Hi everyone and thanks in advance for suggestions.
New to all this, so happy to accept any type of feedback.
I’ve purchased a faulty Sony WMSP85 active subwoofer. The unit powers on but no sound comes out.
I’d read on another thread that one of the ICs (STK-404-130S) fails very regularly, so I’ve desoldered that and replaced it to no avail.
I’ve also replaced 3 capacitors that looked like they’d burst, and I must confess I am probably responsible for some or all of these, because I think I created a short while voltage testing the old STK-404-130S.
When replacing the capacitors, I had come under the impression that the capacitance and type (film in this case) need to match however the voltage rating can be different, so long as it’s at least as high as the capacitor being replaced. Please correct me if I’m wrong on this. For reference, they were C203, C204 and C208 from the data sheet.
I’ve taken voltage readings across the PCB where the datasheet specifies the expected voltages, and they do seem to be a bit out.
The voltages across the STK-404-130S are as follows, with the data sheet expected voltage in brackets:
1: 0v (0)
2: 0.25v (0.3)
3: 0.14v (0.1)
4: 0.15v (0.1)
5: 0v (0)
6: -51.8v (-42)
7: 11.9v (12.3)
8: 0.64v (1.1)
9: -1.1v (-1.1)
10: -51.9v (-42.5)
11: 51.9v (42.5)
12: 0v (0)
13: 0v (0)
There’s 2 other smaller ICs (NJM4565DD), with voltages as follows:
IC202:
1: 40mv (0)
2: 40mv (0)
3: 23mv (0)
4: -11.9v (-12.3)
5: 5mv (0)
6: -1.8mv (0)
7: 11.6mv (0)
8: 11.97v (12.3)
IC203:
1: 5.8mv (0)
2: 5.9mv (0)
3: 5.2mv (0)
4: -11.94v (-12.3)
5: 34.2mv (0)
6: 35.3mv (0)
7: 35.6mv (0)
8: 11.93v (12.3)
The data sheet also has expected voltages for each of the 5 other transistors on the circuit, so I’ve tested these and they are as follows, again with expected voltage in brackets:
Q501
B: 0v (-3.8)
C: 0v (21.5)
E: 0.5v (not specified)
Q502
B: 0v (0.7)
C: 52.2v (1.3)
E: 0v (not specified)
Q503
B:0v (not specified)
C: 0v (21.5)
E: 0v (0)
Q504
B: 0v (0)
C: 0v (21.5)
E: 0v (not specified)
Q505
B: 0.25v (0.3)
C: 11.96v (12.3)
E: 0.014v (0)
Thanks for any input!
Cam.
New to all this, so happy to accept any type of feedback.
I’ve purchased a faulty Sony WMSP85 active subwoofer. The unit powers on but no sound comes out.
I’d read on another thread that one of the ICs (STK-404-130S) fails very regularly, so I’ve desoldered that and replaced it to no avail.
I’ve also replaced 3 capacitors that looked like they’d burst, and I must confess I am probably responsible for some or all of these, because I think I created a short while voltage testing the old STK-404-130S.
When replacing the capacitors, I had come under the impression that the capacitance and type (film in this case) need to match however the voltage rating can be different, so long as it’s at least as high as the capacitor being replaced. Please correct me if I’m wrong on this. For reference, they were C203, C204 and C208 from the data sheet.
I’ve taken voltage readings across the PCB where the datasheet specifies the expected voltages, and they do seem to be a bit out.
The voltages across the STK-404-130S are as follows, with the data sheet expected voltage in brackets:
1: 0v (0)
2: 0.25v (0.3)
3: 0.14v (0.1)
4: 0.15v (0.1)
5: 0v (0)
6: -51.8v (-42)
7: 11.9v (12.3)
8: 0.64v (1.1)
9: -1.1v (-1.1)
10: -51.9v (-42.5)
11: 51.9v (42.5)
12: 0v (0)
13: 0v (0)
There’s 2 other smaller ICs (NJM4565DD), with voltages as follows:
IC202:
1: 40mv (0)
2: 40mv (0)
3: 23mv (0)
4: -11.9v (-12.3)
5: 5mv (0)
6: -1.8mv (0)
7: 11.6mv (0)
8: 11.97v (12.3)
IC203:
1: 5.8mv (0)
2: 5.9mv (0)
3: 5.2mv (0)
4: -11.94v (-12.3)
5: 34.2mv (0)
6: 35.3mv (0)
7: 35.6mv (0)
8: 11.93v (12.3)
The data sheet also has expected voltages for each of the 5 other transistors on the circuit, so I’ve tested these and they are as follows, again with expected voltage in brackets:
Q501
B: 0v (-3.8)
C: 0v (21.5)
E: 0.5v (not specified)
Q502
B: 0v (0.7)
C: 52.2v (1.3)
E: 0v (not specified)
Q503
B:0v (not specified)
C: 0v (21.5)
E: 0v (0)
Q504
B: 0v (0)
C: 0v (21.5)
E: 0v (not specified)
Q505
B: 0.25v (0.3)
C: 11.96v (12.3)
E: 0.014v (0)
Thanks for any input!
