Amp keeps going into protection mode

[dorke]

What is the resistance?
It doesn't agree with the:
"2 reads 48.5 ohms with Amp off, ground probe on ground speaker terminal, meter set to 200 ohms." from #54 .
All this points should be close to zero (2.5 in this dmm and probes you use),
Can you confirm this?

 

[Rick79]

What is the resistance?
It doesn't agree with the:
"2 reads 48.5 ohms with Amp off, ground probe on ground speaker terminal, meter set to 200 ohms." from #54 .
All this points should be close to zero (2.5 in this dmm and probes you use),
Can you confirm this?

Yes with the meter set to 200 ohms the resistance between S1-2 and C13 is 02.5 and resistance between S1-2 and C9 is 02.5

Resistance with Black probe on speaker ground terminal, meter on 200 ohms, S1-2 reads 11.8 ohms now

Thats weird, I dont know how i got 48.5 ohms back then.
I haven't cut any wires yet either.

 

[dorke]

O.K.
can you "play and move " the S1 connector and repeat the resistance test between S1-2 and the black speaker terminal.
Does it change the reading?

 

[Rick79]

O.K.
can you "play and move " the S1 connector and repeat the resistance test between S1-2 and the black speaker terminal.
Does it change the reading?

Ok i did, and no it doesn't change

 

[dorke]

O.k
Let's continue with cutting the wire going to pin-5.
and see if the amp goes into protect as before (no speakers).

 

[Rick79]

O.k
Let's continue with cutting the wire going to pin-5.
and see if the amp goes into protect as before (no speakers).

Ok it doesn't go into protect mode. I even tried connecting Speakers too and it stays on.

 

[dorke]

Rick,
you should check the presence of DCV on all speakers terminals before you connect them .
Since we disabled that protection mechanism.
There probably isn't any, but still do check it without the speakers.

 

[Rick79]

Rick,
you should check the presence of DCV on all speakers terminals before you connect them .
Since we disabled that protection mechanism.
There probably isn't any, but still do check it without the speakers.

Ok, i just did, theres no DCV readings

 

[dorke]

So,
Is the amp working fine now ?
High volume and clear sound?

We should continue testing.
Rick have you got a variable DCV power supply?
Or any potentiometer on hand?

 

[Rick79]

So,
Is the amp working fine now ?
High volume and clear sound?

We should continue testing.
Rick have you got a variable DCV power supply?
Or any potentiometer on hand?

No i dont have any of those. Its too early to have the larger Speakers connected and to play them real loud but with the smaller bookshelf speaker connected, its able to play loud without shutting off, with or without having the Speaker connected.

I need to get some sleep but ill try the larger speakers later today if you think its safe and get back to soon as possible with the results

 

[dorke]

Checking with the small ones is fine.
We can continue tomorrow.
Sleep well.

 

[Rick79]

Checking with the small ones is fine.
We can continue tomorrow.
Sleep well.

Thanks.

So does any of the components on the board need to be replaced?

 

[dorke]

Yes,
We just need to find out which one
It would be best to find the faulty component and fully repair the amp.

As thing are now ,the amp is working with the output DCV protection disabled.
Since you checked that there is no DCV on all outputs you can play the amp as it is(with the wire cut).
There is future risk of blowing a speaker :
If for some reason, the amp will develop a fault that will create DCV on an output .
The speaker connected to that output may be blown.


With power disconnected.
Check the resistance of R2 and R3 (DMM in ohm 200K range).
Take two measurements on each ("flipping" the probes ,4 measurements).
Repeat the test in Diode Test mode on the DMM.(another 4 measurements)
What do we get?

Have you got any resistors on hand?

 

[Rick79]

Yes,
We just need to find out which one
It would be best to find the faulty component and fully repair the amp.

As thing are now ,the amp is working with the output DCV protection disabled.
Since you checked that there is no DCV on all outputs you can play the amp as it is(with the wire cut).
There is future risk of blowing a speaker :
If for some reason, the amp will develop a fault that will create DCV on an output .
The speaker connected to that output may be blown.


With power disconnected.
Check the resistance of R2 and R3 (DMM in ohm 200K range).
Take two measurements on each ("flipping" the probes ,4 measurements).
Repeat the test in Diode Test mode on the DMM.(another 4 measurements)
What do we get?

Have you got any resistors on hand?

View attachment 26967

Ok
In 200k mode...
R2 reads 09.8
flipping the probes it reads 09.8
R3 reads 95.2
Flipping the probes it reads 96.8

In diode mode...
R2 reads 1.546
flipping the probes it reads 1.745
R3 reads 1.131
flipping the probes it reads .687

I have maybe 12 different resistors here at home.

 

[dorke]

O.K
Lets test the diodes D8-D11 ,
DMM in diode test mode and flipping the probes on each diode.

Have you got a 4.7K or about resistor?
How are your soldering skills(on PCB,any experience with that)?

 

[Rick79]

O.K
Lets test the diodes D8-D11 ,
DMM in diode test mode and flipping the probes on each diode.

Have you got a 4.7K or about resistor?
How are your soldering skills(on PCB,any experience with that)?

View attachment 26968

Ok
Meter set on diode...
D8 reads .614
D9 reads .611
D10 reads .616
D11 reads .627

With probes flipped...
D8 reads .977
D9 reads 1.266
D10 reads 1.279
D11 reads 1.261

I have two 2k resistors, an 8.2k, and a 2.2k resistor

 

[dorke]

Looks like we found our bandit...D8.

Please confirm it's measurement's (comparing to the other diodes).
If they confirm you should cut a single leg of D8 (in the middle as shown,so that if needed it would be easy to solder it back),
lift the leg a bit and recheck D8.
I hope your cutter is fine enough for that job.

 

[Rick79]

Looks like we found our bandit...D8.

Please confirm it's measurement's (comparing to the other diodes).
If they confirm you should cut a single leg of D8 (in the middle as shown,so that if needed it would be easy to solder it back),
lift the leg a bit and recheck D8.
I hope your cutter is fine enough for that job.

View attachment 26969

Ok i cut it.
D8 reads .615 and with the probes flipped, it reads nothing.

 

[dorke]

Please check on the PCB pads of D8(with the diode leg lifted as in #78).

 

[Rick79]

Please check on the PCB pads of D8(with the diode leg lifted as in #78).

The pads on D8 read .978 and reads nothing when i flip the probes