Philips FR-740 working but no audio output

[R_J]

Re: Philips FR-740 working but no audio output

It should'nt be hard to find a transitor to use for now, almost any pnp rated higher than 60v should work.
So with that transistor out of circuit do you have audio out of the speakers?
did the voltage on 7310 (C) drop a bit lower from before?
With that transistor out of circuit, any comand from the front panel should have no effect on turning the amp ic's on or off, so if there still is no audio (and you have it at the stk inputs) then that voltage on the CCC line must still be too high

[seve91]

Re: Philips FR-740 working but no audio output

replaced 7309, 7304, 7310, 7902, 7909. same voltages remain.
Could be a bad capacitor somewhere? Why the voltage is too high?

[seve91]

Re: Philips FR-740 working but no audio output

It should'nt be hard to find a transitor to use for now, almost any pnp rated higher than 60v should work.
So with that transistor out of circuit do you have audio out of the speakers?
did the voltage on 7310 (C) drop a bit lower from before?
With that transistor out of circuit, any comand from the front panel should have no effect on turning the amp ic's on or off, so if there still is no audio (and you have it at the stk inputs) then that voltage on the CCC line must still be too high

No still no audio voltage on CCC too high, don't know why. Without transistor, C of 7310 is -37.7V.
Tried replacing cap 2350 without success

[R_J]

Re: Philips FR-740 working but no audio output

I don't know why either, what ever it is effects both amp ic's correct? as both are turned off.
What are the voltages on transistor 7261 & 7260 ?

[seve91]

Re: Philips FR-740 working but no audio output

sorry friend, i've just reassembled it. I give up.
Too much time wasted, and can't find a solution still.
Thanks to you for all your kindness and patience, your tips were useful to improve my troubleshooting skills.

[R_J]

Re: Philips FR-740 working but no audio output

Maybe put it away for a while and come back to it later, sometimes a break is needed and when you look at it another time the answer may come easier. It is likely something simple that is being over looked.
I also looked at the service manual for the FR975, it is very similar and a lot clearer to read, although the voltages are a bit different (slightly higher for more power) they are very close

[seve91]

Re: Philips FR-740 working but no audio output

Maybe put it away for a while and come back to it later, sometimes a break is needed and when you look at it another time the answer may come easier. It is likely something simple that is being over looked.
I also looked at the service manual for the FR975, it is very similar and a lot clearer to read, although the voltages are a bit different (slightly higher for more power) they are very close

i don't know...maybe you're right.
For sure I don't have so much experience... I go on with attempts.
The amplifier is not mine, the owner is a friend.
If she wants to bin it, then i will take it back.

[seve91]

Re: Philips FR-740 working but no audio output

Hi everyone, due to Lockdown here in Italy, I decided to disassembly the Philips FR740 again to find out the issue. Hope to fix it this time.

[seve91]

Re: Philips FR-740 working but no audio output

IC7412 got 2 faulty output. Replaced, now i have 4.9V on AMP LR LINE, but still no sound.
On the C of 7309 i have -21V instead of -34.5V, and I have -40V on C of 7304, and I have almost -40V on pin 14 CCC instead of -33.5V (C of 7310).

HST & DC Protection Circuit seems to be good.

Very low voltages on 7909 and 7902.
All those transistor have already been replaced.
Any advice?

[seve91]

Re: Philips FR-740 working but no audio output

Fixed! -VPl was missing, found an high resistance on 3901 (should be 47ohm). Replaced and now seems to be working good.

Usually when a resistor is broken, i can see a black spot or something. This one was perfect like new, and i can measure an high resistance instead of the usual open circuit.

Thank you everyone very much for your help!

[R_J]

Re: Philips FR-740 working but no audio output

Good to here it's working, If that's a fusable type resistor, it might not show that it is bad.