Cam.
Firstly you need to understand how the power supply works, then take some basic voltage checks.
From your checks I note that Q502 has 52volts on its collector; correct for now when powered off.
However Q501 has zero in the collector. What does that tell you, ...... yes the mains transformer could be open circuit/bad connection; check connector pins 2 & 3 for AC supply of approximately 20volts or so. Q501 must be turned off to allow the main relay to power the system. That is acheived by feeding a reverse bias on its base from the diode and two resistors from the AC off the transformer winding pin3. Maybe Q501 is faulty ... have a look before throwing more parts at it. Why is there no voltage on its collector ... that is the burning question.
NEVER use a parts cannon and throw stuff in there without basic testing and understanding first. You will never learn how to fault find and repair successfully if you do.
From your checks I note that Q502 has 52volts on its collector; correct for now when powered off.
However Q501 has zero in the collector. What does that tell you, ...... yes the mains transformer could be open circuit/bad connection; check connector pins 2 & 3 for AC supply of approximately 20volts or so. Q501 must be turned off to allow the main relay to power the system. That is acheived by feeding a reverse bias on its base from the diode and two resistors from the AC off the transformer winding pin3. Maybe Q501 is faulty ... have a look before throwing more parts at it. Why is there no voltage on its collector ... that is the burning question.
NEVER use a parts cannon and throw stuff in there without basic testing and understanding first. You will never learn how to fault find and repair successfully if you do.
I would look around there as well.
The emitter should be 0V (ground) but you show 0.5v. Could you have B and E mixed up in your readings?
Check C501 and check that R501 and R500 are OK and check the diode D501 is not leaky.
Also check that R503 is OK.
All resistors will need isolating to get a good reading.
Hi Jon & Mooly,
thanks for the great tips.
Regarding power supply, I got the following values at CN402:
1: 37.7v
2: 0v
3: 0.4v
4: 21.7v
5: 0v
6: 22.1v
The resistors (R501, R502, R503, R504) all appear fine and match their expected ohms. I removed them, tested them and put them back in.
D501 also appears good - In diode mode I get OL in one direction and 564 in the other (is this mv?).
I haven't tested any caps. I only have a multimeter but I'm a bit unsure how to do it.
However I think all 5 transistors (Q501, Q502, Q503, Q504 and Q505) are all bad. I've removed them and got the following readings in diode mode:
I also built the following circuit, and none of them behaved correctly when placed in it. An LED is meant to light up when the button is pressed - if the transistor is good. I'm sure you would have figured that out 😊
I'll replace the faulty transistors and see where it gets us.
Thanks again,
Cam.
thanks for the great tips.
Regarding power supply, I got the following values at CN402:
1: 37.7v
2: 0v
3: 0.4v
4: 21.7v
5: 0v
6: 22.1v
The resistors (R501, R502, R503, R504) all appear fine and match their expected ohms. I removed them, tested them and put them back in.
D501 also appears good - In diode mode I get OL in one direction and 564 in the other (is this mv?).
I haven't tested any caps. I only have a multimeter but I'm a bit unsure how to do it.
However I think all 5 transistors (Q501, Q502, Q503, Q504 and Q505) are all bad. I've removed them and got the following readings in diode mode:
| Q501 | Q502 | Q503 | Q504 | Q505 | |
| EC | 695 | 1585 | 694 | OL | 691 |
| CE | OL | OL | OL | OL | OL |
| EB | 723 | 675 | 695 | OL | 696 |
| BE | OL | OL | OL | OL | OL |
| BC | OL | 681 | 705 | 663 | 696 |
| CB | OL | 685 | 1000 | 684 | 680 |
I also built the following circuit, and none of them behaved correctly when placed in it. An LED is meant to light up when the button is pressed - if the transistor is good. I'm sure you would have figured that out 😊
I'll replace the faulty transistors and see where it gets us.
