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?Testing Transistors?
- Thread starter rswojo
- Start date
I have a plugged desoldering gun. I have to remove the tip to drill it clear.
Ylli
Super Member
While you are drilling, I'll ramble....
Removing C403 will slightly detune L401, but not a lot. There is a 4700 pf cap across the coil. L401 with the caps should be resonant at 19 KHz. So we should see a clean 19 KHz at the collector of Q401. What you have seen so far strikes me as more noisy than expected an at a lower level than expected.
Removing C403 removes the load and isolates this 19 KHz amplifier. If the collector waveform is still too low and noisey, that leaves as possible faulty parts: Q401 itself (low beta), C402 (change in capacitance) or L401 (change in inductance/shorted turns).
Removing C403 will slightly detune L401, but not a lot. There is a 4700 pf cap across the coil. L401 with the caps should be resonant at 19 KHz. So we should see a clean 19 KHz at the collector of Q401. What you have seen so far strikes me as more noisy than expected an at a lower level than expected.
Removing C403 removes the load and isolates this 19 KHz amplifier. If the collector waveform is still too low and noisey, that leaves as possible faulty parts: Q401 itself (low beta), C402 (change in capacitance) or L401 (change in inductance/shorted turns).
Ylli
Super Member
Amplitude... Not sure why the screen display says >500 m. Is the 'var' knob for that channel fully CW in the detent? Is that a x1 or a x10 probe, and if x10 is the scope display recognizing it as such - knob actually set to 50 mV/div?
Can you note the time between major signal peaks? I'm seeing 5 cycles in 500 uS - that's 10 KHz, not 19 KHz. Weird.
I need to be away for 10 minutes or so.
Can you note the time between major signal peaks? I'm seeing 5 cycles in 500 uS - that's 10 KHz, not 19 KHz. Weird.
I need to be away for 10 minutes or so.
1V/div, 50uS/div, all VAR knobs fully clockwise. There is a sine wave in there that shows up clearly but not long enough to get a picture showing it.
Going back to that service manual. I upload it to a site that Mozilla Firefox has and they give me a link to the file I uploaded. I send you the link, you download and you have a better quality SM than the one you currently have.
Going back to that service manual. I upload it to a site that Mozilla Firefox has and they give me a link to the file I uploaded. I send you the link, you download and you have a better quality SM than the one you currently have.
Attachments
Ylli
Super Member
What, my pictures aren't good enough?
Ylli
Super Member
picture from post #166. I can see the graticule in this one, and it looks like the main sine wave has a period of a bit over 1 div. That's 19 KHz. Looks like the trace isn't filling the screen - might be able to fix that with the horizontal position knob.
I would have expected it to be a cleaner signal, but it is about 2 V peak-peak. At this point, I don't know if what we see is good enough or not. The next section (L402 & caps) is a pretty sharp 19 KHz filter. Let's put C403 back in and lift C406. Then let's scope the output of L402. Probably can best get at it at the top of R405.
If we don't get a clean 19KHz signal there, then we are going to need to start changing out components to check for things we can't otherwise test. Sure glad you got that parts board!
While you are gone I will ramble. When I adjust bias I try to soften the paint that fixes the pot in place with acetone, if it doesn't soften the paint and/or I get impatient I just bust it loose and adjust. I haven't been repainting the knob after I am done. Without paint holding the adjustment knob it can move and go high? I think I will check bias on my other units, adjust if it is not to spec and paint after I am done. I think Sony put that paint there for a good reason, no?
I already have Q401 somewhat desoldered. I have a transistor tester. Q401 desolder and test is the easiest and my first choice to check.
C402 is Styrol. They supposedly don't like heat. Can I safely replace that? There are 5 Styrols on this board, 4 are orange and C402 is the only gray one, hmmmmmmmm. On my parts board all the Styrols are orange.
I have a replacement coil, whether it is any good, who knows. I'd say replace the coil would be second choice, Styrol cap third.
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What, my pictures aren't good enough?
I can take what you say and find on my pictures. I'm more concerned about your old eyes.
Ylli
Super Member
Thanks, but what about my disk space. The manual I have is only 10 meg.I can take what you say and find on my pictures. I'm more concerned about your old eyes.
I have a PEAK transistor tester. I don't have the manual right here but I'm sure it will test diodes. No capicitor tester.
LOLThanks, but what about my disk space. The manual I have is only 10 meg.
Ylli
Super Member
Is C406 a polystyrene (styrol)? If looks more like a disk on the board drawing.
If you would like, you can pull the transistor, and test it. Hfe should be >100.
Those plastic caps are heat sensitive, and care must be taken when soldering/unsoldering. The positive is that their lead are usually thin and easy to solder/unsolder.
If you would like, you can pull the transistor, and test it. Hfe should be >100.
Those plastic caps are heat sensitive, and care must be taken when soldering/unsoldering. The positive is that their lead are usually thin and easy to solder/unsolder.
C403 was hard to get out and will be harder to get back in. I don't know if my old eyes can handle that tonight. How 'bout I do that tomorrow with fresh eyes and daylight and post results tomorrow morning
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Ylli
Super Member
That's one of the better testers. Mine's a cheap 'Longrunner TC1'.
C402, C404, C407, C410, C427 and C428 are all Styrols. I don't know how one can take care soldering other than being really quick. They got them in there somehow though.
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I'm getting that same feedback from SWMBO.
