Pioneer SWX-950 power supply wrong voltage at #11 and resistor R6 gets very hot
- Thread starter Godement
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Check Q5, the 2sc1318. They are known to fail. Thermal stress, thermal flex.
It should be replaced along with any other is this list:
https://audiokarma.org/forums/threa...ilure-prone-whatever-and-replacements.731653/
It should be replaced along with any other is this list:
https://audiokarma.org/forums/threa...ilure-prone-whatever-and-replacements.731653/
Thanks a lot Kwayde. I had already replaced 2SA720s with KSA1013s, and 2SA1318s with KSC2383YTAs. Q5 was fine upon removing and measuring - I put back a KSC2690AYSTU anyway (also Q3 is a 2690, the others are 2383s). But I still have the problem on pin #11.
Here are the voltages at transistors:
So voltages are abnormal for Q7 (all, B C E) and Q5 (C, E), Q8 (C), Q1 and Q2 (collector voltages a bit too high).
I just checked, the diodes D1 (WZ-140, replaced by 1N5244-TAP) and D2 (WZ-130, replaced by 1N4743-ATR) have correct voltage drops (14 v and 13V).
Note that replacement for WZ-130 is said to be 1N5243-TAP but it can't be found, so I used the 4743 one, also a 13 V Zener.
Resistors around those transistors were Ok last time I checked (about 1 hr ago).
Here are the voltages at transistors:
| (manual) | (replaced by) | B | C | E | B | C | E | |
| Q1 | 2SD313P-E | MGE15032 | 51,2 | 67,6 | 50,7 | 52,1 | 60,7 | 51,5 |
| 2 | 2SB507P-E | MGE15033 | -50,9 | -67,6 | -50,4 | -52,6 | -62,8 | -51,5 |
| 3 | 2SC1318-Q | KSC2383YTA | 14,7 | 51,3 | 14,1 | 15,2 | 52 | 14,6 |
| 4 | 2SA720-Q | KSA1013 | -13,5 | -50,8 | -12,9 | -14,1 | -52,6 | -13,6 |
| 5 | 2SC1318-Q | KSC2383YTA | 36,8 | 50,7 | 37,2 | 37,3 | 36,5 | 41,7 |
| 6 | 2SA720-Q | KSA1013 | -19,2 | -50,3 | -18,9 | -19,5 | -50,6 | -19 |
| 7 | 2SC1318-Q | KSC2383YTA | 0 | 36,5 | 0 | 28,7 | 35,2 | 28 |
| 8 | 2SD313P-E | MGE15032 | 14,1 | 17,1 | 13,8 | 14,6 | 23,8 | 13,9 |
| 9 | 2SD313P-E | MGE15032 | 6,1 | 17 | 6,4 | 6 | 16,5 | 5,4 |
| 10 | 2SC869-C | KSC2383YTA | 6,5 | 17 | 6,1 | 6,6 | 16,5 | 6 |
So voltages are abnormal for Q7 (all, B C E) and Q5 (C, E), Q8 (C), Q1 and Q2 (collector voltages a bit too high).
I just checked, the diodes D1 (WZ-140, replaced by 1N5244-TAP) and D2 (WZ-130, replaced by 1N4743-ATR) have correct voltage drops (14 v and 13V).
Note that replacement for WZ-130 is said to be 1N5243-TAP but it can't be found, so I used the 4743 one, also a 13 V Zener.
Resistors around those transistors were Ok last time I checked (about 1 hr ago).
Looking at the problem for the 28 volt supply at pin 11.
The emitter voltage of Q5 is close to spec that voltage feeds the collector of Q7 through R11.
The collector voltage of Q7 is present but a bit high probably due to there being no load since the output (emitter) voltage is Zero.
Check R10, R9 and especially C19. Your chart shows zero volts at the base of Q7. Either R10 is open or C19 is shorted.
Assuming Q7 is good with a base voltage of 0 you will have no voltage at pin 11.
It is possible that you have a broken or cracked trace and the reference voltage is not making it to the base of Q7.
As for R6 burning that speaks to excessive load on pins 8,9 and 10 and or pin 11. What is the voltage measured across R6?
The emitter voltage of Q5 is close to spec that voltage feeds the collector of Q7 through R11.
The collector voltage of Q7 is present but a bit high probably due to there being no load since the output (emitter) voltage is Zero.
Check R10, R9 and especially C19. Your chart shows zero volts at the base of Q7. Either R10 is open or C19 is shorted.
Assuming Q7 is good with a base voltage of 0 you will have no voltage at pin 11.
It is possible that you have a broken or cracked trace and the reference voltage is not making it to the base of Q7.
As for R6 burning that speaks to excessive load on pins 8,9 and 10 and or pin 11. What is the voltage measured across R6?
Hello and thank you very much for the advices. You were right.
The problem is solved. Some transistors were not properly oriented, diode D1 burnt down several times, 150 ohm R6 suddenly burnt (after getting very hot). In the end all output voltages were OK except for #11. Voltages at Q5 and Q7 werewrong with base volages zero. At this point I checked all the resistors and found that one, 4.7 k R10, which is between both bases of Q5 and S7, had one leg that was simply not soldered to the board !!!
That settled things and all output voltages are ok now - a tad too high (.6 to 1 V) though.
I wonder if this is due to the output voltages from the recrifier bridges are too high. Thus is a 110 volt unit that i am powering with a 220-120 volt transformer - I am in Europe and we run on 220-240 V/60 Hz
If someone knows what are the output volages at the transformer outputs for US units that would be interesting - I plan to fit the receiver with a custom made 220 V transformer.
Morale:
- check very, very carefully transistor orientation. Even though i knew somr xere ECB not BCE i made mistakes.
-if you want to renovate the power board on those receivers I would advise to just change condensers (assuming there is no other problem and it functions). Especially if you are over 70 !
- and if you need a brand new AWR-101 powerboard, write me, because i will make several new ones !
The problem is solved. Some transistors were not properly oriented, diode D1 burnt down several times, 150 ohm R6 suddenly burnt (after getting very hot). In the end all output voltages were OK except for #11. Voltages at Q5 and Q7 werewrong with base volages zero. At this point I checked all the resistors and found that one, 4.7 k R10, which is between both bases of Q5 and S7, had one leg that was simply not soldered to the board !!!
That settled things and all output voltages are ok now - a tad too high (.6 to 1 V) though.
I wonder if this is due to the output voltages from the recrifier bridges are too high. Thus is a 110 volt unit that i am powering with a 220-120 volt transformer - I am in Europe and we run on 220-240 V/60 Hz
If someone knows what are the output volages at the transformer outputs for US units that would be interesting - I plan to fit the receiver with a custom made 220 V transformer.
Morale:
- check very, very carefully transistor orientation. Even though i knew somr xere ECB not BCE i made mistakes.
-if you want to renovate the power board on those receivers I would advise to just change condensers (assuming there is no other problem and it functions). Especially if you are over 70 !
- and if you need a brand new AWR-101 powerboard, write me, because i will make several new ones !
Glad you got it sorted.
I would not worry about the voltages being a touch high. You have component tolerances at play throughout the power supply circuit.
IMO plus or minus 1 volt on regulated supplies is no big deal.
Unregulated voltages on these older units tend to be a touch higher in the US at least due to the typically higher socket voltages we now have in our homes.
I would not worry about the voltages being a touch high. You have component tolerances at play throughout the power supply circuit.
IMO plus or minus 1 volt on regulated supplies is no big deal.
Unregulated voltages on these older units tend to be a touch higher in the US at least due to the typically higher socket voltages we now have in our homes.