slimecity
Super Member
Kev you were very lucky - for sure.....I am still having issues. Although Im prepared to be VERY patient as this is a special amplifier.....
So I have sacrificial outputs mounted in the bias monitoring sockets on both sides - FYI.
I fired it up again and started taking measurements. The good news is that now I am getting stable bias on both modules.
The bad news is the crazy jumping around DC offset on both sides - from 0 up to 4 or 5 volts. Once side is slightly more erratic than the other.
I also disconnected the grey wire leads 12 and 13 to the triac - however this had no effect. Seems I have the same issue which is independant and on both sides.
I then got annoyed that the DBT was preventing me getting more accurate readings, so I bypassed it - it wasnt glowing bright anyway. After that I got exactly 100VAC being fed into the amp.
Before I look into this DC offset issue further however - I revisited the power supplies to the power modules and one of these supplies is not right. My understanding is that there are TWO DC powersupplies going to each module:
- The first one is the supply from the large capacitors - this is fine - around 65-66VDC (from each rail in relation to ground), but
- The other supply - going to pins 6,7,8 on both modules are both down - Im getting 50VDC on each one (from each rail in relation to ground). I take it this supply is also supposed to be 68V?
The other thing is that I took measurements on TR01 on the main powersupply/protect board F2781 - instead of having 23V on the emitter of TR01, I am getting 14V. All other readings (for R601 and TR602 are fine).
Any suggestions on where to look first for the reduced powersupply voltages - if these are indeed down.....this isnt great - Im a bit worried I have a damaged trafo - I will test those secondaries and the bridges tomorrow.....
So I have sacrificial outputs mounted in the bias monitoring sockets on both sides - FYI.
I fired it up again and started taking measurements. The good news is that now I am getting stable bias on both modules.
The bad news is the crazy jumping around DC offset on both sides - from 0 up to 4 or 5 volts. Once side is slightly more erratic than the other.
I also disconnected the grey wire leads 12 and 13 to the triac - however this had no effect. Seems I have the same issue which is independant and on both sides.
I then got annoyed that the DBT was preventing me getting more accurate readings, so I bypassed it - it wasnt glowing bright anyway. After that I got exactly 100VAC being fed into the amp.
Before I look into this DC offset issue further however - I revisited the power supplies to the power modules and one of these supplies is not right. My understanding is that there are TWO DC powersupplies going to each module:
- The first one is the supply from the large capacitors - this is fine - around 65-66VDC (from each rail in relation to ground), but
- The other supply - going to pins 6,7,8 on both modules are both down - Im getting 50VDC on each one (from each rail in relation to ground). I take it this supply is also supposed to be 68V?
The other thing is that I took measurements on TR01 on the main powersupply/protect board F2781 - instead of having 23V on the emitter of TR01, I am getting 14V. All other readings (for R601 and TR602 are fine).
Any suggestions on where to look first for the reduced powersupply voltages - if these are indeed down.....this isnt great - Im a bit worried I have a damaged trafo - I will test those secondaries and the bridges tomorrow.....
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