Re: DC detection circuit failure on Subwoofer
Ok, thanks! So 2SC2878 is ok: it has a Vebo of 25V...
Durenth
Member
Last Activity: 12-08-2020, 04:57 PM
Joined: 11-27-2020
Location: LILLE
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Last edited by Durenth; 12-08-2020, 04:38 PM. -
Re: DC detection circuit failure on Subwoofer
I think I should add that the "audio signal form speaker" is AC +/-18V
It might be important though the RC (R27/C25) circuit on the base of Q12 filters it if I understood the circuit correctly...Last edited by Durenth; 12-08-2020, 04:26 PM.Leave a comment:
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Re: DC detection circuit failure on Subwoofer
eccerr0r, if I substitute Q13 with Q12, it works fine.
But then I don't have the DC protection in the audio signal anymore.
So find myself with the problem of the replacement for Q12.
It's kind of hard to find a C2874, I only found an Ebay shop in Great Britain that have some and they're quite expensive..
I understand you say a 2sc945 will do but don't you guys think the 2SC2878, that is exactly the same as C2874 (see my post above with datasheet) except for the Collector Power Dissipation that is...Last edited by Durenth; 12-08-2020, 04:20 PM.Leave a comment:
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Re: DC detection circuit failure on Subwoofer
Hi!
First off all I'll answer Budm question:
"I think you need to report the Voltage readings of all the Base Voltages (with ref to circuit ground) of the Transistors when Q13 is in place."
Here are the voltages with Q13 removed. They're all matching the service manual references (indicated in pink):
[INDENT][/INDENT]
Here are the voltages when I put Q13 back in place:
[INDENT][/INDENT]
If I got you well Budm, you think Q13 is bad but the problem...Leave a comment:
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Re: DC detection circuit failure on Subwoofer
Unfortunately when Q13 is back on the board, it doesn't work anymore..
Q13 seems to leak between Base and Emitter and drops the voltage to a negative -0.5V at the base of Q10, thus not allowing the relay to turn on.
Voltage measurements are almost the same as the red ones in my first post..
After a lot of research, I found what I believe to be a good replacement for Q13, an other muting transistor with almost the same characteristics except for Collector Power Dissipation that is 400mW instead of 625mW on...Leave a comment:
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Re: DC detection circuit failure on Subwoofer
Hooray It works!!
I've replace the Zener with a regular 1N4001, just for testing (I also I ordered a 1N4749A diode for the long term fix).
I'm kind of busy lately so didn't have the time to go probing around the circuit, I can only say that voltage drops around the relay are now back to normal and that I can here the beautiful sound of the relay turning on when I power up the board! I also tried with audio input and the signal reaches the speaker connector.
So tomorrow I'll try Q13 again
...
Leave a comment:
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Re: DC detection circuit failure on Subwoofer
Hi!
First of all R19 is ok: 330 Ohms.
Unfortunately I can't manage to find a equivalent Zener diode for my dead MTZJ24 so I still can't power up the board and try Q10.
I believe the D4 is a Zener in order to maintain a stable Voltage drop on the coil and protect it from overvoltage.
If I'm correct with R19 being 330ohm, the voltage on the relay shouldn't exceed Rrelay*(Ub/(R19+Rrelay)) = 1100*(35/(330+1100)) = 27V.
The relay datasheet states that it can handle up to 30V, so I thought...Leave a comment:
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Re: DC detection circuit failure on Subwoofer
Thanks to you all for your replies and your help.
So D4 is short dead as Budum and Redwire suspected!
I took D4 off the board and I now have 1,050 ohms on the relay, good
I don't want to damage anything without what I understand to be a flyback diode, so I'll try to find a replacement diode on some other board before turning on the device again.
Redwire, thanks for your detailed explanations. You guys do also believe Q13 is bad if I understood everything well.
Just got back...Leave a comment:
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Re: DC detection circuit failure on Subwoofer
Hi Budm,
I shorted E and C pin of Q11 and Q10 beavior didn't change for what I can understand, I got the same readings as before Vce=10.6V on Q10 and the relay didn't trigger.
I know have :
[B][U]R19:[/U][/B]
24.5V voltage drop
[B][U]Q10:[/U][/B]
Vce=10.5V
Vbe=0.6V (0.7V when Q11 is shorted)
Vcb=9.9V
[B][U]Relay: [/U][/B]
0V voltage drop
Just for you to know, I did try the relay offboard, it's operative and starts triggering...Leave a comment:
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DC detection circuit failure on Subwoofer
Hello,
First of all sorry for my English and for my poor knowledge in transistor behavior, I'll do my best to be clear…
I have a problem with the DC detection circuit of a Panasonic 40W Subwoofer, model SW-P270.
The relay in the DC detection circuit never turns on thought there is no DC in the audio output signal.
Output signal is ok, controlled with an oscilloscope.
I found the service manual (full board schematic attached to this post) and measured the voltage as shown below, pink is the expected value indicated in the manual, red... -
Re: New Members - please post your introductions here
Hello to you all guys!
I'm Durenth from north of France, I've had a passion for electronics since I was a child but always did it on my own until now… And here I am, big day
Happy to join you guys!!!Leave a comment:
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