Thanks again,
Cam.
Its great you are interested enough to look at this 🙂
Here's my take on it all...
All those transistors are in a low power configuration and the only route for any real current flow is via the relay... so damage to them is extremely unlikely. Although a single transistor may have a fault it would be just that, a one off...
Q504 has internal biasing resistors and can not be tested on a meter in the normal way.
The circuit you show for testing transistors is very basic but should work up to a point. If you short C to E one of the LED's should light. If you reverse the battery (that is all the switch does) the other LED should light.
The resistor values are very low and particularly so for modern LED's and high gain transistors. The 390 ohm could easily be increased to at least 1k and the 1k to 10k.
Back to your circuit.
The voltages on CN402 are all AC voltages, not DC so make sure your meter is on the correct range. Your earlier readings showing -51 and +51 volts DC and -11 and +11 volts on the IC's tell us these AC voltages are going to be OK. Measure ALL these voltages from a known good ground point anywhere on the board.
Working back from these - and + 51 volts DC means you should see around 36 volts AC on pins 1 and 3 of CN402. The voltages on pins 4 and 6 we can't determine accurately because the DC supplies you measured are regulated and we have no way of knowing the 'raw' values other than to say they are most likely OK (otherwise the -/+11 you measured would be incorrect)
Quick checks you can do 🙂
Remove Q503 and Q504 and see if it all works.
If it doesn't then leave them removed and now also remove Q501. Does it work now?
Maybe do this one last but given the DC voltages on the main power amp chip are OK (specifically 0 volts on pins 12 and 13 meaning no DC offset) you could apply a short across C and E of Q502 and the relay should engage and the amp play. That simply applies power to the relay and it should pull in immediately.
Here's my take on it all...
All those transistors are in a low power configuration and the only route for any real current flow is via the relay... so damage to them is extremely unlikely. Although a single transistor may have a fault it would be just that, a one off...
Q504 has internal biasing resistors and can not be tested on a meter in the normal way.
The circuit you show for testing transistors is very basic but should work up to a point. If you short C to E one of the LED's should light. If you reverse the battery (that is all the switch does) the other LED should light.
The resistor values are very low and particularly so for modern LED's and high gain transistors. The 390 ohm could easily be increased to at least 1k and the 1k to 10k.
Back to your circuit.
The voltages on CN402 are all AC voltages, not DC so make sure your meter is on the correct range. Your earlier readings showing -51 and +51 volts DC and -11 and +11 volts on the IC's tell us these AC voltages are going to be OK. Measure ALL these voltages from a known good ground point anywhere on the board.
Working back from these - and + 51 volts DC means you should see around 36 volts AC on pins 1 and 3 of CN402. The voltages on pins 4 and 6 we can't determine accurately because the DC supplies you measured are regulated and we have no way of knowing the 'raw' values other than to say they are most likely OK (otherwise the -/+11 you measured would be incorrect)
Quick checks you can do 🙂
Remove Q503 and Q504 and see if it all works.
If it doesn't then leave them removed and now also remove Q501. Does it work now?
Maybe do this one last but given the DC voltages on the main power amp chip are OK (specifically 0 volts on pins 12 and 13 meaning no DC offset) you could apply a short across C and E of Q502 and the relay should engage and the amp play. That simply applies power to the relay and it should pull in immediately.
Hey Mooly,
thanks for the detailed response!
So if I'm reading correctly, are you in doubt that the transistors are faulty at all? Am I testing them wrong? Could I have just fried them removing them from the PCB?
I'll give it another go with Q503 and Q504 removed as you've suggested and see what becomes of it.
A side question, given I only have a multimeter, what other kit would you use to test a device like this?
Cheers
Cam.
thanks for the detailed response!
So if I'm reading correctly, are you in doubt that the transistors are faulty at all? Am I testing them wrong? Could I have just fried them removing them from the PCB?
I'll give it another go with Q503 and Q504 removed as you've suggested and see what becomes of it.
A side question, given I only have a multimeter, what other kit would you use to test a device like this?
