Tea-Bag

Replaced Q4 - still same appoxiamate voltage .765Measured again Q6 - - ~ -12v like last time.Good channel Q4 - ~2V, Q6 around - 6V (I think). Not as high. No BF245's around to swap out.Thanks for looking.

Yes, those are fine on both channels.

250R, 310R, did not work. I remember after replacing Q14, but not fixing short around R27, that it biased up to .750, but after fixing it, I got this. I had de-soldered most of the upper right part of the schematic trying to figure that out, maybe something toasted there, but uncertain. Drilling that area, really just takes the R27 to C3 track out of the picture.Everything around 'front end Jfet's' look good.

No worries. Q13 - 1.31 UgS @ 2A, Q14 1.42 UgS @ 2A

Of course I am the murderer. It's been awhile sense I've been in a good mess. For now I will leave the crime scene alone.

No worries about time at all. Hope you get well and have fun with friends.Zeners are on order - grounding of input's yes. Figured I would ask some questions before replacing more stuff.Generg, lots of other projects to work on.....House stuff, garden stuff, and building some MJK baffles to listen to various 3-4" full rangers I have around.

Hi Guys, Hooked up the bad channel to the fet's - hasn't gone to well. It's getting embarrasing. This board has had a hard life with me as a father. I am getting a bunch of odd voltages, thought it was the optocoupler, but replaced that to no effect. I've taken the voltages, and added them to the attachement. I've tested the R100's solo and they test fine, and kept Vgs values as before, but in circuit - no love. Q13 in this case seems like it's getting nothing to work with. Most interesting is the 3v6 reading - to be taken from pin 5 on CNY17 to Drain on Q 14, shows 0v here. My intuition tells me to replace Q4 and Q6. The voltage across R35 should be at least double....The voltages are certainly not right there. My understanding of the working's of the circuit are not deep enough to understand where this is going wrong. Any help would be appreciated. edit : schm deleted by ZM

So this shows the mod I made to stop the short from happening. Other channel was fine. Sorry for the bad modified pic.The track looks plenty far away, so not sure what happened.Anyways, Q8 gets full voltage over it now, and things are looking good. The 2SJ's are still getting only 10.5v, should I add another LED on to add some voltage? Will it make a huge difference sonically? Maybe I should find out myself.Current over 4.7r's is 23.5mv and R9 is 9.4v.Next step is to add the R100's back in and see if I can get the offset reasonable. :crazyrocker: I can't decide what to start on for gate resistors. I have 33R. 47R and 180R's, no 100R's like Generg used.

I solved the short by drilling out the connection at C3 and one at R27. So some contact was made by the close track there it appears.Of course, I disassembled that section of the board to see if some component was doing this. I replaced the LED with 20MA last week. So I will re-assemble the other parts on there, and report back. The board is made nice, no track has lifted with my de-soldering.

Okay,Outputs removed, input shorted, output shorted. DC to 15.5v Changed R35 to 180R, reads 1.8v Changed R23 to 47R, still reads 0V R3 to 9.4v R12 and R25 to 0R 4.7R's all read 23.5mv, all 2SJ74's show 10.4v R26 is 2.0v Replaced opto-coupler as well, and Q7. Thanks a bunch, and rest well. I am no rush here. One oddity I have noticed is that with R27 installed (33R), the gate to Drain shorts, with R100 installed or not. I don't forsee it causing this issue, but, I cannot repeat this on the working channel.

Yes, before to measure vgs. In circuit vgs, they appear to be quite close to original measurements, of course now the pair on installed is not too well matched.Q13 ~1.3v Q14 ~1.4v vgs measured in circuit at startup. This is of course without Q8 apparently conducting.I will do as you say and remove them from PCB, re-test, and test PCB without R100 Jfets.

Yes it is! I am still using test speaker, but sound is promising.

More or less went by this process, had to get voltage across R3 up, and fiddle with R12 for Source voltage up as high as I wanted to go to in test phase with Channel 1.Channel 2 more or less never behaved or has responded to R12,R25 Pot.I will take the Fet's off bad channel and do measurements as you ask.

no luck replacing Q8 again.

Maybe I should replace Q8 again after Q14 blew.

Yes, I have a variac. But I test up to full voltage for reference. Offset on left pic is ~10mv. I found the biggest influence of this was R9, then R12,R25.Meddling with the pots on the right pic, has no influence, stays about 20v.Not sure what's broke here, although 2SJ74 pairs are a little off, and now R100's a little off Ugs. But I think the problem with Q8 has me most worried.

I made some progress last night. I measured everything at voltage, good and bad. For better or worse, Q14 on bad channel sputtered and blew out white smoke like a steam engine and blew fuse. Repalced it with a mismatched vgs one, and offset is bad, Q8 still no voltage (I checkd CNY17, both channels are the same). Q14 still runs hot at start as well, so worried it might blow. I measured voltages and continuity in the R23,27, 26 area, all looks good. I am using 60.4R on R23. Maybe my bad or from old schematic. Anyway's hope these look good.edit : schm deleted by ZM

No hurry.I replaced Q3, Q8, still same results for them, 0v.Hmmm, must be something else Will measure some cold resistance values and continuity on both unit's see if something's amiss there, although it feals like a transistor failure somewhere.

After much hassle fro Generg, I replaced LED in both BJ2 boards.Still one board biases too high.I measured around against working channel to look for differences. Here they are. I didn't compare everything.Q3 - OV on bad unit 9V on good unit.Q8 - 0.3V on bad, ~19v on good unit. Both measured on From Collector to Emitter. I am inclined to think one of them is toasted.Too tired to replace them to see if that works. I need to dig around for more PNPs.I think the solder connections across R23,24 are all good. Q3 doesn't seem to be too close here, so not sure why both measure 0v.Lazy American looking for ideas

thanks, I will get an order in today.

In any case, I need to replace them. Can't be working right.I will use these, They take more current and are 1.9v ref.http://www.mouser.com/Search/ProductDetail.aspx?R=HLMP-S201virtualkey63050000virtualkey630-HLMP-S201Yes, they flickered with the music...Somehow. Surely a warning things were not good.

Oops. I ordered http://search.digike...rds=516-1310-ND for my LED's. Think they are 2mA typical. This might explain why they are flickering a bit with a signal pumping into it? Congrats Generg, I am a further bit behind. Have a nasty cold. I have one channel with minimal offset, .750v across source resistors, the other is offset of 10v, and it biases to 1.8v quickly. Something wrong with it, it didn't respond to R12 or R25 fiddling at all. Maybe swapping out LEDs will get me further down the road.. I do need to take some serious measurements of both channels and present them here. Generg, Once you go full range driver, I think you'll be happy. What implementation for Sonidos you going to use, BLH, OB? Tea-Bag

I found two big round one's.

We will see..I would run on Lowther PM5A on top of lowther open baffle. My listening area is part of main living area, 5m x 12m.What is 'donut' size? I will take a look around for a choke. Else, have somebody wind one.

I hope to. I don't know if I will spring the cash for a 'big choke', but will look into building the CCS'd version. Esp if it's got a free eagle file. :Viannen_loungelizard:I don't know if my metal work will look like a Magura UFO, but maybe something that runs on plywood. Maybe even 'hardwood' plywood.Otherwise, look forward to more details, and if it sounds better or worse than BJ2.