Yes, if the problem lies in a pair, the fix should have IDSS matched units.
This RDS method is a fast painless indicative method. Not exact or fully conclusive but practical. In any case also compare the Ohm readings of the high offset pair units to the units of the low offset pair.
Hi Salas,
one of them reads 98ohms while the rest tests around 30ohms. Is a high resistance indication of short? If so do I need to replace them in pairs? I assume the pairs are next to each other.
one of them reads 98ohms while the rest tests around 30ohms. Is a high resistance indication of short? If so do I need to replace them in pairs? I assume the pairs are next to each other.
Its not a short indication but maybe of another anomaly. The pairs are JFETS 1&2 3&4 in the quad. Is it located in the pair of the high offset channel?
I just replaced the jfets 1&2 . I assume they are related to the high offset channel but the readings are still the same on the offset -16.3mV on the left and 9.80 V on the right offset.
Replaced all the 4 jfets and the DC offset are still way off @ 9.56 VOLTS(!) for the right and 21.8 mV on the left. Something is still off.Could the relay have anything to do to this? Or the C550? C517?
The relay is passive and the BC transistors are its coil drivers not belonging to the audio circuit. What relay type number you used? Are those JFETs measured for IDSS and matched by you? Where did you get them? Can I see a close up photo of one? Clean the board's solder side thoroughly with alcohol also.
When the supplies give right rails only the JFETs signal quad remains to fault. Either to be faulty or grossly mismatched. IDSS is inversely proportional to RDS. Cross check your IDSS matching vs Ohm measurement between D & S. Matched JFETs should not measure different for RDS Ohm.
BTW the relays are 12v Panasonic from Mouser, the Jfets I don't remember now where I got them. This project started in 2018 and I only continued working on it last year.