifiers outputs r not what the
theory should say they should be (AC*root2=DC)
My MultiMeter is RMS.
So I started to look with a scope.
All looks fine there, and correspond with my DMM (Digital Multi Meter)
Peak is 10V, ripple is approx 2V
I see no sign of a broken diode on the sopes output.

So questions r.
How can I get 9V and Marvin 12?
Why r all my rectifiers outputs too low when calculated with the
AC*root2=DC formula?

Is Marvin perhaps reading peak voltage or something????

Hope hearing from you guys soon.
Thanx!

 

[Guest]

Archived from groups: rec.games.pinball (More info?)

2V ripple is too much. Replace the capacitor (c5 I think)

 

[martin]

Archived from groups: rec.games.pinball (More info?)

measurements and meters can be a bit off. Most meters get the AC RMS
right, but can strugge with the DC ripple. As you saw on your scope,
the DC side has a peak of 10V (I'll explain that in a moment) and a
ripple of 2V. Your meter did OK by approximating that as 9V. If you
disconnect the 5V loads, you'll see the voltage float up closer to that
12V number as the ripple will go away and the diode forwad voltage drop
will reduce.

OK so heres the maths:

9V a.c. = 9* (root 2) peak to peak = 9*1.414 = 12.726V

But that's peak to peak. To get to DC, we have to rectify the AC with
diodes.

Under load, a typical diode has a voltage drop of 1.2V. there are two
diodes in the circuit at any time, so the measured output voltage peak,
under load, would be 12.73 - (2*1.2) = 10.33V.

If there is a minimal load, the Vf of the diodes drops to maybe 300mV.
So the capacitor can get back up to 12V.

 

[martin]

Archived from groups: rec.games.pinball (More info?)

That's a perfectly feasible value if the CPU and other boards are not
connected.

 

[martin]

Archived from groups: rec.games.pinball (More info?)

Did some more arithmetic. A 15,000uF capacitor in a circuit delivering
1.7A at a nominal 11V will indeed show about a 2V ripple on the scope.
Deteriorating capacitors will cause a relatively rapid increase in the
ripple voltage, there's a square law involved.

 

[martin]

Archived from groups: rec.games.pinball (More info?)

Looks fine to me. It is possible that your capacitor needs replacing,
but as the resets are gone I would not mess with it.

If you want to see the Marvin numbers, try disconnecting the power to
the CPU board. The scoped ripple on the cap should just about
disappear.

You do need a true RMS meter to measure the ripple on the cap.

 

[Guest]

Archived from groups: rec.games.pinball (More info?)

I myself am not that worried over a ripple of 2V (tt)@ the current that
is drawn.
But how do you measure the ripple normally?
My RMS gives on AC a ripple of 250mV and the scope clearly shows 2V.
So, the DMM messes up here.
Following the repair guide from Marvin I should use the DMM.

Did you use a scope on the BR2's output or a DMM?

On 2005-09-12 22:58:02 +0200, "seymour-shabow@excite.com"
<seymour-shabow@excite.com> said:

> 2V ripple is too much. Replace the capacitor (c5 I think)

 

[Guest]

Archived from groups: rec.games.pinball (More info?)

I completely agree on your theory,
But then how can Marvin measure 12.7 V there?
http://pinrepair.com/wpc/tstbrig2.jpg

Thats what I am most puzzled about.
What is wrong? Our theory or the measurement from Marvin.
He uses a normal DMM (fluke 83) and I a True RMS (fluke 87)

thanx for thinking this over

On 2005-09-12 23:02:44 +0200, "martin" <martin.reynolds@gmail.com> said:

> measurements and meters can be a bit off. Most meters get the AC RMS
> right, but can strugge with the DC ripple. As you saw on your scope,
> the DC side has a peak of 10V (I'll explain that in a moment) and a
> ripple of 2V. Your meter did OK by approximating that as 9V. If you
> disconnect the 5V loads, you'll see the voltage float up closer to that
> 12V number as the ripple will go away and the diode forwad voltage drop
> will reduce.
>
> OK so heres the maths:
>
> 9V a.c. = 9* (root 2) peak to peak = 9*1.414 = 12.726V
>
> But that's peak to peak. To get to DC, we have to rectify the AC with
> diodes.
>
> Under load, a typical diode has a voltage drop of 1.2V. there are two
> diodes in the circuit at any time, so the measured output voltage peak,
> under load, would be 12.73 - (2*1.2) = 10.33V.
>
> If there is a minimal load, the Vf of the diodes drops to maybe 300mV.
> So the capacitor can get back up to 12V.

