No, left Ch. is much higher:
"Left Ch. pin 15-20 fluctuates between 8.7 - 9.1 V, with decreasing values...."
At the office now 🙁
Setback
Well, suffered another setback 😡
I took out the big heatsink, and the 22mF caps and inspected both power amps visually, which revealed a couple of burnt resistors:
Left ch R15 (150/½W) looked busted, and it was. I only have ordinary carbon type replacement so that was what I used.
Right ch power amp Visual inspection:
R14, R15 (150/½W) looks busted.
R14 was dead, replaced with carbon type
R15 was OK, put back in.
NOTE: Left ch was the GOOD one!?
Did a complete power check on the power supply:
All values except pin 7 & 8 look good.
After this I did a complete check on all transistors on both amps for comparison, and the result is listed here:
(also attached in a zipped spreadsheet 'AWH-071-readings.zip')
I also note that the permanent signal on the right ch now is gone.
I've ordered a batch of resistors that are listed with wattage to replace those needed, and for spare stock.
But now I assume that the main issue is to get the power supply (pin 7,8) up to specs again? From what I can figure from the schematic it looks like the D5 rectifier bridge (KBPC10-02) plays a central role?
If I should try to deduct anything from this, I would guess, that the attempt to adjust center voltage caused an error in the power supply, as I believe was what happened when I did that (adjust center voltage) a couple of months ago.😕
Well, suffered another setback 😡
I took out the big heatsink, and the 22mF caps and inspected both power amps visually, which revealed a couple of burnt resistors:
Left ch R15 (150/½W) looked busted, and it was. I only have ordinary carbon type replacement so that was what I used.
Right ch power amp Visual inspection:
R14, R15 (150/½W) looks busted.
R14 was dead, replaced with carbon type
R15 was OK, put back in.
NOTE: Left ch was the GOOD one!?
HTML:
Left ch voltages:
-----------------
Pin readings
1 -62.2 (-60)
4 +23 (+23)
5 -23 (-23)
8 +62 (+60)
12 +40 (+62)* pin 7 on PSU
22 -40.7 (-62)* pin 8 on PSUDid a complete power check on the power supply:
HTML:
Power supply problems again :-(
-----------------------------------
Pin:
5 AC 45.9
6 AC 45.9
7 +41.0 (+62)*
8 -41.1 (-62)*
16 +13 (+13)
18 +13.0 (+7.5)?
19 +83.0 (+76)
20 +34.8 (+33)
22 +61.9 (+60)
23 +23.2 (+23)
27 -62.3 (-60)
28 -13.5 (-13)
Q1e +61.8 (+60.0) pin 22
Q1b +62.2 (+60.6) Q2c
Q1c +83.6 R3?
Q2e +14.1 (+14.2)
Q2b +14.6 (+14.8)
Q2c +62.3 (+60.6)
Q3e -13.4 (-13.0)
Q3b -14.0 (-13.6)
Q3c -63.1 ?
Q4e -62.4 (-60)
Q4b -63.1 ?
Q4c -84.8 ?
Q5e +13.0 (+13.0)
Q5b +13.7 (+13.6)
Q5c +26.2 ? (=Q6c)
Q6e +13.6 (+13.6)
Q6b +14.2 ?
Q6c +26.2 ? (=Q5c)After this I did a complete check on all transistors on both amps for comparison, and the result is listed here:
(also attached in a zipped spreadsheet 'AWH-071-readings.zip')
HTML:
AWH-071 Left Right Spec
q1 b r33 side 0,00 0,00 0,00
q1 c r7 side -60,60 -60,80 -60,00?
q1 e (r6) 0,60 0,56 0,60
q1 c r8 side -60,70 -60,60 -58,20
q1 b r22 side 0,00 0,00 ?