I've had a lifelong admiration for people who can repair electronics, I figured it's time to up my game a bit 🙂
Cheers
Cam.
It is always possible to have a single random failure on a transistor but it is it also very very rare on low power stuff like this. I suspect something amiss with the testing (and unlikely you have fried them) but lets make sure. Lets test the tester 🙂
If you take the tester above you built and switch it on with NO transistor fitted the LED's should be off. Make sure the switch is in NPN position and measure from the battery negative terminal to the collector point. You should read plus 9 volts. The Base point should have zero volts. LED off. If you press the Test button the Base point should rise to 9 volt and the LED still be OFF.
If that is OK then connect any of those transistors to the tester but only connect the collector and emitter. The LED should be OFF.
Make sure you are identifying the pins correctly on the transistor. Data sheets are here:
DATA SHEETS
Just search for the device numbers. Enter just the main part such as 2SC2784 and ignore any letters after that.
Now connect the Base. The LED should still be off. Press the button and it should light.
At this point a decent meter is all you need.
If you take the tester above you built and switch it on with NO transistor fitted the LED's should be off. Make sure the switch is in NPN position and measure from the battery negative terminal to the collector point. You should read plus 9 volts. The Base point should have zero volts. LED off. If you press the Test button the Base point should rise to 9 volt and the LED still be OFF.
If that is OK then connect any of those transistors to the tester but only connect the collector and emitter. The LED should be OFF.
Make sure you are identifying the pins correctly on the transistor. Data sheets are here:
DATA SHEETS
Just search for the device numbers. Enter just the main part such as 2SC2784 and ignore any letters after that.
Now connect the Base. The LED should still be off. Press the button and it should light.
At this point a decent meter is all you need.
Oopsie. I have misread the data sheets. I actually find them slightly misleading, as they've got the front-on view above the end-on view, and I assumed the pins corresponded, whereas I should have checked the shape of the enclosure on the end-on view, which I've done now.
However, when I was doing my in-PCB testing, I do think I still got them basically right as I was going by the PCB's data sheet which specifies where the emitter is.
Anyhoo, they now test correctly within the test circuit. I had rigged up my button incorrectly as well. I followed the steps you described. Thanks for that!
So I'm now confused, the table above where I'd tested them all with my multimeter in diode mode and got strange results, is that all null and void? I thought transistors tested basically like 2 diodes next to each other..so for example, Q502, when I tested across the base and collector (which I now realise will actually be emitter and collector), I got current in both directions. Do I just forget all that and listen to the results of my test circuit.
I guess the wash up of all this is that I should put the transistors all back on the PCB and keep testing? I'll make sure to put them back in the right configuration 😀
Good to hear.
Right now I'm further confused. On the circuit board diagram, where transistors are seated (eg Q501), does the "E" not signify where the emitter goes? Because it appears connected to D501, R502 and C501, however the schematic shows the base should connect to these.. I'm missing something obviously 🤔
This might also explain why I got weird voltage results (eg 0.5v on Q501 emitter)
This might also explain why I got weird voltage results (eg 0.5v on Q501 emitter)
Welcome to the real world of service and repair 🙂 The board layout markings are indeed incorrect. The emitter of Q501 should go to ground. What is marked E on the board is in fact the base.
Yes, refit them and then we work off voltage measurements, however seeing as you have them removed you could just refit Q502 which is the relay coil driver and leave all the others out for now.
The relay should close just quickly looking at the circuit with a simple delay at switch on introduced by C502 charging via R503. In other words it should work. It might be wise to disconnect the speaker by pulling plug CN301 first and then just see if the relay pulls in OK. If it does you can recheck that the DC offset is still zero (no DC voltage on CN301... do not accidently short the connectors) and if it is OK then the unit should play music if you want to test it.
If it is OK then disconnect the speaker before turning it off.
Then refit Q501 and see if the unit still works normally.
HI Mooly,
So I've had a brief glorious period of about 5 minutes where it appeared the speaker was working. I was so nearly there.
Before I read your post suggesting to add the transistors back gradually, I'd reinserted them all. I did some testing and realised there was a broken trace. I don't believe this was pre-existing, I believe I damaged one of the solder holes removing a resistor to test previously. Anyway, I've repaired that, and was doing further voltage testing.
