Dear diyAudio Community,
I'm currently restoring my Technics SU 8080 integrated amp. I replaced all the electrolitycs, except the power supply ones, with Panasonc FCs, FRs and Elna Silmic2s. Cleaned allthe switches, pots and the speaker relay. Replaced half of the small transistors and all double transistors (2SA798). I know this issue had been somewhat discussed on Audiokarma forums before and no one really had an answer. I'm hoping, that since then, maybe, someone on this forum managed to actually get this power limiter boards adjusted according to the service manual or not.
I used the service manual for all the adjustments as follows:
1. Adjustment of (-B) voltage (negative power supply). I adjusted it to -44.5v according to the service manual with no problem;
2. Adjustment of speaker terminal DC balance. I adjusted it according to the service manual to 0mV, both in "DC" and "low cut" switch positions with no problem;
3. ICQ (idling of power transistor) adjustment. I adjusted it according to the service manual to 15mV with no problem;
4. Adjustment of power limiter is THE PROBLEM for me. I could NOT adjust these boards’ value according to the service manual at all. Whatever I do with trimmer potentiomenters R350 and R351 according to the service manual the waveform on the oscilloscope screen does NOT change all, niether its' vertical symmetry, nor its' amplitude.
So, has anyone actually managed to adjust this power limiter boards on the amp as per service manual or adjustment section Number 4?
What 1kHz test signal amplitude/voltage has to be applied to the amp input?
Do you need to connect resistive load (8 or 4 Ohms) to speaker terminals for this adjustment to be made? The service manual doesn’t tell anything about test signal amplitude/voltage or resistive load for this adjustment.
Sincerely,
Ivan Terekhov
I'm currently restoring my Technics SU 8080 integrated amp. I replaced all the electrolitycs, except the power supply ones, with Panasonc FCs, FRs and Elna Silmic2s. Cleaned allthe switches, pots and the speaker relay. Replaced half of the small transistors and all double transistors (2SA798). I know this issue had been somewhat discussed on Audiokarma forums before and no one really had an answer. I'm hoping, that since then, maybe, someone on this forum managed to actually get this power limiter boards adjusted according to the service manual or not.
I used the service manual for all the adjustments as follows:
1. Adjustment of (-B) voltage (negative power supply). I adjusted it to -44.5v according to the service manual with no problem;
2. Adjustment of speaker terminal DC balance. I adjusted it according to the service manual to 0mV, both in "DC" and "low cut" switch positions with no problem;
3. ICQ (idling of power transistor) adjustment. I adjusted it according to the service manual to 15mV with no problem;
4. Adjustment of power limiter is THE PROBLEM for me. I could NOT adjust these boards’ value according to the service manual at all. Whatever I do with trimmer potentiomenters R350 and R351 according to the service manual the waveform on the oscilloscope screen does NOT change all, niether its' vertical symmetry, nor its' amplitude.
So, has anyone actually managed to adjust this power limiter boards on the amp as per service manual or adjustment section Number 4?
What 1kHz test signal amplitude/voltage has to be applied to the amp input?
Do you need to connect resistive load (8 or 4 Ohms) to speaker terminals for this adjustment to be made? The service manual doesn’t tell anything about test signal amplitude/voltage or resistive load for this adjustment.
Sincerely,
Ivan Terekhov