Are you taking about the 2 BBQ'd resistors - R23-24? Change those for sure. I assume those cooked when Q6 had a problem. Hopefully that's the extent of it. I hope Q7, Q9, D1, and associated resistors are good. Start with R23/24 and we'll soon see.
Check solder on Q4.
Check solder on Q4.
Just got back. Both R23/24 burned immediately on power up. D1 is lit. Solder on Q4 is OK. I'll look at the resistors on Q7 and Q9.
Do you have a transistor tester? And what solder remover tool are you using? It it easy to pop out and check Q6, Q7, Q9?
R25, 36, 27 are good. As noted D1 lights. I've got a Hakko fr300; so I can get them out. Got a mega 328. It'll probably test Q9, but it would not test Q6. I think I have an old dmm that could test transistors. I pull them out and see what happens, otherwise I'll get them all tested by Monday.
Got them both out. Oddly enough, Q7 tested - good. Q9 wouldn't test. My sense is that Q9 is OK. If so, what would be next.
What do you mean by “wouldn’t test”? What does the tester show? Should you assume it’s blown?
I have been there and done that.
It has been a few years ago I exploded a capacitor or two with tube amplifier 400VDC voltages.
Now I fire things up inside 16 gauge electrical j boxes. And or use the bench power supplies that Santa brought to my lab. The kind of power supply you can set a limited current and limited voltage. Then turn the juice up in limited increments avoiding wrong way capacitors from venting in your face.
Good Luck DT
It has been a few years ago I exploded a capacitor or two with tube amplifier 400VDC voltages.
Now I fire things up inside 16 gauge electrical j boxes. And or use the bench power supplies that Santa brought to my lab. The kind of power supply you can set a limited current and limited voltage. Then turn the juice up in limited increments avoiding wrong way capacitors from venting in your face.
Good Luck DT
I don’t know that tester specifically. But I would assume if a transistor doesn’t read as the expected type of transistor then it is blown. Sometimes I see blown transistors as 2 diodes instead of NPN, for example. Then I know it’s time to swap in a known good new one. I test the new one in the tester to be sure.
The super inexpensive (el cheapo) Mega328 component tester, which sells for about USD 12 without acrylic case on eBay, achieves its amazingly low price by making some compromises. As a result, it gives the right answer most of the time --- but not always. Many diyAudio members have discovered that, for example, Mega328 doesn't recognize a Toshiba 2SK170BL as an Nchannel JFET. But it does recognize a Fairchild J113. Oof.
120 generally. and that is with the variac set at 120, however close that is. Normally house juice is 120.
I mentioned that the Mega 328 would not test Q6, but did test the Q7 that I removed;. Nothing I have around gives me a reliable test on Q9; I've ordered a few on Amazon that will be here tomorrow.
Ironically, I have a Digilent AD2 system. They released a Transistor Tester module several months ago. I bought one, put aside, and promptly forgot about it. I found it this morning, but cannot - so far - make it work. I'm sure I'll have it figured out in a week or so (when I won't need it).
Got a hold of a reliable transistor tester. Here's the status of the circuit:
Q6 - NEW
Q7 - TESTS OK
Q9 - TESTS OK
D1 - LIGHTS UP
R23 - BURNED
R24 - BURNED
R25 - TESTS OK
R27 - TESTS OK
R29 - TESTS OK
R 36 -TESTS OK
On hand one spare Q6, lots of Q9, lots of resistors.
Q6 - NEW
Q7 - TESTS OK
Q9 - TESTS OK
D1 - LIGHTS UP
R23 - BURNED
R24 - BURNED
R25 - TESTS OK
R27 - TESTS OK
R29 - TESTS OK
R 36 -TESTS OK
On hand one spare Q6, lots of Q9, lots of resistors.
Did R23/24 burn up AGAIN when you ran your last test last week? How many times have they burned up? And remind me what was wrong with Q6?
It looks like you know that the actives and passive parts are known good for this next round. And if you're going to fire it all up with known good parts I hope we see 20V on the PSU rails when you test that board solo.
Looking forward to your results!
It looks like you know that the actives and passive parts are known good for this next round. And if you're going to fire it all up with known good parts I hope we see 20V on the PSU rails when you test that board solo.
Looking forward to your results!
Originally Q6 was installed backwards.. New Q6 has not been tested. No power-on tests since the R23/24 burn from last week. If I power test now, the only thing different would be new resistors. Think I'll pull and test/verify Q6 before putting it it under power.
Might as well. Your hakko should make that a trivial task. Once you have tested those parts and confirmed they're all in the right orientation you should be good to fire it up.