 

[Guest]

Archived from groups: rec.games.pinball (More info?)

ok, so you think my powerboards r just fine too ?

Thanx!

On 2005-09-13 00:37:23 +0200, "martin" <martin.reynolds@gmail.com> said:

> That's a perfectly feasible value if the CPU and other boards are not
> connected.

 

[Guest]

Archived from groups: rec.games.pinball (More info?)

On 2005-09-12 13:51:26 -0700, FrEnZy said:

> Hi guys,
> I was having a problem with my TZ resetting when holding both flippers.
> Naturally the power driverboard was first to look @.
> As I had a spare Funhouse with a perfectly looking board (very little
> traces of heat etc etc) I decides to swap them as a quick test.
>
> Resets remained.......
>
> So I started to measure voltages.
> Found out that the 9VAC was 8.5 VAC and this was due to the transformer
> being jumpered @ 230 while wall voltage was 220.
> So, I jumpered the game for 217V and the 9VAC was perfectly 9VAC now.
>
> Resets remained........
>
> So I measured the BR2 + side, on my meter it showed me 9VDC!
> And as Marvin says it should be 12V (9VAC * root of 2 = approx 12V)
>
> Sounds all clear as a whistle...
> but, here is what I am stumped about.
>
> I replaced the CPU board as it started to reset in attract mode as
> well, with the 5V being picture perfect. I pressed on the CPU board and
> the resets started again.
> After this Swap the resets r gone.
> But I am still left with the other readings from my multimeter than the
> ones on Marvin's site.
>
> And on top of that, all of my bridge rectifiers outputs r not what the
> theory should say they should be (AC*root2=DC)
> My MultiMeter is RMS.
> So I started to look with a scope.
> All looks fine there, and correspond with my DMM (Digital Multi Meter)
> Peak is 10V, ripple is approx 2V
> I see no sign of a broken diode on the sopes output.
>
> So questions r.
> How can I get 9V and Marvin 12?
> Why r all my rectifiers outputs too low when calculated with the
> AC*root2=DC formula?
>
> Is Marvin perhaps reading peak voltage or something????
>
> Hope hearing from you guys soon.
> Thanx!

Another procedure for checking WPC power -
http://www.flippers.com/will-tips.html#Thermistor

I do have some new pictures to show what I am talking about, and the
test can now be run while the board is installed in the game. simply
stated, you can use a 3A diode to see if the bridge rectifier is
failing under load WITHOUT removing it first (and possible damaging the
PCB).

Oh, and check that the connector to J101 is not showing signs of
overheating, this will cause a voltage drop and reset issues as a
result!

John :-#)#
--
(Please post followups or tech enquires to the newsgroup) John's
Jukes Ltd. 2343 Main St., Vancouver, BC, Canada V5T 3C9 Call
(604)872-5757 or Fax 872-2010 (Pinballs, Jukes, Video Games)
www.flippers.com "Old pinballers never die, they
just flip out."

 

[Guest]

Archived from groups: rec.games.pinball (More info?)

Thank you for your technical insights on this!

On 2005-09-13 06:23:04 +0200, "martin" <martin.reynolds@gmail.com> said:

> Did some more arithmetic. A 15,000uF capacitor in a circuit delivering
> 1.7A at a nominal 11V will indeed show about a 2V ripple on the scope.
> Deteriorating capacitors will cause a relatively rapid increase in the
> ripple voltage, there's a square law involved.