Sucker for punishment - Stern MPU-100

[SPURR]

very very good work dude

[AskJacob]

Well, I'd better update even though it isn't very exciting so far.

Finally clicked that I have a bally -35 mpu, not a stern -100, but hey, there is not a huge difference, just surprised it never clicked with me (bally has "square" tracks, where the sterns are "organic" and curvy track). Funny how in your face it can be and you still just don't see it 

Anyway, she didn't boot. Now that is no real surprise, but still... I found 2 traces I marked down but forgot to repair, so did that. Lets see where we stand right now:

1 - LED jammed on, not even the flicker :(
2 - Reset works fine (needs some 'help' with the PC PSU I'm using as the reset circuit times out quicker than the PSU settles)
3 - CPU is certainly doing "something" - the data and address lines are cycling away, and the VMA is strobing
4 - can see activity on the ROM and RAM busses.

What I do know:

The PIAs and CPU and RAM are fine, a swap with known working parts gives the same symptoms.
My bench rig is fine, the working mpu-100 gives me the 6 flashes (the 7th needs 21v which I CBF setting up - besides if you get 6 you're sweet anyway :))

What I think it is:

It may be the bloody jumpers. Could they be more difficult and weirdly documented?

I may have missed a trace (likely!) - this needs a cool head, which I didn't really have at the time. You need to map out the schematic and probe your way around to make sure everything is connected. To ease the frustration, I moved on to strip the top of the Magic playfield, and rebuild the flippers in the IJ :)

Cheers
Jacob

[Strangeways]

To be expected ! This board will be a REAL challenge.

The jumpers must be correct for the ROMs you are using - if the jumpers are wrong, the board won't boot.

Eliminate the Reset section by shorting out pins 39 & 40 on the CPU.

My guess would be a short in the Address or Data lines. The U11 PIA would be where I would start. I have printout the schematic on an A3 page and work through all the permutations and combinations of the Address and Data lines.

[AskJacob]

Yah, thanks, sounds like I was heading in the right direction.

Part of me just wanted to hermit away until I sorted it out myself, so I could arise triumphantly and claim my solderhood...

But really, I spent a little too long on it during a busy week, and hit burnout - and thought if I front up, get another opinion then I may well get motivated to fix the damn thing 

Will remove the IC's, and probe out all the data lines. I have triple checked the jumpers, but will hit them with a "Fresh Head" in an evening or two. Fear not, this bugger is gonna run

Cheers
Jacob

[Strangeways]

Yah, thanks, sounds like I was heading in the right direction.

Part of me just wanted to hermit away until I sorted it out myself, so I could arise triumphantly and claim my solderhood...

But really, I spent a little too long on it during a busy week, and hit burnout - and thought if I front up, get another opinion then I may well get motivated to fix the damn thing 

Will remove the IC's, and probe out all the data lines. I have triple checked the jumpers, but will hit them with a "Fresh Head" in an evening or two. Fear not, this bugger is gonna run

Cheers
Jacob

I've "been there" many times, Jacob - and this is where "patience" is the key. If you can fix this board, you can fix anything. The more time you invest in it, the closer you get to the satisfying moment of the "quick flash" and those all import 6 Flashes .. ..

[ddstoys]

Keep it up Jacob you will get there 

[AskJacob]

Just have not had any smart time this week unfortunately - and don't want to try when tired/sleepy!

Just you wait till the weekend, MPU - you will obey!

Cheers
Jacob

[dj10555]

Good luck Jacob, you will get it in the end.

Would check the rom jumpers as Nino suggested. Have you tried the board with only U6, U9, U11 installed? Have you also tried the -35 chips in the M-100 to confirm these are alright? Would also buzz the following out (from www.pinrepair.com) if you haven't already, as some of the tracks between U6 and U11 passthrough U7.

I had a similar board, I repaired. It wasn't quite as bad as yours but someone had tried to remove the corrosion, lifted most of the tracks under U8 and then drilled out the hole to each pin to a larger size.


