Pioneer A-27 Power Supply Issue

[Watthour]

If no one has objections, then I will go on and check (and, in case, replace) D17, D18, D19, Q18, Q19 and Q21 of power supply.

Does this sound agreeable:
D17, D18, D19: 1S2473 (35V 110mA) -> 1N4148 (75V 200mA 0.5W)
Q18: 2SC945A (50V 150mA 250mW) -> KSD1616AG (60V 1A 750mW)
Q19: 2SD712 (100V 4A 30W) -> KSC2334 (100V 7A 40W) (or, at this position, sufficient if KSC2073 (150V 1,5A 25W)?)
Q21: 2SC1903 (150V 50mA 1W) -> KSC3503E (300V 100mA 7W) (or sufficient if KSC2310Y (150V 50mA 0.8W)?)


Best regards,
Frank

D17, D18, D19: 1S2473 (35V 110mA) -> 1N4148 (75V 200mA 0.5W)

Q18: 2SC945A (50V 150mA 250mW) -> KSD1616AG (60V 1A 750mW)

Q19: 2SD712 (100V 4A 30W) -> KSC2334 (100V 7A 40W):
For Q5 and Q19 the KSC2073 should be safe. For Q11 and Q20 the KSC2334 would be safer due to potential current.

Q21: 2SC1903 (150V 50mA 1W) -> A KSC2690AY would be ideal, but a KSC3503E would work as well with a lot of overhead.

 

[Japetus]

Thanks a lot.
For Q21: I still have some KSC2690AY (120V 1,2A 20W), so I'll stick to that.

 

[Japetus]

A question:
I'm currently getting out and check components as said.

I forgot to mention Q17 (2SC945A, 50V 150mA 250mW), its base is cathode-side of D19, and could be involved in this.
Have it out, tested to be OK (with component tester), but want to replace it with KSD1616AG (60V 1A 750mW).
Would this be an acceptable choice?

I ask because, with 0V at its base (as shown in circuit plan), there will be zero B-C current, so it must be of only transient use, e.g. on startup, correct?
No idea what current might flow then, so I'd better ask, if a KSC2383 (160V 1A 900mW) could give more safety and is a better choice.

 

[merlynski]

Q17 is part of the DC offset detection circuit: diff amp of Q15, logic and driver D17, D18, Q16. If dc offset is detected Q17 kills the voltage (shunts the current) that pulls in the relays by dumping the charge on the Protection circuit's delay timing cap C18.. The KS2383 may be a better choice because it Pd is 900mW, and the KSD1616's Pd is 750mW. IMHO the difference is minimal in that application. If you have a KSC2383 on hand use it. Most of the time Q17 just sits there waiting for something to do.

 

[Japetus]

Thanks for explanation - needs some repeated post readings and circuit-comparings to get it in. Transient processes are more difficult (for the non-electricians like me) than stationary .

Yes, I have some KSC2383 still at hand - I will use them.

Wish I'd have Q17's job once in a while...

 

[Japetus]

Relay clicking sequence sounds familiar and is seemingly OK, takes about 7 to 8 seconds to complete:
DBT@120W, Collector Q17 (+16.2V) -> +19.3V ?
DBT@120W, Base Q17 (Kathode D19) (0V) -> 0V
DBT@120W, Emitter Q17 (0V) -> 0V
DBT@120W, Anode D19 (-2V) -> -1.48V ?

DBT@120W, pin 10 (+0.7V) -> +0.76V
DBT@120W, pin 11(+1.6V) -> +1.55V
DBT@120W, pin 16 (+0.7V) -> +0.71V
DBT@120W, pin 14 (+24V) -> +23.2V
DBT@120W, pin 12 (+51V) -> +39.8V
DBT@120W, pin 2 (-33V) -> -32.5V
DBT@120W, pin 4 (+32V) -> +32.0V

The same without DBT:
Relay clicking-sequence is missing. Only initial click appears instantly on switching on, then nothing more:
no DBT, Collector Q17 (+16.2V) -> 0.71V
no DBT, Base Q17 (Kathode D19) (0V) -> 0V
no DBT, Emitter Q17 (0V) -> 0V
no DBT@120W, Anode D19 (-2V) -> -3.2V ?

