ref. to schm in post #2223
still without pucks connected to circuit
remove Q1, Q2
now, to establish DC path for NFB, allowing FE to self-center, put short (piece of wire) connecting B to E pads of Q1
if parts are OK, you'll have so-so close to 0V at output and close to red written check values on FE specific places/components
if not, pull one by one actives from FE and check them - DMM diode test, Chinese MultiGizmoTester
still without pucks connected to circuit
remove Q1, Q2
now, to establish DC path for NFB, allowing FE to self-center, put short (piece of wire) connecting B to E pads of Q1
if parts are OK, you'll have so-so close to 0V at output and close to red written check values on FE specific places/components
if not, pull one by one actives from FE and check them - DMM diode test, Chinese MultiGizmoTester
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By jfets do you mean the tiny SMD pieces, or the "T" three leg devices? I will strip the whole board if necessary (except ity bity smd) I think you are just talking the smd j fets, as you already had me replace some of the "T" units (T6 and T7) already. I gotta ask!
I see close to Q1 and Q2 these pieces I wondered about. LT 30922, VR1 and ZD1.
I will remove and test zeners out of circuit, getting anomalous readings in circuit. One measure something both ways, one nothing one way, something the other direction, so perhaps one is dead? Will find out once removed and tested in tester device.
I see close to Q1 and Q2 these pieces I wondered about. LT 30922, VR1 and ZD1.
I will remove and test zeners out of circuit, getting anomalous readings in circuit. One measure something both ways, one nothing one way, something the other direction, so perhaps one is dead? Will find out once removed and tested in tester device.
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you got pcbs with 4pcs of SMD JFets - 2SK2145BL presoldered
there is a provision for TO92 JFets on pcb (say 2SK170 or 2SK363 or 2SK369) instead of smd ones, but - logically - they're not present
checking all passives and actives in situ is normal procedure, removing from pcb and testing, in case of any dilemma
LT3092 is precision CCS, protected as Koala, having current mirrors on top and bottom
pretty much not having anything with FE problems
there is a provision for TO92 JFets on pcb (say 2SK170 or 2SK363 or 2SK369) instead of smd ones, but - logically - they're not present
checking all passives and actives in situ is normal procedure, removing from pcb and testing, in case of any dilemma
LT3092 is precision CCS, protected as Koala, having current mirrors on top and bottom
pretty much not having anything with FE problems
Presoldered, yes. Gremlins probably there
And even Koalas can’t be helped even when protected: https://www.livescience.com/animals...iful-theyre-causing-problems-howd-that-happen
So far, Zenmod seems to think problem not with them, but somewhere in other actives. So I'm in process, all set up, ready to solder in place wire short on Q1. Then measure basically same front end measurement you did, IF it first passed near 0 volts at output test. If not, and I expect not, begin removing and testing transistors.
Did you have to remove zeners out of circuit to get them to test? I'm going to remove mine to test, measured odd in circuit. Also distinct possibility I have no idea what I'm doing.
First channel was easy fix. Same parts smoked on this channel, but remains unfixed. Something else obviously was damaged. Super glad I snagged this desoldering station!
Did you have to remove zeners out of circuit to get them to test? I'm going to remove mine to test, measured odd in circuit. Also distinct possibility I have no idea what I'm doing.
First channel was easy fix. Same parts smoked on this channel, but remains unfixed. Something else obviously was damaged. Super glad I snagged this desoldering station!
@Russellc this is not very timely, I purchased a Hakko desoldering gun from a Japanese vendor, took about 1 week. I have only used it to desolder 1 wire from a pcb, but wow! Yes, I know, I'm a sissy 
but I'd rather be doing that than that, if you catch my drift. It ended up costing just under $180, and if my first experience is indicative, well worth it! If you like PM and I can give you the vendors info.
but I'd rather be doing that than that, if you catch my drift. It ended up costing just under $180, and if my first experience is indicative, well worth it! If you like PM and I can give you the vendors info.
@Toys4Boys results with the 100V version of the Hakko 301 have convinced me to give it a try. I've never had issues with the big solder suckers, but I'm a big fan of having "the right tool for the job", so I grabbed one. Half the price of the US 120V version and worst case, I'll use my old variac to set the 100V input. I suspect it'll work just fine at 120V....a little more suction and higher temps than listed with the only concern "currently" (punny) being the higher voltage could reduce the lifetime of the unit.
To help bring it back on topic, I'm closely following @Russellc troubleshooting progress on the XA252. I've got this build on my short list and soon hope to be fabricating one for myself. Currently dealing with a TMP issue...(too many projects).
To help bring it back on topic, I'm closely following @Russellc troubleshooting progress on the XA252. I've got this build on my short list and soon hope to be fabricating one for myself. Currently dealing with a TMP issue...(too many projects).
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I already bought a desolder station. Works like a dream. Just put it on backside, solder melts, end of wire goes in hole, hit sucker trigger, clean as a whistle. The six legs of the double transistor sandwich of Q1 and Q2 desoldered, whole unit lifted out of holes.@Russellc this is not very timely, I purchased a Hakko desoldering gun from a Japanese vendor, took about 1 week. I have only used it to desolder 1 wire from a pcb, but wow! Yes, I know, I'm a sissy
OK I did first measurement but not sure if I am measuring correctly. You said I should have 0V at output. I "assumed" by output you mean speaker output.
So I measured 2 ways, see if one is correct.
First way was multimeter pos to + speaker out put and ground (on board). That gave me 9.3 mV.. Fearing incorrect measure method, I also measured on both speaker outputs, like if measuring for DC offset. That measurement is 9.5 mV.
This is with "slightly tanned" R24 still in place. hopefully this is correct measurement method, but since not 0V, I assume I need to start removing the actives
you spoke of needing put in tester gizmo to see if cooked.
Otherwise, what did I do wrong this time? Will fix it..