Hifi amp has stopped.

[budm]

Re: Hifi amp has stopped.

You can install the new transistors, also look at the pot setting of the one you removed, it should be set close to the original value if set wrong then you will then have too much idling current.
You should use the lamp or VARIAC otherwise you can have nice smoke if we did not catch all the bad parts.

[Portishead]

Re: Hifi amp has stopped.

Is it a bit iffy to try it with a new 2a fuse without the lamp?
And how to check the existing trimmer?
The case is melted a little. What's inside it? Can you see from the picture on the board?? Should I change it or ok for now?

[Portishead]

Re: Hifi amp has stopped.

Do you think I should change the little trimmer?

[vinceroger69]

Re: Hifi amp has stopped.

I think it a variable potentiometer maybe test the old one on ohms setting see what it reads you maybe able to set the new one then roughly before you solder it in etc .

[Portishead]

Re: Hifi amp has stopped.

Can you tell me how to check it? It has 3 legs..

[Portishead]

Re: Hifi amp has stopped.

Hi bud.
Decided to give it a shot and plug it in. The amp came on and worked perfectly for around two minutes then the internal fuse went again.

[budm]

Re: Hifi amp has stopped.

Check all four of the output transistors. How did you set the Bias pot or you did not replace it?
You need to have the lamp setup otherwise you may keep blowing parts.

[Portishead]

Re: Hifi amp has stopped.

The two new output transistors have died assuming I can just test them in situ now.

Completely different readings to the other side.
No,I have not replaced the pot.
Need to also know how to test that then.

[Portishead]

Re: Hifi amp has stopped.

Can I assume both l & r pots are supposed to have the same readings?
I take it they are left and right..

[budm]

Re: Hifi amp has stopped.

The melted one looks to be set at 12'o clock position for that bad channel.
Is the other pot set to the same position?
There are 3 legs on the pot and I believe two of the legs are electrically tied together so you can do the comparison reading between the two pots.
BTW, the pictures of the two transistor you asked on how two test them, but you did not ask about the the two little one. The picture that I marked has 4 transistors total.

[Portishead]

Re: Hifi amp has stopped.

Yes the pots do appear to be set at 12 o'clock

[vinceroger69]

Re: Hifi amp has stopped.

as per budms request and post 46 budm asked if you could test all 4 of the transistors can you retest these (all four) and post the readings as maybe also one of these are bad too.

[Portishead]

Re: Hifi amp has stopped.

Ok testing the pots. Meter on 200

Melted one - probes on back two pins reads 117.0
Probes on left rear and front 117.0
Probes on right rear and front 00.2

Other good channel -
Probes on back two pins 105.8
Probes on left rear and front 105.8
Probes on right rear and front 00.2

[Portishead]

Re: Hifi amp has stopped.

as per budms request and post 46 budm asked if you could test all 4 of the transistors can you retest these (all four) and post the readings as maybe also one of these are bad too.

Will do now

Ahhh.....stress

[Portishead]

Re: Hifi amp has stopped.

as per budms request and post 46 budm asked if you could test all 4 of the transistors can you retest these (all four) and post the readings as maybe also one of these are bad too.

side with melted pot.
140 reads
1+2 = 00.4
1+3 =1
2+3 = 1

139 reads
1+2 =01.6
1+3 =1
2+3 = 1

Other channel

140 reads
1+2 =1
1+3 =1
2+3 =1

139 reads
1+2 =1
1+3=1
2+3=1

[elrefaey_mahmoud]

Re: Hifi amp has stopped.

you should test all small driver transistors as well and all the diodes for each channel R & L

[Portishead]

Re: Hifi amp has stopped.

This is the four i've tested.

[budm]

Re: Hifi amp has stopped.

This is the four i've tested.

There are 8 total in the picture, the little 4 Transistors have purple paint and orange paint on tops, you already tested the large one next to them.
For example little Transistor T20 right next to T6.

[keeney123]

Re: Hifi amp has stopped.

Do you have any speakers connected to this Amp?

[Portishead]

Re: Hifi amp has stopped.

There are 8 total in the picture, the little 4 Transistors have purple paint and orange paint on tops, you already tested the large one next to them.
For example little Transistor T20 right next to T6.

Ok getting a little confused . I thought I was checking the 4 square shaped transistors. when you highlighted in post 46 I assumed square ones in the boxes as the huge transistors are also square.

Have I got to test the little black half round ones with purple and orange tops?