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Centaur Squawk & Talk Help

Ruk

Ruk

Registered
Joined
Sep 19, 2016
Messages
87
Location
Manchester UK
So, after what feels like a bloomin' age of remedial work on this S&T board... I've finally got a 4th flash, a huge step for me but something's not right.

I have a booting MPU (7 flashes) every time and at the same time time the S&T initiates. Up until today I could only ever get 3 flashes (out of 4) after every stage of working on the board.

The issue is probably best illustrated in the video but basically... boot from having been off and I get the 4th flash but it is very slow to do so. Switch machine off and rapidly back on (25 seconds on the vid) and the 4th flash is there a lot sooner accompanied sometimes by a single sound then no more sounds at all. The machine itself continues to go through it's boot sequence. Even switching off for a couple of seconds a switching on again delays the 4th flash long enough to not get that one game sound at all. Also, the longer I leave the machine in attract mode prior to rebooting, the quicker that 4th flash displays.

Just for some background... here is what's what and what I've done so far recently.

Say It Again board disconnected and FF linked to compensate.
All board links checked (and checked over and over) to ensure correct config for Centaur roms.
No 'AY-8912' chip installed - so all EE links in place.
Every chip socket that is utilised replaced with turned pin sockets.
Checked all resoldered joints flow to pcb pad on reverse side completely.
All existing solder on pcb reflowed.
All pcb tracks checked for continuity and/or breaks throughout.
Pin headers removed and cleaned, board solder removed and fresh solder applied.
New MC6802P fitted (in place of 6808), Ram chip removed and link 'K' made and link 'L' removed.
New PIA chips fitted.
New 4049 buffer/inverter fitted.
New electrolytic caps fitted throughout.
New 1k trimmer pots fitted.
TMS5200 carefully removed - legs not too bad just tarnished so cleaned and refitted.

These are the voltages at test points - all the TP1:

TP2 - +5.16v
TP3 - +13.9v (too high?)
TP4 - -5.0v
TP5 - varies with pot postion read at +3.94v and +2.8v
TP6 - varies with pot postion read at +3.53v and +2.4v
TP7 - +1.5mv
TP8 - +2.56v
TP9 - 0v
TP10 - +3.3v
TP11 - 0v
TP12 - +4.82v


Anyway, I'm at a loss at the moment, could this be a timing issue? capacitor charging? I dunno... I've really felt I've got somewhere to even get this 4th flash... but feel like banging my head against the wall at the same time.... HELP! haha :)

Thanks for at least reading this far and sorry for the poor phone video :)

 
Well I think I'm goosed and almost ready to hold up the white flag now, I've come about as far as I can. I would have loved to have had a spare and rare TMS5200 chip (or even a 5220) to eliminate any issues with mine which could be the final hurdle with this problem, I'm just dancing in the dark with it :hmm:

The above description and video where I was getting an intermittent delayed 4th flash is now totally non existent and I am back to only 3 flashes every time I switch on. I found a very high resistance solder pad on one of the PIA chips and duly sorted it... from that point to this only 3 flashes.

I wanted to try and rectify this problem before I do a full cabinet strip down and a playfield rebuild... not to be. Ah well, at least I've tried and give it a right good old go... I can always drop back onto it again at some point :cuckoo:
 
Good advice from @stoptap you need a "decent" True RMS mutlimeter to test this (note Fluke used in link) - a good way to check is to measure a known DC source (such as a 9V PP3 battery) with setting at AC, if you see +18V (which cheap ones will) you need a better meter.
 
Ruk said:
Well I think I'm goosed and almost ready to hold up the white flag now, I've come about as far as I can. I would have loved to have had a spare and rare TMS5200 chip (or even a 5220) to eliminate any issues with mine which could be the final hurdle with this problem, I'm just dancing in the dark with it :hmm:

The above description and video where I was getting an intermittent delayed 4th flash is now totally non existent and I am back to only 3 flashes every time I switch on. I found a very high resistance solder pad on one of the PIA chips and duly sorted it... from that point to this only 3 flashes.

I wanted to try and rectify this problem before I do a full cabinet strip down and a playfield rebuild... not to be. Ah well, at least I've tried and give it a right good old go... I can always drop back onto it again at some point :cuckoo:
Click to expand...

Go back to the solder pad and redo you fix or undo it and see if you get the 4th flash back, that's obviously the problem area if you're down to 3 flashes.
 
astyy said:
Good advice from @stoptap you need a "decent" True RMS mutlimeter to test this (note Fluke used in link) - a good way to check is to measure a known DC source (such as a 9V PP3 battery) with setting at AC, if you see +18V (which cheap ones will) you need a better meter.
Click to expand...

Thanks for that... it's all good advice. I'll follow that procedure and see how it goes. :thumbs:
 
Moonraker said:
Go back to the solder pad and redo you fix or undo it and see if you get the 4th flash back, that's obviously the problem area if you're down to 3 flashes.
Click to expand...

Although this sounds quite logical, and it did to me, the pad/leg in question on U7 wasn't making contact at all as it should be and the 4th flash was so intermittent, I think my rapid switching the machine off and back on again was just 'tricking' the self test somehow. Removing the IC pin to circuit is something I could look into when I get back onto the testing... You are right though in thinking that it is in this area, as is the adjacent TMS5200 chip.
 
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