I don't recall what specifically I was testing, because the moment didn't seem important to me until afterwards, but as I tested voltage somewhere, I heard a simultaneous click, and after this, all my voltages seemed to correspond very closely to the data sheet. I assume the click was the relay doing it's thing?
I even had a very satisfying moment testing pin 3 on the large IC which I think is signal in, when the speaker made that buzzing sound a speaker makes when you're trying to plug it in while it's on. When I turned the speaker off, the clicking sound happened again. I turn the speaker back on, clicking sound and still operational, still getting that buzz when testing pin 3.
Then, and I forget exactly why I did this, I drained the residual voltage from C404. I've done that previously with a 1k ohm resistor to make the board safe before removing it to do further testing. However immediately after doing this, the speaker has returned into it's previous non-operational state.
I now happen to be getting all of 17mv across the collectors of Q501, Q503 and Q504.
Do those events suggest anything in particular?
Thanks,
Cam.
So I've had a brief glorious period of about 5 minutes where it appeared the speaker was working. I was so nearly there.
Before I read your post suggesting to add the transistors back gradually, I'd reinserted them all. I did some testing and realised there was a broken trace. I don't believe this was pre-existing, I believe I damaged one of the solder holes removing a resistor to test previously. Anyway, I've repaired that, and was doing further voltage testing.
I don't recall what specifically I was testing, because the moment didn't seem important to me until afterwards, but as I tested voltage somewhere, I heard a simultaneous click, and after this, all my voltages seemed to correspond very closely to the data sheet. I assume the click was the relay doing it's thing?
I even had a very satisfying moment testing pin 3 on the large IC which I think is signal in, when the speaker made that buzzing sound a speaker makes when you're trying to plug it in while it's on. When I turned the speaker off, the clicking sound happened again. I turn the speaker back on, clicking sound and still operational, still getting that buzz when testing pin 3.
Then, and I forget exactly why I did this, I drained the residual voltage from C404. I've done that previously with a 1k ohm resistor to make the board safe before removing it to do further testing. However immediately after doing this, the speaker has returned into it's previous non-operational state.
I now happen to be getting all of 17mv across the collectors of Q501, Q503 and Q504.
Do those events suggest anything in particular?
Thanks,
Cam.
I think C404 and discharging that is coincidental.
This voltage keeps Q501 off. What voltage do you measure on the base lead of Q501?
Those voltages all tell us you have no base voltage to turn on Q502 which is the relay driver. This is why fitting the transistors in the order I mentioned would help narrow things down in a logical sequence, however first thing to check now is that you have the minus 3.8 volts on the base of Q501. Measure on the pin of the transistor itself.
This voltage keeps Q501 off. What voltage do you measure on the base lead of Q501?
Right now I’m getting +0.7v at Q501’s base.
Literally, as I wrote that, the relay clicked and I’m now getting -3.2v there as well as 25v for the collectors mentioned above and pin 3 is making the speaker buzz for me.
Assuming the speaker is behaving itself, do you normally just test by plugging back into a stereo, or some other method?
Cheers
Cam.
Literally, as I wrote that, the relay clicked and I’m now getting -3.2v there as well as 25v for the collectors mentioned above and pin 3 is making the speaker buzz for me.
Assuming the speaker is behaving itself, do you normally just test by plugging back into a stereo, or some other method?
Cheers
Cam.
It’s plugged in and thumping!
Thanks so much for your detailed help! Many good lessons learned.
Cam.
Thanks so much for your detailed help! Many good lessons learned.
Cam.
What was the problem though?
That negative voltage should be present at all times the unit is on.
If that supply was missing and then suddenly appeared there is a problem somewhere. Cap C501 could be deteriorated and low in value or there could be a simple dry joint in that area. Its not impossible for D501 to faulty too.
That negative voltage should be present at all times the unit is on.
I'd love to be able to tell you, but I don't know exactly. I'm conscious of Mooly's comments that something still might not be right inside, but unless it plays up again, I probably won't be fiddling around again for the moment.
What I can tell you is what I've changed so far, whether or not any of it has made a difference. I should point out my experience in repairing electronic items consists of this speaker and 3 other items. I'm a noob, so take that into account.
- IC301 has been replaced
- C203, C204 and C208 have been replaced. I probably caused at least one of them to be damaged.
- I've repaired a broken pin hole on the lower voltage side of R503, which again I think I might have caused.
I'll keep the thread updated if I need to have another look at the unit.