Rectifier TP5 reading way too high

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G-Man
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Rectifier TP5 reading way too high

Postby G-Man » Mon Jun 03, 2019 4:46 pm

An old client is asking me to troubleshoot their KISS machine. Has repro boards in it but not booting up. All rectifier voltages are good EXCEPT tp5 which is a whopping 63v Instead of the usual 43v.

I have checked the bridge rectifiers.

Any idea what could be causing such a high tp5 voltage?

Thanks.

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Toeckeder
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Re: Rectifier TP5 reading way too high

Postby Toeckeder » Mon Jun 03, 2019 6:55 pm

Speaking from experience, have you unplugged the sound board ?

Could be diode CR3 on the sound board. There is a power circuit there , input side of diode is 43v, other is 65v ish... if you read 65v each side, diode is blown and propagate 65v everywhere
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G-Man
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Re: Rectifier TP5 reading way too high

Postby G-Man » Mon Jun 03, 2019 7:04 pm

I “feel” like I have tried that, but I’ve been there 3 or 4 times and have started to lose track. But that is a good tip and something I will make sure I do when I go back this week.

Thanks

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Re: Rectifier TP5 reading way too high

Postby Toeckeder » Mon Jun 03, 2019 7:16 pm

Keep us informed please !

I had exactly that on my Playboy, was not getting the 7th flash because voltage was 63v caused by CR3.

The source problem was an idiot (me) testing the sound board without screws to secure it... it felt and generated a big spark. I was lucky to only blow a .02$ diode and found the issue quickly.
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G-Man
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Re: Rectifier TP5 reading way too high

Postby G-Man » Tue Jun 04, 2019 2:03 pm

Well, I went back to the KISS machine, disconnected the sound board and unfortunately there is still 63V at TP5.

Just for kicks, I threw in an entire transformer/rectifier assembly and still had 60V at TP5. So that should eliminate the problem being either the transformer or rectifier.

If the sound board doesn't appear to be the problem, what other possibilities are there ?

Inquiring minds want to know. :)

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Toeckeder
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Re: Rectifier TP5 reading way too high

Postby Toeckeder » Wed Jun 05, 2019 4:20 pm

Have you disconnect J1 J3 at the rectifier?

That would left only the cabinet coils... knocker, coin reject.. short with something else in the cabinet?

Maybe remove J2 pin 2 as well for a quick test?
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Vid: DIY MAME, TEMPEST, NUCLEUS CANNON
Gone: Punch-Out!!, TARGET ALPHA, STARGATE, SPIRIT OF 76, ROLLERGAMES, TAXI, TOMMY, EARTHSHAKER, BACK TO THE FUTURE, TWILIGHT ZONE, TX SECTOR, CENTAUR, AC/DC PRO, ROLLERGAMES, WHIRLWIND, TIME MACHINE, GALAGA, GRAND LIZARD, TORPEDO ALLEY, F-14 TOMCAT, BLACKOUT, ALGAR

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Re: Rectifier TP5 reading way too high

Postby sylvain » Wed Jun 05, 2019 6:09 pm

There is not much else apart than a leaky or shorted diode CR3 on the sound board that can jack-up TP5 from 43V to 63VDC I think.
This is due to the C17 filtering capacitor on the sound board - when CR3 is bad, which smooths the rectified pulsing voltage
to higher flatter RMS voltage value, and feeds it back through the bad diode, towards the 43V solenoid voltage, and makes the MPU's
Zero Crossing Detector no longer seeing the pulses, thus not completing its 7th flash.

...Unless the transformer primary windings are incorrectly connected for 115/120VAC line in (too high secondary voltages),
or unless your meter does not read accurately pulsing rectified but not filtered voltage at TP5.

If this 63VDC was present for a while, this could have burned-out the zero-crossing detector 2K resistors (R113, R16 on an original MPU),
rendering the MPU not completing its 7th flash as well.

-Sylvain.
Looking for Bally Star-Jet, Capersville or The Wiggler, Williams Magic City, Grand Lizard, Swords of Fury, 1986 Pinstar Gamatron, and a few others.
Collecting & repairing electro-mechanical and solid state pinball machines with quality and care for over 35 years.
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Re: Rectifier TP5 reading way too high

Postby G-Man » Thu Jun 06, 2019 12:11 pm

Okay, thank you Toeckeder and Sylvain. At some point in my flurry of various attempts, I have definitely had J1 and J3 disconnected, but that may have been before I fixed some other voltage issues and now I am just obsessing over the TP5.
Part of the problem is I have always been limited in the amount of time I can spend troubleshooting the problem. But I am going back for a longer session soon.

The MPU is a repro board and I notice that it only gives me 3 flashes. When I put an original MPU back in, I am able to get 6 flashes. I figured that was because repro boards are a little less tolerant of incorrect voltages. But now the idea that the zero crossing circuit ( on both boards) have been compromised seems like a plausible one. I have the original MPU back in my possession and I will be putting it back into the Mystic game it came from tonight. I will be interested to see if it boots up in that game. If not, then the 2K resistors might just be the thing.

Will keep you posted. :)



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