U8 pin 1 (A3) - U7 pin 20, U6 pin 5
U8 pin 2 (A2) - U7 pin 21, U6 pin 6
U8 pin 3 (A1) - U7 pin 22, U6 pin 7, U11 pin 35
U8 pin 4 (A0) - U7 pin 23, U6 pin 8, U11 pin 36
U8 pin 5 (A5) - U7 pin 18, U6 pin 3
U8 pin 6 (A6) - U7 pin 17, U6 pin 2
U8 pin 7 (A7) - U7 pin 15, U6 pin 1, U11 pin 24
U8 pin 8 - Ground
U8 pin 9   (D10)*- U7 pin 6, U6 pin 14, U11 pin 29
U8 pin 10 (D00)*- U7 pin 6, U6 pin 14, U11 pin 29
U8 pin 11 (D11)@- U7 pin 7, U6 pin 15, U11 pin 28
(* U8 pins 9&10 shorted together)
(@ U8 pins 11&12 shorted together)
 
U8 pin 12 (D01)@- U7 pin 7, U6 pin 15, U11 pin 28
U8 pin 13 (D12)*- U7 pin 8, U6 pin 16, U11 pin 27
U8 pin 14 (D02)*- U7 pin 8, U6 pin 16, U11 pin 27
U8 pin 15 (D13)#- U7 pin 9, U6 pin 17, U11 pin 26
U8 pin 16 (D03)#- U7 pin 9, U6 pin 17, U11 pin 26
U8 pin 17 (CE2) - Q5 rt upper leg, U9 pin 40, U11 pin 34
U8 pin 18 (OD) - U18 pin 6
U8 pin 19 (CE1) - U17 pin 8
U8 pin 20 (R/W) - U7 pin 16, U11 pin 21, U9 pin 34, U18 pin 7
U8 pin 21 (A4) - U7 pin 19, U6 pin 4, U11 pin 22
U8 pin 22 (Vcc) - C13 left leg, R12 upper leg, CR5 lower leg
(@ U8 pins 11&12 shorted together)
(* U8 pins 13&14 shorted together)
(# U8 pins 15&16 shorted together)
 

[AskJacob]

Top notch! Thanks for the buzz list - I was going to sit down and draw one up - now I don't need to!

Wow I bet drilling out whatever plating may have been left in the holes would have really helped that poor old MPU! Funny things people try to do to fix these!

Cheers
Jacob

[shansta]

Ha - your a brave man Jacob!

Funny things people do? I would have used that board as a frisbee! 

[AskJacob]

dammit

found some missing traces. repaired them.

then did not double check the hookup, and hooked up 12v to the 5v test point

reckon I have stuffed every IC onboard, and also blew up my logic probe.

Stuff this thing, I'm leaving it alone for a while 

[ddstoys]

dammit

found some missing traces. repaired them.

then did not double check the hookup, and hooked up 12v to the 5v test point

reckon I have stuffed every IC onboard, and also blew up my logic probe.

Stuff this thing, I'm leaving it alone for a while 

You poor bastard ive done that myself but didint kill my logic probe at the same time...   Just walk away for a while And good luck

[dj10555]

Feel for you Jacob after all the work you put in.
I have repaired boards where a higher voltage was shorted across them and have only had a couple of chips fail. Last one one repaired for someone had a 6821 and Eprom fail. Eprom would no longer read blank after erasing.

Hopefully it will be the socketed chips.

[Strangeways]

OUCH !

Sorry to hear that Jacob. Put it aside for the moment and don't worry too much about it.

[AskJacob]

Yah thanks guys. I know I am not the 1st to do it, and sadly pretty sure I won't be the last. Let's just say don't check and double check after a day's tiling :(

Obviously was too tired to do it right - so was asking for trouble...

I'll get back onto it soon (when the swearing stops) - I still have a worker so I can find which chips (if any) survived, and pick up and get back into it. Also think I will knock up a little test harness with over-voltage protection, to avoid a repeat ever happening. You think anyone else would want one while I am at it?

On a positive note, my IJ is finally all back together, and is in as good condition as it will ever be until I get round to re-decaling it (had some outstanding issues, including the optical flipper switches hacked out with SS style tungsten switches  , Jumpers set to europe, PoA out of kilter, service button dead... and so on ) - anyway, all sorted now.

Was great to have the machine on full song - 3rd game in and got grand champion (after updating the ROMs the memory had been cleared) - and even better, my wife got to come and enjoy some games on her favourite machine, at last, about 6 years after it was purchased (long story :) ).

Soooo, on that note - that is what it is about :) I got to see the end result of it all!

Thanks for the help so far (a HUGE part of this great hobby), thanks for the support, and thanks for the commiserations. I'll dust myself off and get this bloody MPU working - it was never a "commercially viable" option to repair - but now it's PERSONAL :)

Cheers
Jacob