[DMcMahon]

Originally Posted by Boulevardier

That seems right to me. I think the tape-head demagnetiser test would indicate whether the head is working (however badly). If that gives no signal, then the path through the head and back to the input of the playback amplifier (which seems to be working) needs to be tested for DC continuity. David mentioned some hum-cancelling coils, which he said were in series with the head(s), and there is presumably some head switching somewhere to switch between the two heads for autoreverse (if I understand the system). So there is presumably more between head and amp than just a piece of co-ax cable (I don't have a circuit diagram). And I don't think we know whether he has tried both R/P heads yet.

Mike

Hi Mike,

In an earlier post I did reference that there was no sound or tape hiss in Forward and Reverse Play. The finger test on live sides of the playback heads wiring resulted in hum and only hum for the correct head depending upon whether Forward or reverse play selected, which to some extent partially checks the wiring/switching etc.

Last night did the head demagnetiser test, once again got loud hum when the probe was close to the respective head with Forward or Reverse Play selected.

For completeness I will do a full continuity resistance check of the all the associated wiring including the hum cancelling coils and the track switching.

After that will scope probe the head signals going to the electronics to see if any actual sound signal and if so, then see why it is not getting trough to the output stage, when tape is played.

Of course the playback heads could be open circuited. In that case I might still expect to get a hum signal when head live wiring touched and when demagnetiser used. So also may check the continuity of the playback heads.

I know there is a lot of press about potentially damaging heads when checking their resistance/continuity.

For diagnostic purposes I have often for a long time checked head resistances with no incidents (until last year), choosing a resistance range on DMM that gives the lowest voltage output, so generally to be honest have been historically somewhat sceptical of possible head damage.

Last year one Uher I purchased arrived with a dead right channel, after checking all the wiring connections and electronics all OK, I measured the Playback head which was open circuit. I also measured the left channel playback head which was OK of course as the left channel worked OK.

But not long afterwards the left channel died and the PB head was open circuit. Whether this was a co-incidence that the head not long afterwards died or as a direct result of checking its continuity I do not know.

The Uher heads are German Bogen which evidently can go open circuit.

So as a result of the Uher experience I am a little bit more cautious about measuring heads.

David