no DBT, pin 10 (+0.7V) -> +51.6V
no DBT, pin 11(+1.6V) -> +23.5V
no DBT, pin 16 (+0.7V) -> +0.00V
no DBT, pin 14 (+24V) -> +23.4V
no DBT, pin 12 (+51V) -> +51.6V
no DBT, pin 2 (-33V) -> -32.5V
no DBT, pin 4 (+32V) -> +32.0V

I quoted post #36, to compare new with previous measurements (bottom listing is confined to values that changed significantly, were added, or might be esp. relevant for the issue).

Settings: Speaker switch to "Off", Function to "AUX".

I replaced components (as mentioned):
D17, D18, D19 (->1N4148), Q11 (-> KSC2334), Q17 (-> KSC2383), Q18 (-> KSD1616), Q19 (KSC2334), Q20 (KSC2334), Q21 (->KSC2690)
All checked to be OK (on DCA55), I also checked but not replaced Q16 (2SA733).

DBT@120W, pin 10 (+0.7V) -> +0.61V
DBT@120W, pin 11 (+1.6V) -> +0.12V
DBT@120W, pin 16 (+0.7V) -> +0.62V
DBT@120W, collector of Q17 (+16.2V) -> +19.2V (still a bit high)
DBT@120W, base of Q17 (=cathode side of D19, 0V) -> 0V
Relay clicking sequence seems to be OK, speaker output switch works the according relays.

noDBT, pin 10 (+0.7V) -> +34V
noDBT, pin 11 (+1.6V) -> +23.6 V (= pins 13, 14)
noDBT, pin 16 (+0.7V) -> +0.0V
noDBT, collector of Q17 (+16.2V) -> 0.0V
noDBT, base of Q17 (=cathode side of D19, 0V) -> +0.64V
Relay only initial click, sequence missing. Speaker output switch does not work the according relays.

Now here comes the speculative part about what happens here, if you could follow this path:

With no DBT,
- since base Q17 is permanently +0.64V, "Q17 kills the voltage (shunts the current) that pulls in the relays", and collector of Q17 stays 0V., C18 does not charge.
- subsequently base of Q21 is 0V, and therefore blocks current to flow from pin 11 through C-E of Q17
Therefore,
- pin 11 stays high at +23.6V, the output of pin 14 (and 13)
- C-E of Q18 is blocked, which blocks C-E of Q19 and thus prevents relays RL2 and RL3 on output terminal (GWX 211) to close. This fits to the observed lack of audible relay clicking sequence.
- in addition, pin 10 is high (+51.6V, = pin12)

Conclusion:
- without [edit] DBT, some DC is permanently detected, maybe barely. This does not happen when on DBT@120W (or maybe if power amp would be connected)
- Q16 checked to be OK (on DCA055), D17 and D18 have been replaced with new 1N4148

My question, if the above thoughts apply:
What to measure next to verify this assumption, or what component to check / replace?

Edit:
Maybe check Q15? If one side of it malfunctions, could it explain the observed problems?
In case, could Q15 (2SC1583) be replaced by two KSC1545F, that are closely matched on hfe, share emitter and are bonded mechanically?

 

[merlynski]

Off the DBT, on full mains voltage, what is the DCV on Power Supply AWR-176 pin 9?
This is the DC offset detection input pin, if it is not very close to 0vdc the dc offset detection may be working perfectly, preventing the relay from pulling in.
Also measure dcv on Power Amp AWH-079 pins 22 and 3, the outputs of the L and R power amps.

 

[Japetus]

Also measure dcv on Power Amp AWH-079 pins 22 and 3, the outputs of the L and R power amps.

For now, I still refrain from connecting Power Amp AWH-079, as the supply does not seem to be Ok, see below.

Off the DBT, on full mains voltage, what is the DCV on Power Supply AWR-176 pin 9?

