No sound from Ferguson 3258 tape recorder

[BillTweedy]

I finally obtained the belts for my Ferguson 3258 tape recorder and fitted them OK. I started playing a tape and I had sound from the speakers but after moving the speaker balance slider a few times the sound has disappeared.

Can I spray a switch cleaner into the switch or use a compressed air spray? Failing that do anyone still manufacture a switch?

The machine has been in my loft for quite a long time so something could have deteriorated.

Bill

[vinrads]

Yes Bill the first thing to do when an item has not been used for ages ,is to clean all the switches including the record/playback switch ,then take it from there, Mick.

[BillTweedy]

Thanks Mick, is it OK to use switch contact cleaner or compressed air or do I have to take the slider switch out?

Bill

[BillTweedy]

Update:- I've managed to get some Servisol contact cleaner but that hasn't worked.

I'm getting no sound out of both channels with the speakers and headphones. Is it possible that the slider switch for the speaker balance has lost continuity in the internals of the slider switch.

Bill

[BillTweedy]

Another update:-

I found a fuse that had blown, replaced it and I had sound again but after a short time, probably 20 seconds there was a buzzing sound from the speakers and the fuse blew again.

If there was a short circuit I would have thought the fuse would blow straight away.

Can anyone advise me what may be going wrong.

Thanks

Bill

[BillTweedy]

Here's the circuit diagram for my Ferguson 3258, can anyone point me in the right direction to what's causing FS2 to blow in the supply rectifier section.

The sound plays for a short time, then a buzzing noise comes from the speakers then the fuse blows.

The file uploaded has been reduced in quality by the forum so posting just the rectifier section.

Thanks
Bill

[ms660]

Does the fuse blow in record mode?

Lawrence.

[BillTweedy]

I haven't tried that as I need to find the microphone. Is there any reason why you mentioned that and will that isolate some of the circuitry and narrow the fault down?

Bill

[ms660]

The reason I suggested that was that looking at the schematic the +ve rail supply to the audio output transistors appears to be switched out when in record mode, if that's the case (I don't have the manual) and the fuse doesn't blow when in record mode then the audio output stage(s) might be suspect.

To try that out you don't need a microphone or a signal input.

Lawrence.

[vidjoman]

The fuse looks to be from the transformer to the rectifier and therefore the rest of the electronics. So the fault could be anywhere. Careful checking with a meter will be required without the power connected to trace where the fault, probably a faulty transistor, is located is the only way forward or you may destroy parts that still work.

[BillTweedy]

I've tried what you said Lawrence and tried recording without microphone or a signal input and the fuse does not blow. In play mode the fuse blows at around 20 seconds.

Bill

[ms660]

It's starting to sound like thermal runaway in the output transistors, it could be an output pair themselves or something else driving them to draw heavy current, if it was me I would try and isolate the +ve rail feed from both output channels individually by introducing breaks and connect a current meter in series with the breaks, one at a time, switch on, select play mode (no tape or signal) and note the current being drawn, if it starts to rise much above 10mA then switch the power off and investigate that stage, it could be a transistor or a coupling capacitor, if it doesn't rise much above 10mA then do the same test on the other channel, too hard to call yet but these tests should give a better idea.

Lawrence.

[BillTweedy]

Thank you Lawrence, I'm posting a small section of the manual showing the output of 1 channel. S1 is the Record / Play switch. In the diagram it is shown closed between contacts 2 and 3, not sure what that means as I'm not too good at reading diagrams. [S4D is the mute switch]. Point 48 is the positive rail from the rectifier.

Bill

[ms660]

Ok, looking at that snippet, between points 57 and 58 could well be a link for measuring the quiescent current (the standing no signal current) if so then disconnect there and connect a test meter in place of the link and set the meter to measure DC current, say 100mA, switch on and select play mode (no tape or signal) if it rises much above 10mA heading towards serious current then switch off straight away, disconnect the meter but leave the link open, there should be an equivalent link for the other channel, do the same test for that channel and post the findings.

Lawrence.

[BillTweedy]

Those numbers in ellipses are soldered connection points on the copper side of the PCB. There's no link there and also no corresponding point on the other channel. I'll try and find some point and unsolder a wire and create a test break in the circuit.

Also there is no S1 switch on the other channel.

Thanks
Bill

[TonyDuell]

The (+ve) supply rail to the amplifier shown is the collector of VT10, top end of R59, etc. My guess (without seeing the whole circuit diagram) is that the vertical connection to the right of the switches that is connected to the +ve rail of this amplifier goes to the +ve supply rail of the other channel amplifier.

Can Bill confirm this? Is there a second amplfier circuit for the other channel, powered from that connection.

If so, the S1 section shown will turn off both amplfiers in record mode, there is no need for a second switch.

[BillTweedy]

Hope I'm OK posting this section of the circuit diagram.

[TonyDuell]

Yes, I think I was right. VT110, etc are the amplfiier for the other channel, powered as I described.

That section of S1 (part of the record/playback switch, shown in the playback position) turns off the loudspeaker output amplifiers and turns on the erase oscillator when you switch to record mode.

[BillTweedy]

Tony, Could I ask you what the diagram means by showing the S1 switch connected across contacts 2 and 3. Does that mean it is the default position until the the Play / record key is pressed?

Thanks
Bill

[ms660]

Originally Posted by BillTweedy

Those numbers in ellipses are soldered connection points on the copper side of the PCB. There's no link there and also no corresponding point on the other channel. I'll try and find some point and unsolder a wire and create a test break in the circuit.

Also there is no S1 switch on the other channel.

Yes, I can see that clearly now, no connection points on the other channel I mean.

There isn't an equivalent S1 switch in the other channel because S1 as shown disconnects the +ve rail to both channels when in record.

Yes try and create a couple of +ve rail feed breaks (one for each channel) and do those tests.

The schematic shows S1 in the play position.

Lawrence.