Discussion in 'Exclusively Sansui' started by lambord, Aug 15, 2018.
Oh shit!! Well you've most definitely done some damage there....
You would not normally take the back off the amplifier to set the bias, this is why they say to measure the emitters of the transistors.
When the back is on, you can't get to the emitter resistors.
LOL. I have the transistors out. I am not exactly sure what spec is on them but
1. Starts at 1.626 Mohm, then when collector and base touch its 1.382 MOhm
2. Starts at 1.620 Mohm, then when collector and base touch its 1.394 MOhm
3rd and 4th I get overload for both situations.
do you have diode test on your meter ?
Yeah, should I be using that over an ohm reading?
Would you believe me if I said all of them are good and I even pulled one out of the side I did not short for a sanity check that I was doing this right.....Because I am getting all of them to test correctly
yes i can believe anything . you sent rail voltage through the centre point . leave the outputs out of circuit for now .
most times transistors when bad will short between c and e but not always that way .. rare cases test good with a meter but bad with full power . not important right now . i am thinking driver transistors and associated resistors took a hit .
I thought I was testing the driver transistors lol. Any specific parts I should look at or are you waiting for Kevzep?
test outputs and drivers first .
Im sure this is stupid question but you mean put this back together and test the speaker outputs without dim bulb?
no use your meter to test the transistors like in that guide i posted
I already did that, like 4 posts ago. All four on the side I shorted test good and I also did 1 from the other side that I did not short just to make sure I was doing it correctly. 2 of them are NPN and 2 are PNP
how about the driver transistors etc ?
Is that just referring to all the transistors on the F-3074 driver board? And if yes, I must unsolder all of those before testing correct?
it is best to remove first yes .
You might have got lucky and just shorted out one of the main rails momentarily and not damaged any transistors. That scorch mark shows evidence of a lot of current, more than a transistor will do before it blows.
The reason Pete was asking about your testing the transistors? You obviously are not following the instructions, you test transistors with the DIODE setting on your meter. So, with you meter probes, you go, B-C, B-E, C-E, you do that twice, first time with the Red probe on B and second time with the Black probe on B.
You'll only get the voltage drop one way, So if all you get is OL, or a voltage drop as outlined, then you are all good to go.
The voltage drop will be something between 400-550mV. Most diode test functions will read 0.000mV and continuously beep to show a short.
The drivers are on the F3074 boards. TR09 and TR10, they are TO220 transistors, 2SC2238 and 2SA968 the 968 is a green one, 2238 is a black one. You can test them in circuit you don't need to remove them, but for goodness sake, be careful, and do not have the amplifier on.
These drivers are not made any more, and they are getting difficult to obtain now.
Im guessing I got lucky. I tested the 4 power transistors on board F-3114, and now I am in the process of desoldering each transistor on the drive amp board F-3074, testing, then resoldering. So far I am at transistor 5, they all have been good so far. Should I continue with all 13 on this board? Are you convinced that something broke when that arch happened?
outputs and drivers surviving is a good sign . dont have time to see if ok to run it with outputs removed to get some voltage checks and maybe listening to headphones at a low level .
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