Hifi amp has stopped.

[Portishead]

Re: Hifi amp has stopped.

Do you have any speakers connected to this Amp?

Yes I did have my speakers connected to it when it failed last week.
Then, yes I had speakers connected yesterday when I retried it. Played music for 2 minutes then stopped.

[vinceroger69]

Re: Hifi amp has stopped.

budm does mean for you too check those little transitors too with the purple and orange on the top.

[Portishead]

Re: Hifi amp has stopped.

Right.will do

[Portishead]

Re: Hifi amp has stopped.

So - Testing the Orange and purple transistors starting from the bad side.

Orange called 2N5401 T.439
1+2=1
1+3=1
2+3=1

Purple called 7242N 5550
1+2=1
1+3=1
2+3=1

Orange called 2N5401 T.439
1+2=1
1+3=1
2+3=1

Purple called 7242N 5550
1+2=1
1+3=1
2+3=1

I should have just written they all say 1
Am I supposed to have the meter on the 200?

[Portishead]

Re: Hifi amp has stopped.

Just to note - Both speakers read 05.4 on the cable terminal ends.

[elrefaey_mahmoud]

Re: Hifi amp has stopped.

I suggest you should work on each channel separately,
first remove the main output transistors(C3519 & A1386) for the two channels R & L
now for one channel ( R for example ) do the following
set your multimeter to read voltage (100 or 200 ) and take readings on PCB for base emitter voltages for each output transistor (C3519 & A1386)
you should find it reads around 0.5v to 2.5v (while transistors are out of the pcb)
if readings are diff then track for the small biasing transistors for that branch and test them, if found open or short then replace them, also test the diodes (and resistors if you can)
finaly don't put the output transistors (C3519 & A1386) until you find the defected component and have the right biasing voltage readings to avoid burninig them

and do the same for the other channel.
good luck

[elrefaey_mahmoud]

Re: Hifi amp has stopped.

something important to test diode or transistor put the multimeter on diode or buzzer, and for resistors select the suitable resistor range

[budm]

Re: Hifi amp has stopped.

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?

They are all connected together (see the diagram), the little one drives the square shape, the square shape drive the large square shape on the heatsink.
The circuits are direct couple so when one component fails it can take out lots of components connected to it with it.

[Portishead]

Re: Hifi amp has stopped.

So how are the figures looking? What shall we do now? Is post 84 ok budm

[budm]

Re: Hifi amp has stopped.

So they do not show any low resistance for any leakage, now you need to test with Diode mode to test B-E, B-C junction just like what you have done on other transistor.

[Portishead]

Re: Hifi amp has stopped.

ok I think the orange 2n5401 is pnp and the purple 2n5550 is npn

so running left to right
BE = 630
BC = 616

BE = 641
BC = 633

BE = 631
BC = 618

BE = 640
BC = 632

How does that sound budm?


I cant remember if I posted up the BE / BC for the 139 & 140 transistors so -

running from the motor :-
BD 140 , BE - 513 BC 513
BD 139 , BE - 516 BC 559
BD 140 , BE - 513 BC 513
BD 139 , BE - 516 BC 559

[budm]

Re: Hifi amp has stopped.

They look OK.

[Portishead]

Re: Hifi amp has stopped.

Ok then..

[Portishead]

Re: Hifi amp has stopped.

Just thinking aloud here.... When I put the internal fuse in yesterday after replacing those large power transistors The amp and cd played music for 2 minutes or so before popping the fuse again.
I didn't actually replace the long black heat sink bar that went over the top of transistors. I don't suppose that was the cause again?

[budm]

Re: Hifi amp has stopped.

Without the bar the output transistors will get hot and get thermal run away, Transistors need to make good contact with the heatsink and you need to apply heatsink compound.
I cannot tell from the pictures as to what kind of insulator material being used on the output transistors and the heatsink.
The small 1/2 circle transistor sitting between the output transistors also need to make contact with heatsink bar.

[Portishead]

Re: Hifi amp has stopped.

The heat sink is a long piece of aluminium. I don't see any evidence of thermal paste. Either on the bar or the transistors.

[budm]

Re: Hifi amp has stopped.

That is the bar for clamping down the body of the transistor to make contact with the heat sink which is on the bottom of the unit.

[Portishead]

Re: Hifi amp has stopped.





Some kind of thin rubber tape/strip

[budm]

Re: Hifi amp has stopped.

OK, I believe they are silicone thermal transfer pads, which does not need heatsink compound, but the Transistors body must sit flat with the heatsink to get the proper heat transfer from the transistor body to the heatsink.

[Portishead]

Re: Hifi amp has stopped.

Ok. Yes they all do sit flat. Including the ones I put in last time.
So where do we go now?