Hifi amp has stopped.

[budm]

Re: Hifi amp has stopped.

This may help explaining what the contraption is.
http://www.vintage-radio.com/projects/lamp-limiter.html

http://www.radiomuseum.org/forum/cur...lb_tester.html
http://antiqueradio.org/dimbulb.htm

[Portishead]

Re: Hifi amp has stopped.

Goodness, I have absolutely no idea what the contraption is in post 112. I can't make that!!!

[Portishead]

Re: Hifi amp has stopped.

Ok. So are Bd140 & 139 ok?
I'll look at the lamp now

[budm]

Re: Hifi amp has stopped.

Next thing you will need is the lamp fixture so you can put the 75W Incandescent lamp in series with the load which in this case your amplifier to limit the current automatically if you still have problem in the amp, the lamp will stay on bright if there is shorted circuit, but dimly lit if things are OK, we do not want to blow your new parts.
See what I use in post 112 when I do repair works.
https://www.badcaps.net/forum/showth...t=25810&page=6

[Portishead]

Re: Hifi amp has stopped.

I hope those figures are OK.. New transistors have arrived!!

[Portishead]

Re: Hifi amp has stopped.

So. The Bd140 be = 517, bc =572
the bd139 be = 517, bc =562

[budm]

Re: Hifi amp has stopped.

Meter in Diode mode.
For PNP:
Checking B-E junction: Black probe on the BASE, Red probe on the Emitter, it should show around 0.60V.
Checking B-C junction: Black probe on the BASE, Red probe on the Collector, it should show around 0.60V.

For NPN:
Checking B-E junction: Red probe on the BASE, Black probe on the Emitter, it should show around 0.60V.
Checking B-C junction: Red probe on the BASE, Black probe on the Collector, it should show around 0.60V.

[Portishead]

Re: Hifi amp has stopped.

Ok, so am I looking for a beep or a reading ?

There are readings but unsure which way to put probes as appears to make a difference on diode mode.



One way gives steady readings then another way the readings go up and up..

[budm]

Re: Hifi amp has stopped.

OK, so they are not shorted out, now you need to use Diode mode on the meter to see if the Transistor junctions are not open between E and B, C and B. You will have to look up the spec sheet to get the pin out of those Transistors.

[Portishead]

Re: Hifi amp has stopped.

Ok,on the 200 setting (not the 200k) they don't appear to register anything.....

Actually, neither do the other ones on the other side???

[budm]

Re: Hifi amp has stopped.

i think budm wants you too test these two transistors too like you did before
Set the meter to 200-Ohm scale.
You have 3-leg device, so looking from the top you can assign left pin as pin 1, middle pin as pin 2, right pin as pin 3, then do the combination resistance testing:
1 & 2 = xxx Ohm.
1 & 3 = xxx Ohm.
2 & 3 = xxx Ohm.

just incase these are bad too

+1, the circuit is using Darligton setup for the outputs so it will not take much to destroy those transistors.

[vinceroger69]

Re: Hifi amp has stopped.

i think budm wants you too test these two transistors too like you did before
Set the meter to 200-Ohm scale.
You have 3-leg device, so looking from the top you can assign left pin as pin 1, middle pin as pin 2, right pin as pin 3, then do the combination resistance testing:
1 & 2 = xxx Ohm.
1 & 3 = xxx Ohm.
2 & 3 = xxx Ohm.

just incase these are bad too

[Portishead]

Re: Hifi amp has stopped.

The one with the blue top is Bd 139-10
The one next to the motor is Bd 140 941

The output transistors are the correct numbers also.

[budm]

Re: Hifi amp has stopped.

So I download the diagram from DIY, it shows the output transistors as
C3519 (2SC3519) and A1386 (and 2SA1386) so it uses the same outputs as your board.
You need to check those Transistors I have marked in the pictures and need their P/N.

[Portishead]

Re: Hifi amp has stopped.

[budm]

Re: Hifi amp has stopped.

OK, thanks!
I may ask for more pictures, I may have to create the virtual PCB since I do not have your board in front of me to do the reverse engineering for examples:
It will be time consuming.

https://www.badcaps.net/forum/showth...ual+pcb&page=2
https://www.badcaps.net/forum/showth...ht=Virtual+pcb
https://www.badcaps.net/forum/showth...ual+pcb&page=2

[Portishead]

Re: Hifi amp has stopped.

[budm]

Re: Hifi amp has stopped.

https://picasaweb.google.com/1178685...eat=directlink

Pictures of bottom of board...

Can you also do the top side pictures too since you have the board out so the wires are not in the way?
I download a bunch of pictures from the link you provided, I will study them to see if they are good enough for me to do the circuit tracing.

[Portishead]

Re: Hifi amp has stopped.

Ok, I've ordered the two new transistors, some 2a fuses and a potentiometer as it's a bit melted

[budm]

Re: Hifi amp has stopped.

All four read 00.6

That is normal for the Emitter resistor.