defective Revox B225 sings like a bird

[Bernhard]

Hi,

i have a B225 that I ( try to ) repair for a friend, when I play a piano CD it only sings like a bird "tschilp" and also there is 50Hz hum.

The 50 Hz hum looks like a bad supply voltage, supply voltages seem to be ok, +/- 12 V for analog, for the TDA1540 -5V , +4V ( taken via R lytic-C from 5V line ) and -13V ( is that enough ??? )
Havent looke with a scope though.

Already changed all SAA ICs without succsess, the RAM I don't have.

Any hint where to search ?

While we are at it, I have another bird here, my Analyzer.

On power up there is no problem, then after a few minutes it goes partly off with a "tschirp" ( I think it comes from the switching PSU ), no screen and no LEDs on plug in.
One minute later it goes on again, the processor of the plug in needs a restart of the whole machine.
And then it usually works forever.

When it is warm in the room, there isn't any problem at all, but when it is cold, it is getting more serious, fails after minutes again and again.

Looks like it fails at a specific temperature which is very ugly...

[pinkmouse]

I have no idea about your Revox, but for your analyser, I'd start with a blanket resolder. That sort of symptom is quite likely down to a dry solder joint somewhere.

[phimor]

Bernhard,
the Revox, is the noise in the output or from the transport.

Sometimes, if the focus servo is to tight the transport will 'ring' like a bell.

Otherwise its most likely the power supply. I always change all the 'litics, cures 90% of problems.

Cheers

Philippe

[anatech]

Hi Bernhard,
Did you have a look at your supplies with your 'scope first? I too have found many bad electrollytics in these. The chips would be my last resort.

-Chris

Edit: The tracking servo oscillates in the 500~600 Hz range since this is a one beam system.

[Bernhard]

The singing is not mechanical sound from the transport / laser, it comes from the audio output instead of music.

First there is the singing that gives the impression that data format is corrupted ( but that usually sounds noisier ) and ten there is 50 Hz hum.

[singa]

Hi Bernhard,
For B225, looks like the dac is kaput.Use the scope to see the output of left/right channels.I think your analyer's switching supply should be investgated also.

[singa]

Sorry,
One can't see a waveform when dac has current output so you have to go to output of analog stage, which is the opamp and if the output is distorted then you have to guess if it's the dac or opamp.

[Netlist]

Originally posted by Bernhard
50 Hz hum.

Try replacing the 100µF cap on the 33V rail in the PSU.

/Hugo

[Tube_Dude]

Originally posted by Bernhard
and -13V ( is that enough ??? )

No , it must be -18 volts... inspect the electrolytic caps in this voltage rail...

[Bernhard]

Originally posted by Tube_Dude


No , it must be -18 volts... inspect the electrolytic caps in this voltage rail...

Ah..., also the TDA data sheet says min -16,5V and max -18V,
but hey, it's aRevox