Topic: Yet Another TNMT Repair Log  (Read 5167 times)

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Offline Womble

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Yet Another TNMT Repair Log
« on: April 30, 2012, 12:41:35 AM »
Picked up a faulty TMNT on ebay a month or so back...



...the seller had bought it as a faulty board but had never got round to looking at it.

The board was totally untouched, beyond the fact the EPROMs had been swapped to change the game version. There wasnt a non-original solder joint on the board, but it was stone dead. My work bench had been offline for a while so I had tested it in my JAMMA cabinet, and it was very dead, not even a pop from the speaker on power up just a blank screen.

Once I got it on the bench I fired it up again and got the same result. Measuring the voltages at the board showed I had 0v on the 12V line and 0.2v on the 5V line.

The edge connector was clean enough so the only likely reason for this was that something on the board was shorting out the PSU. My old arcade PSU which crapped out on me a while back used to make a ticking noise when it was shorted by a bad board, this one it seems doesnt give any signs at all.

I gave the board a once over eyeball check looking for twisted caps or bent pins making contact and found nothing so it was time to divide and conquer.

TMNT only uses +5v and+ 12v and a short on either one could shut the entire PSU down. So I unplugged the 12V feed from the PSU and powered it back up, the board leapt into life!



So only the 12V rail was shorted, the 12v doesnt go to many place on this board and the most likely candidate for the fault was the 1000uf 16v decoupling cap at C20 that sits between the 12v and ground.



It's tall, thin and sticks up well above the other components so it is often knocked off, or damaged. This one looked fine physically and the legs were not loose inside, but the resistance measurements between the 12V and ground JAMMA pins went crazy when it was touched. Surprisingly its ESR was fine, however an ESR meter doesn't actually measure resistance to come to up with the reading, it measures a harmonic ringing effect which it then bases a calculation on to get the ESR value; in this case the cap was totally hosed.

So it came off the board...



...and a replacement salvaged this morning from a scrapped chassis was ESR tested and installed.



The game now runs fine with sound, amazingly (for a PCB loaded with Fujitsu TTLs and old mask ROMS) there were no other faults at all. I ran the in-depth RAM/ROM check, it passed and the game runs perfectly.



Result - took me ten times longer to write this up and upload the photos than it did to fix it :)
Sic Transit Gloria Atari

Offline Panther

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Re: Yet Another TNMT Repair Log
« Reply #1 on: April 30, 2012, 11:53:39 AM »
Blimey that's got to be one of the quickest fixes in Womble history !!

Offline AndyRCM

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Re: Yet Another TNMT Repair Log
« Reply #2 on: April 30, 2012, 02:06:18 PM »
Nice one mate . . . very impressive (as always!) . . . :)
"I could see the faces of those who led pissing themselves laughing" - Funeral Pyre by The Jam

Offline billdooruk

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Re: Yet Another TNMT Repair Log
« Reply #3 on: May 01, 2012, 08:04:39 AM »
Yep....I'm impressed.

Another TMNT board saved  ;D

I will get one one day!!!!

Offline MaxHall

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Re: Yet Another TNMT Repair Log
« Reply #4 on: May 01, 2012, 02:00:31 PM »
impressive - well done!
Max Hall

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Offline Rog69

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Re: Yet Another TNMT Repair Log
« Reply #5 on: May 08, 2012, 07:24:25 AM »
I really enjoy reading these Womble but it depresses me to realise just how much of my electronic skills have gone by the wayside over the last 25 years of working since I studied electronics myself.

It's great to see someone doing component level diagnostics when everything is made so throw-away these days.


Offline AndyParkes

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Re: Yet Another TNMT Repair Log
« Reply #6 on: June 01, 2012, 10:55:11 AM »
I really enjoy reading these Womble but it depresses me to realise just how much of my electronic skills have gone by the wayside over the last 25 years of working since I studied electronics myself.

It's great to see someone doing component level diagnostics when everything is made so throw-away these days.



Would just like to echo this - always fascinating reading!

Offline Welgo

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Re: Yet Another TNMT Repair Log
« Reply #7 on: July 10, 2012, 03:20:18 PM »
A board with Konami ICs and a TMNT game is surely worth the repair ;)