Ok - so my Defender with it's current MPU board seems to be working fine at the moment, although it was recently throwing RAM errors I was told. It's been in foster care for some time (a few years), so figured I'd give it all a once over to be sure it's in good shape, and also go through some extra MPU boards I've got laying around.
Board that's in there seems fine - but in checking my voltages, my 12v is around 11.6v (from the PSU board, with no load), and around 11.5v on a 4116.
5v is around 4.8v on the PSU, and 4.3 to 4.5 (depending upon the MPU board used) at the RAM. Stays close to 4.8v on the ROM board otherwise.
-5 is rock solid, at both the PSU and the RAM.
Both of the extra boards have issues - one won't reset until I manually ground pin 37 of the CPU, at which point it boots, but blind - no video. Second board is just watchdogging constantly. In both cases, I suspect the low 5v is a factor, and it doesn't make much sense to start digging deeper until I'm confident my voltages are closer to spec.
PSU was re-capped a couple of years back, and game has had light use since. All headers are good - they were replaced, and still look great - no burnt pins, no cracked joints. BR2 was also replaced at the time. I've recapped the MPU boards as well.
So - seems like something's pulling the 12v and 5v down on the PSU board slightly. BR1 looks good (solder joints good, no obvious issues). Should I suspect the two 723's? Would the 18k and 4700 cap's factor into this, since those weren't swapped?
I *think* the 2N6057 was swapped, but it's been a while and I'm not positive. I've got 26.2v at pin 11 of the 723 @ IC1 - a bit lower than the 27.4 listed on the schematic, so perhaps it's BR1? TP2 has 14.2v (a bit higher than the 12.8v listed) otherwise. Pins 5 & 6 are 4.8v and 6.9v respectively on IC1 - both about .3v low compared to the schematic.
I've read about swapping out R2 for a 5k pot to allow for manually adjusting the 5v, but I'd rather get the voltages solid and where they should be if possible before considering that.
Suggestions and additional testing appreciated! I think I still have the 723's around from when I originally repaired the board, so if they're suspect, I could pretty quickly rule them out.
Board that's in there seems fine - but in checking my voltages, my 12v is around 11.6v (from the PSU board, with no load), and around 11.5v on a 4116.
5v is around 4.8v on the PSU, and 4.3 to 4.5 (depending upon the MPU board used) at the RAM. Stays close to 4.8v on the ROM board otherwise.
-5 is rock solid, at both the PSU and the RAM.
Both of the extra boards have issues - one won't reset until I manually ground pin 37 of the CPU, at which point it boots, but blind - no video. Second board is just watchdogging constantly. In both cases, I suspect the low 5v is a factor, and it doesn't make much sense to start digging deeper until I'm confident my voltages are closer to spec.
PSU was re-capped a couple of years back, and game has had light use since. All headers are good - they were replaced, and still look great - no burnt pins, no cracked joints. BR2 was also replaced at the time. I've recapped the MPU boards as well.
So - seems like something's pulling the 12v and 5v down on the PSU board slightly. BR1 looks good (solder joints good, no obvious issues). Should I suspect the two 723's? Would the 18k and 4700 cap's factor into this, since those weren't swapped?
I *think* the 2N6057 was swapped, but it's been a while and I'm not positive. I've got 26.2v at pin 11 of the 723 @ IC1 - a bit lower than the 27.4 listed on the schematic, so perhaps it's BR1? TP2 has 14.2v (a bit higher than the 12.8v listed) otherwise. Pins 5 & 6 are 4.8v and 6.9v respectively on IC1 - both about .3v low compared to the schematic.
I've read about swapping out R2 for a 5k pot to allow for manually adjusting the 5v, but I'd rather get the voltages solid and where they should be if possible before considering that.
Suggestions and additional testing appreciated! I think I still have the 723's around from when I originally repaired the board, so if they're suspect, I could pretty quickly rule them out.