I took values all around the complex Q16, D17, D18 and Q15 (noDBT, full mains voltage, last digit(s) unstable/drifting):

Q15 Base 1 (0V) -> -0.0042 V
Q15 Base 2 (= Pin 9, 0V) -> +0.0540 V
Q15 Collector 1 (= cath. of D18, +15.8V) -> +29.68 V
Q15 Collector 2 (= cath. of D17, +15.8V) -> +11.40 V
Q15 Emitter (-0.6V) -> -0.582

Q16 Base (= anode of D17 and D18, -16.3V) -> +12.0 V
Q16 Emitter (-15.9V) -> +12.5 V
Q16 Collector (= Q17 Base, = cath. D19, 0V) -> +0.63 V (with DBT@120W, this is 0.00V)

With these values, it could not work properly. Question is, what malfunctioning component(s) cause this.
Hope we are closing in on the failure now, find the culprit(s).

(Just to check: pin 4 (+32V) -> 32.0 V; pin 2 (-33V) -> -32.5 V)

I'll recheck D17, D18 (have been replaced with 1N4148), R6, R7, R9, R11, R12, R13 and traces on foil side.

I did already check Q16 (with DCA055) before, showed to be OK, and I did not replace it.

Would this be a suitable replacement, or shows experience a better choice:
Q16 2SA733 (50V, 100mA, 250mW) -> KSA733 (50V, 150mA, 250mW) ?

 

[merlynski]

The collectors of Q15 should be about equal voltage, since the bases are at about 0vdc and the (common) emitter is a -0..582, about where it should be. This imbalance is the problem, causing the protection circuit logic (wired OR, D17, D18) to think there is a DC offset present
Have you replaced Q15? I would use a matched pair of KSC1845F, selected primarily for matching Vbe and if possible, hFE (gain) as well.

 

[Japetus]

No, I did not replace Q15 yet.

I have about 90 pcs KSC1845F in stock, I am sure some good matching pairs according Vbe (and hFE) can be found.
Will do that next.

So Q16 B and E, being high positive instead of high negative, might just be a follow-up of Q15 collectors imbalance?
(And not, e.g., an open D17 or D18).
Anyway, D17, D18, R6, R7, R9, R11, R12, R13 and Q16 at least checked to be OK.

 

[merlynski]

If either of the collectors' voltage of Q15 drop 0.6v more negative than the base Q16 they are then forward biased, current flows through D17 or D18 and sends Q16 into conduction. The reference voltage for this is set by a voltage divider formed of R11 and R13. ERRATA: My schematic shows the emitter of Q16 connected to the voltage divider, and labeled as "-15.3v", that has to be an error on the schematic, it must be +15.3vdc for the circuit to function correctly. I just now noticed this error. When the base of Q16 is pulled negative by current through D17 or D18, the collector voltage goes positive, causes Q17 to conduct, which dumps the charge off of C18, which forces Q21 and Darlington pair Q18/Q19 into cutoff, dropping the relays.

EDIT: I missed the -15.9v in your post #48 above, you were on the right track . . .

 

[Watthour]

I see that now that you point it out. Furthermore (and by the numbers), that should be 16.2V if the supplies are -33 and +32 as the diagram shows, and the resistors are right at the spec for resistance.

 

[Japetus]

...you were on the right track . . .

Thanks, but it's not really true. I trusted (had to) the manual values, so I was unknowingly coming to wrong conclusions. My manual shows '-15.9V'.
Now it makes much more sense!

...Furthermore (and by the numbers), that should be 16.2V if the supplies are -33 and +32 as the diagram shows,

This confuses me. If I understand voltage divider (R11 and R13) correctly, should it not be about 14.8V (= -33 + 10/(10+3.6) * (32 + 33))?
I am sure you are right, but where did I go wrong on that? I'd like to learn something here.

To realize one 2SC1583, I used two KSC1845F.
Their Vbe is between 0.760 and 0.762 (area of results for repeated testing with DCA55), their hFE 341 to 344. Are these close enough?
Otherwise, I need to search more thoroughly and average their parameters over a higher number of DCA55 testing results...

