All values are DCV
R3: -0.079
R4: -0.007
R5: 0.002
R6: 0.0
R7: 0.0
R8: 0.0
R17: -0.003
R18: -0.219
I don't think this patient has a pulse. The first time I turned the F5 on with the new mono PSUs and the amp boards attached I got music out of both channels but the sound was poor. So I rebiased the right channel but had no luck biasing the left channel which is its current state. The amp boards were previously biased for the basic F5 build I decided to move to the dual mono build. I don't think in my various testing since then that I caused a voltage shock to the left channel, unless I did it that first time.
Looking at your numbers:
- voltage too low at R4 - bad 2SJ74, replace.
- voltage too low at R17 - bad ZTX550, replace.
-voltage at R18 low - may also be bad, so replace ZTX450.
Once that is done, be sure that the trimmer pots are at their initial powerup position, power up with a DBT, and check if the bias adjustment works and the mosfets turn on.
The channel was likely damaged when you first powered up with the new power supplies. The sound would not have been poor if everything was working properly at that time.
- voltage too low at R4 - bad 2SJ74, replace.
- voltage too low at R17 - bad ZTX550, replace.
-voltage at R18 low - may also be bad, so replace ZTX450.
Once that is done, be sure that the trimmer pots are at their initial powerup position, power up with a DBT, and check if the bias adjustment works and the mosfets turn on.
The channel was likely damaged when you first powered up with the new power supplies. The sound would not have been poor if everything was working properly at that time.
Ben,
Thanks for the analysis. I will get right to rectifying this.
Lessons learned, use a DBT even when you don't think you need to.
And when I port my F6 over to dual mono, reset the pots to bias both amp boards once PSU's are stable.
I see the ZTX 450/550 are sold out worldwide. I can try ordering from eBay, but if anyone has two spare units, I would appreciate it and happy to trade parts or cover the costs.
Thanks for the analysis. I will get right to rectifying this.
Lessons learned, use a DBT even when you don't think you need to.
And when I port my F6 over to dual mono, reset the pots to bias both amp boards once PSU's are stable.
I see the ZTX 450/550 are sold out worldwide. I can try ordering from eBay, but if anyone has two spare units, I would appreciate it and happy to trade parts or cover the costs.
This is why I'm not a brain surgeon....
No wonder the 2SJ74 wasn't working....one of the three legs was broken. Too much rough handling on my part. I tested it and it still works.
What if I just swap that out for a new one before I make the other swaps? I'm confident I caused that breakage before I first turned on the PSU for that amp board. Would that broken JFET make it unlikely that any other parts got damaged?
No wonder the 2SJ74 wasn't working....one of the three legs was broken. Too much rough handling on my part. I tested it and it still works.
What if I just swap that out for a new one before I make the other swaps? I'm confident I caused that breakage before I first turned on the PSU for that amp board. Would that broken JFET make it unlikely that any other parts got damaged?
If you were able to test 2SJ74, perhaps you can solder a lead on the broken leg and re-install it on the board.
The ZTX550 is on the opposite side of the circuit (2SK170 side) so I don't think it was affected by the 2SJ74. It most likely still needs replacement.
So if you can repair the 2SJ74, re-install it and power up and see if it works, and re-measure the voltages.
The ZTX550 is on the opposite side of the circuit (2SK170 side) so I don't think it was affected by the 2SJ74. It most likely still needs replacement.
So if you can repair the 2SJ74, re-install it and power up and see if it works, and re-measure the voltages.
Tested (cause we don’t need another issue) and dropped them in the mail this morning.
Update on my Duo-Mono Conversion of my F5.
With lots of help, I'm listening to it right now. Sounds punchier, but that could just be my biased listening. Time will tell. No, I think it is driving my Magnepan 1.7i's deeper now.
This was a great build project. Thanks again to DamonB over in the F6 thread who showed me the way.
And thanks to everyone with the help and support.
With lots of help, I'm listening to it right now. Sounds punchier, but that could just be my biased listening. Time will tell. No, I think it is driving my Magnepan 1.7i's deeper now.
This was a great build project. Thanks again to DamonB over in the F6 thread who showed me the way.
And thanks to everyone with the help and support.
Attachments
I'm building new F5 boards and I'm having a heck of a time finding the NTC 4.7K thermistors. All I come up with are SMD parts. I've searched this thread and the only reference is this posting. What am I missing?
Thanks
https://www.mouser.com/c/passive-components/thermistors-ntc/?resistance=4.7 kOhms
That will get you started.
That will get you started.