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Tales from Midibob's workshop Proconn


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I'm working on a Proconn Plus at present which came in as a no boot. First thing to note was it had a master oscillator daughter board fitted, which I've covered in a previous article.
On intial inspection all looked good, no signs of corrosion on the board which is always a good start. On switch on it did absolutely nothing, no address or data, in fact the CPU appeared dead. Reset was fine but there was no clock!
Checking on the daughter board showed there was no power getting to the chips and after a bit of continuity checking there were a few tracks that didn't connect. Scraping off the solder mask explained why, all the copper had been eaten away!!

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This pic was taken after the repair to the board. Considering how good the main board is I suspect this daughter board has come from a different machine.

Anyway, once repaired things started to happen but only to the point of getting an alarm and a P 60 error on the display? I'm running it with Reflex software but there's no game manual for this and of course no error codes.:headache:The nearest guess is a P600 which is a meter error on a different game. Further to this R18 (330R just to the right of the yellow wired meter connector) had been suffering from heat so a new one was put in. This is part of the meter circuit and the new resistor does run quite warm, warmer than I'd expect. Everything else in the circuit apears to test OK so I'm not sure as yet what the problem is?

If somebody could confirm that it is a meter error at least I won't be chasing my tail looking for the wrong thing.

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  • 5 weeks later...

Had a couple of old type Procon boards in with fried PCB's. One with a burnt out audio chip and another with a burnt out 53v track (the worst)!

Both boards have had all the carbon dug out and replaced with epoxy with glass fibre strands added for strength. The audio chip one needed new rivets put in on a couple of pins and the track remade where the carbonated board had been removed.

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The 53v track I'm doing for my own benefit as I reckon the silicon count is going to be horrendous going by Andrew's experience. Just for my own curiosity I want to see how bad it can be so next time I can say no.:lol:

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I'll post some more pics tomorrow of the board repair and maybe some results of testing.

The other thing with these older style boards is they don't have ROM on board and need a cart.
I couldn't find any info on the Mecca so here's the board. It's very simple as there's only the single ROM chip.

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I'll see if I can make one of these single sided for a test spare. One other thing that confused me concerning the diagram for this board was I couldn't understand whay the CPU clock didn't connect to the CPU? After tracing it out on the board I came to the conclusion that there must be a wire link on the ROM cart to conect them together which indeed there was. I'll probably upload the diagram for the cart tomorrow.:)

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Actually I didn't think of doing it on that type of board. As it's so simple it's probably worth doing it that way rather than etching and drilling my own board. I've got lots to play with too. Thanks Andrew. 

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46 minutes ago, midibob said:

Actually I didn't think of doing it on that type of board. As it's so simple it's probably worth doing it that way rather than etching and drilling my own board. I've got lots to play with too. Thanks Andrew. 

tony (amot) prob has a few of the rom card you need for testing

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3 minutes ago, Andrew96_ said:

well you seem to be the only person since 2013 that's needed one so not worth getting them remade on proper pcb's as no demand! 🤣

Yep, there's not much call for these repair wise but at least I'll be ready for the next one.

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That didn't take too long, and it works too! :lol: Thanks again for the inspiration Andrew.

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The board with the burnt audio chip is now working fine. Luckily no collateral damage was caused. The 53v rail had b een patched out with a wire by the battery area and some stray voltage was still being picked up. I decided to isolate that part of the track to save any future possible burn ups in that area. Once isolated there was no stray voltage at all. However, putting the meter on the isolated track it was still showing 3-4 volts under bone dry conditions. No doubt in damper conditions it would probably track over!

The other board with the 53v rail track burnout is not quite so straightforward. It does initialise and starts with the bleeps the first time so I'm happy the CPU is running OK and it must be reading the ROM to know how to set the audio going. Other than that it goes no further. I think this will be a lockdown job!

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Well let's put it this way. The bit of track that runs along the top of the board and skirts round the battery connection is picking up stray voltage. I've cleaned the top of the board with IPA then a stronger PCB cleaner which made it better but didn't cure it.

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From that I think I would conclude that this board is contaminated within. Once I'd isolated that section, roughly between the arrows the stray voltage was gone although the isolated bit still had volts on it! I suspect that's what you found Andrew?

By the way Andrew any chance of you changing your profile photo, it makes me start itching every time I see it.:lol:

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A fair bit of time has been spent on the board with the 53v rail burn out and as expected the silicon count is horrendous.

At present all the PIO's have been swapped out, most the transistors and a few other small chips. The good news is it's now functioning, not correctly yet but at least it does run.

One issue I came across which may be of some interest was the lamp OVER CURRENT circuit. Both transistors had gone to silicon heaven and looking at the circuit all looks correct. However the board had R42 & 43 reversed so the 10K was across T14. These resistors looked original too so must have been incorrect from the factory. Comparing with the other board, with the audio chip burn out, and the resistors had been renewed and refitted to the correct way round so somebody knew this already! I've looked at some later PCplus boards and they are also correct.

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Not a particularly good pic but the 10K is R42 and the 1K R43 as per the diagram but they are the wrong way round!

Still a few issues to sort out on this board, most things are working although something isn't right on the lamps somewhere. I can get it to clock up credits but it won't play correctly and this is only with the door open. With it closed it just alarms so there's still a little gremlin in there somewhere.:headache:

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Amazing work Bob!  How you've managed to get both of the boards working is astonishing, thought maybe 1 (at a push) as they were pretty badly burnt up.

Absolutely belliant Bob

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  • 2 weeks later...

Cause for a cold beer this evening as I managed to get the PC Plus working that had the P 60 come up on the 7 Seg display but didn't do anything else. Looking at the post it was the 1st October!! Folks in the know suggested it was probably a PIO gone down and the only way to find it was to swap them out one by one:headache:I'd been putting that off for as long as possible as it takes a good day to get them all done.

Scope checks didn't really reveal anything except a couple of output lines from the CPU were slightly lower than other boards. I thought I'd start replacements from right to left so in with a new CPU and no difference. CTC was next and again no difference. I thought I might as well do the RAM as it's only 24 pins not suspecting it for a minute. Nope, still the same.

Moving left the 1st PIO was swapped and again no difference. You're probably getting way ahead of me here but the saga contined till we got to PIO 5 but again still no difference! All that was left was the SIO and if it wasn't that I was going to jump in the Thames.

So in goes a new SIO and bingo she boots!!!! Yeehaw. Now why couldn't I have started left to right.:clown: Back tracking and replacing all the original chips showed they were all blameless. Preliminary tests looked good with game play working but no meters. This was due to the meter driver chip (ULN2803). Hopefully I can wrap this one up tomorrow as it's well overdue.

I've had some real horrors recently and I've still got two MMM's giving me grief. I will beat them eventually.:D

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