 

[Watthour]

65V between the ± supplies (skewed -1V). 3,600 and 10,000Ω resistor network... I'll have to double-check the math, but it should certainly be a more positive voltage since the 3.6K is on the positive 32V supply.

 

[Japetus]

65V between the ± supplies (skewed -1V). 3,600 and 10,000Ω resistor network... I'll have to double-check the math, but it should certainly be a more positive voltage since the 3.6K is on the positive 32V supply.

It is the 10/13.6-th part of 65V up from -33V, as I understood it in simple wording. But I disregard, if a load (with its own resistance) is parallel to one R of the divider - which could be wrong.

But I am not sure, since I never learned this and as well worked only very few units in 11 yrs. - also forgetting over time what I've learned.
Therefore most times I overlook something and do it wrong. I am curious what it is now.

 

[Watthour]

You're close enough for our purposes. In either event, it is clear that the voltage should be closer to the POSITIVE supply rail if the divider network values are as indicated on the schematic.

 

[Japetus]

You're close enough for our purposes. In either event, it is clear that the voltage should be closer to the POSITIVE supply rail if the divider network values are as indicated on the schematic.

OK, that's good. I think I got it now, thank you for helping! Hope I did not waste too much of your time.

Going on next for testing with new double-KSA1845...

 

[merlynski]

It is the 10/13.6-th part of 65V up from -33V, as I understood it in simple wording. But I disregard, if a load (with its own resistance) is parallel to one R of the divider - which could be wrong.

But I am not sure, since I never learned this and as well worked only very few units in 11 yrs. - also forgetting over time what I've learned.
Therefore most times I overlook something and do it wrong. I am curious what it is now.

The difference of 1 volt in the voltage divider voltage amounts to, at worst about 1.5%. In a circuit with 5% resistors and power supplies that may vary +/-10%, IMHO, it is insignificant.

 

[Japetus]

The difference of 1 volt in the voltage divider voltage amounts to, at worst about 1.5%. In a circuit with 5% resistors and power supplies that may vary +/-10%, IMHO, it is insignificant.

Yes - sure, that is what I forgot to be aware of.

And:

SUCCESS - at least partially.

I tested again, now with only change putting in two new D17 and D18 (just to be sure) and with the 'fabricated' double-KSA1845.
Now, eventually, without DBT, all relays were clicking again, and as well I was able to switch speaker outputs again.

Here are some voltages (Speaker selector to 'OFF', Function selector to 'AUX', power amp still disconnected):
Values are quite stable, even on the 3rd or 4th digit.

Q15 Base 1 (0V) -> -3.698 V
Q15 Base 2 (= Pin 9, 0V) -> -3.675 V

Q16 Base (= anode of D17 and D18, 16.3V) -> +24 V
Q16 Emitter (15.9V) -> +32 V
Q16 Collector (= Q17 Base, = cath. D19, 0V) -> 0.000 V

pins 1, 2 (-33V) -> -32.46V
pins 4, 5 (+32V) -> +31.98 V
pin 6 (-66V) -> -66.18 V
pin 8 (+65V) -> +64.93 V
pin 10 (+0.7V) -> +0.625 V
pin 11 (+1.6V) -> +0.126 V
pins 13, 14 (+24V) -> +23.8 V
pin 16 (+0.7V) -> +0.602 V

Pin 11 is connected to one side of RL1 of pin jack assembly GWX-212, the other side goes to back to pin 14 and to relay on headphone assembly GWX-210 and output terminal (GWX-211) relays (if switch is set accordingly).
If this is not a problem, then can I assume the power supply is done, and proceed to power amp AWH-079?

 

[merlynski]

Pin 11, on which board? If you mean the AWR-176 Power Supply, that is the collector voltage of Q21, which could easily be that low if it is in saturation. It could also be shorted C-E. The listing on the schematic for 1.6v seems a bit high. If the relay is pulling in and releasing it is probably OK. Test Q21 C-E with power off to see if it is shorted. It is controlled by Q17, through R33, 100kΩ.