q2 e -0,56 -0,53
q2 b 0,00 0,00
q2 c 62,10 62,00 60,00
q2 b-e 0,58 0,57
q3 e -61,41 -61,30
q3 b -60,71 -61,00 -58,20
q3 c -1,50 -58,80
q3 b-e 0,64 0,67
q4 e -61,36 -61,90
q4 b -60,50 -61,90 -58,20
q4 c +12->+2.0 -0,7 - -0,8
q4 b-e 0,63 0,67
q5 e 61,20 -54,00 right is fluctuating
q5 b 60,60 -55,50
q5 c 0,67 -54,90 1,20
q5 b-e -0,62 -0,57
q6 e 0,32 -55,60
q6 b 0,67 -55,10
q6 c 43,30 40,80
q6 b-e 0,55 0,56
q7 e 0,20 -58,10
q7 b -0,15 -58,80
q7 c -44,00 -58,40
q7 b-e -0,58 -0,68
q8 e 0,02 -22,30
q8 b 0,00 -24,20
q8 c 12,80 13,00
q8 b-e -0,01 -1,88I also note that the permanent signal on the right ch now is gone.
I've ordered a batch of resistors that are listed with wattage to replace those needed, and for spare stock.
But now I assume that the main issue is to get the power supply (pin 7,8) up to specs again? From what I can figure from the schematic it looks like the D5 rectifier bridge (KBPC10-02) plays a central role?
If I should try to deduct anything from this, I would guess, that the attempt to adjust center voltage caused an error in the power supply, as I believe was what happened when I did that (adjust center voltage) a couple of months ago.😕
Not in this round - I did previously, when we were doing the power supply, before we moved on to the power amps...
I propose to move step by step again. Unplug power amps, make sure power supply gives the right voltages, then connect left channel power amp, make sure it works, then the right one.
Hi Valery.
Yes, that will be the way to troubleshoot. I'll get on it tomorrow, and post a new set of readings 🙂
Yes, that will be the way to troubleshoot. I'll get on it tomorrow, and post a new set of readings 🙂
Back again
Hi
Well, it took a little longer than I expected, and after I suffered a another setback with a damaged power supply I really lost motivation, but after I have been working on it I now have good readings on the PSU. 🙂
The problem is now the power amps - most readings are fine, but I am unable to adjust idle current
- there is no change in the voltage readings whatsoever when I turn the VR1 pots, on either channel.
If your'e still around, Valery, I would really appreciate, if you could give some more advice.
BR
Ole
Hi
Well, it took a little longer than I expected, and after I suffered a another setback with a damaged power supply I really lost motivation, but after I have been working on it I now have good readings on the PSU. 🙂
The problem is now the power amps - most readings are fine, but I am unable to adjust idle current
- there is no change in the voltage readings whatsoever when I turn the VR1 pots, on either channel.If your'e still around, Valery, I would really appreciate, if you could give some more advice.
BR
Ole
Hi Ole!
Yes, I'm here 🙂
So you have managed to make PSU working - very good basis for further troubleshooting
Did you try to measure the voltages as marked at post #4 yet?
Cheers,
Valery
Yes, I'm here 🙂
So you have managed to make PSU working - very good basis for further troubleshooting
Did you try to measure the voltages as marked at post #4 yet?
Cheers,
Valery
So glad you responded 🙂
I have a bunch of readings for trans on both channels, but here is q6b/q7b:
Q4c is also giving some strange readings:
It'll just be a short while R9, R11 & R12 - stay tuned 😉
I have a bunch of readings for trans on both channels, but here is q6b/q7b:
HTML:
Left Right Spec
----------------------------------------
q6 b 0,9 0,5 1,2 (=q5c)
q7 b 0,8 0,39 ?Q4c is also giving some strange readings:
HTML:
Left Right Spec
----------------------------------------
q4 e -61,36 -61,1 ?
q4 b -60,50 -61,90 -58,20
start at -> fades to
q4 c-left +11,5 -> +7,1 +3,0
q4 c-right + 5,5 -> +4,5 +3,0It'll just be a short while R9, R11 & R12 - stay tuned 😉
Phew - I did a un-called for discharge when I made left ch. pin 12 touch ground - I hope this isn't a serious slip? Power WAS off! and things seem normal.
