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Old 9th October 2017, 12:54 PM   #3541
lehmanhill is offline lehmanhill  United States
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Quote:
Originally Posted by archidea1 View Post
I replaced the filter caps and diodes over the weekend. This time I used the bulb tester when powering on. The bulb flashed for a very short moment (initial charging). No smoke, even the LED1 was lit (but only for maybe 15-20s).

I measured -9.8V on -14V rail and 0V-0.4V on 14V rail - no voltage after IC101 (LM317).
My understanding is that -14V/14V rails are for IC1 (LM318M) and the fault must be devloped there (or maybe the LM317 itself?).

I wish I could avoid resoldering LM318M - it is so small...
As Andrew said, sort out the LM317 first. I would consider replacing the other LM317 also. Since you are only getting -9.8V, it may have been damaged in the same event as the positive LM317. You might also consider D015/D205. The are cheap and easy to change and diodes can be a weak link.

The good news is that your main power supply seems to be working well now.

The reason that LED1 comes on and then goes off is likely because you are developing DC at the output. Not to surprising when one half of your LM318 power supply isn't working. Once you get things going again, it would be good to check for DC at the speaker outputs.

I also hope you don't have to change LM318, but it isn't too bad if you use a SMD removal solder like Chip Quik. Fingers crossed you don't need to.

Jac

Last edited by lehmanhill; 9th October 2017 at 12:57 PM.
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Old 9th October 2017, 04:27 PM   #3542
Joseph K is offline Joseph K  Hungary
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Question: did You check T101 /T201 for a possible position swap? orientation? I'm asking because it already happened here.
Also, check the famous R11 (1ohm) ground separator resistor. It should read exact 1ohm, if it is intact.

(and I still would do the straightest thing and swap out all active parts possibly involved..)

Ciao, George
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Old 10th October 2017, 03:10 PM   #3543
asuslover is offline asuslover  Romania
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Old 12th October 2017, 11:54 AM   #3544
archidea1 is offline archidea1  Poland
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Joseph, good point.
I didn't notice that T101 (BD139) is rotated by 180 degrees!

I resoldered both LM317 and T101 and T204 yesterday but still no success.
I measured -10V (instead of -14V) and 2V (14V).
I will try with new 14v zener diodes if I find some in my drawer but I just wonder why the other channel works ok?? I did exactly the same mistake.

Thanks again for all your help.
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Old 12th October 2017, 02:34 PM   #3545
Joseph K is offline Joseph K  Hungary
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Ok.. Now there is a hint that You might have too much current drawn at the load side.
If it tries to exceed that of the CCS (LM317) then simply the output voltage sinks.

To understand if this is the case, measure the !floating voltage drop over R101; R201.
It should be 1.2V if it's working. Maybe now it's less.
Floating means you must use a portable DMM.
I hope You controlled the value of these resistors with the circuit open?
(50ohm)

If my suspicion get's confirmed, than the LM318 is to be changed, sorry..
That is, to confirm that one should first remove the chip.
And repeat the test of the supply voltages.
Ciao, George
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Old 12th October 2017, 02:50 PM   #3546
archidea1 is offline archidea1  Poland
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Joseph, If I remember correctly I measured the voltage drop of 0.9V and it was even lower (0.6V) before the LM317 change.
Do you mean to control the resistance value of R101 and R201 when LM317 was removed?

So I understand the next step would be to remove lm318 and check -14V/14V rails.
If the voltage is correct (no load) then LM318 needs replacing?
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Old 12th October 2017, 04:33 PM   #3547
Joseph K is offline Joseph K  Hungary
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The important thing is to control that drop now, with the new transistors and LM317 in place. It could tell if the replacement works.
Also, you could also just measure the value of the 50ohm resistors in-circuit, with power supply off, naturally.

And yes, if removing the load of the chip (lm318) things get back to normal, that is telling tales..

(we are just passing through all the steps that could have been avoided with a radical clean new start.. excuse me if I insist. You had a 'major' incident, with a lot of possible consequences -- cleaning up each by each is possible-- but I don't see the enjoyment part..)

Ciao! George
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Old 12th October 2017, 05:04 PM   #3548
archidea1 is offline archidea1  Poland
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Joseph, you are right. The only problem is that I don't have all the parts required for a clean start and I just don't want to seat and do nothing...
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Old 12th October 2017, 05:10 PM   #3549
Joseph K is offline Joseph K  Hungary
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Ok, sounds reasonable..

Ciao, George
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Old 16th October 2017, 07:53 AM   #3550
archidea1 is offline archidea1  Poland
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While waiting for the new parts I removed LM318m and measured supply voltages. Everything seems to be OK. I checked also all components around IC1 (R43, C3).
I hope the replacement of LM318m will solve the issue. Will update you when I finish.
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