HTML:
Left Right Spec
----------------------------------------
R9 0,79 0,83 0,9
R11 1,09 1,11 1,2
R12 0,82 0,88 0,9Oops 🙂 Sorry, it was pretty late here and after a long day of constant skydiving I got "switched off" 😉
OK, right channel is a bit closer to "as designed" parameters than the left one, but nothing "criminal" in both of them so far.
Now what we need to check - if you put the V-meter between collectors of Q5 and Q3 (points with 1.2V and -1.2V readings on the schematic), you should see the V changing when you rotate VR1. What are the limits of that change (min V / max V between those points)?
I assume, it is a safe test as you cannot bias the output devices properly. I normal conditions, rotating VR1 to the higher bias may result in rather high current through the output devices - just be careful.
Ah, yes - after measurements, better leave the pot in a "lower bias" position.
OK, right channel is a bit closer to "as designed" parameters than the left one, but nothing "criminal" in both of them so far.
Now what we need to check - if you put the V-meter between collectors of Q5 and Q3 (points with 1.2V and -1.2V readings on the schematic), you should see the V changing when you rotate VR1. What are the limits of that change (min V / max V between those points)?
I assume, it is a safe test as you cannot bias the output devices properly. I normal conditions, rotating VR1 to the higher bias may result in rather high current through the output devices - just be careful.
Ah, yes - after measurements, better leave the pot in a "lower bias" position.
Crashed myself, shortly after last post 😉
OK, here are some numbers:
, and I left the pots at minimum resistance, where they have been during tests, but I'm not sure if this is what you ask for, rather than minimum voltage?
OK, here are some numbers:
HTML:
q3c-q5c left 2,64 - 2,18V (Min. resist - max resistance)
q3c-q5c right 2,71 - 2,18V (Min. resist - max resistance), and I left the pots at minimum resistance, where they have been during tests, but I'm not sure if this is what you ask for, rather than minimum voltage?
OK, those look pretty fine.
I mean - minimum voltage (2,18V) as this is where the minimal bias is - just safer.
Now let's do the same measurements between pins 15 and 20 (min V and max V), and then between pins 17 and 18 (min and max again).
I mean - minimum voltage (2,18V) as this is where the minimal bias is - just safer.
Now let's do the same measurements between pins 15 and 20 (min V and max V), and then between pins 17 and 18 (min and max again).
OK, minimum voltage, that is (of course).
pretty consistant readings between the 2 channels.
HTML:
Left
--------------------------------
15-20 1,43 - 1,64
17-18 no reading 0,00 - 0,00
Right
--------------------------------
15-20 1,41 - 1,62
17-18 no reading 0,00 - 0,00pretty consistant readings between the 2 channels.
OK, good.
That means, most likely something is wrong with the output transistors.
Let's disconnect the big transistors' plugs and test the transistors with an ohm-meter.
It has to show some conductance b-c and b-e in one direction and no conductance c-e in both directions.
That means, most likely something is wrong with the output transistors.
Let's disconnect the big transistors' plugs and test the transistors with an ohm-meter.
It has to show some conductance b-c and b-e in one direction and no conductance c-e in both directions.
OK, the output transistors have been disconnected throughout these test, as per your previous advice. If trouble shooting can continue without them connected, it will a whole lot easier, since the big heatsink takes up all free space, which is nice to have when access to the various component legs is needed, particular on the left ch.
Ah, ok.
In this case, what did you mean saying you are "unable to adjust idle current"?
Idle current is actually the idle current of the output transistors... 🙄
In this case, what did you mean saying you are "unable to adjust idle current"?
Idle current is actually the idle current of the output transistors... 🙄
Maybe this just goes to show I am a completely unknowing amateur 😉
From your reply I must conclude that idle current must be adjusted with the output transistors connected...?
Should connecting the output transistors also correct the wrong reading at q4c, not giving 3 V ?
From your reply I must conclude that idle current must be adjusted with the output transistors connected...?
Should connecting the output transistors also correct the wrong reading at q4c, not giving 3 V ?
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