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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 29th Jul 2020, 5:51 pm   #1
theholyweed
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Default Wem Copicat Mk4 repair

Hi everyone is anyone familiar with or worked on Wem Copicat tape delays? I've got one on the bench im trying to repair and its driving me mad! Its the mk4 version, the unit wasnt working at all when I got it, I changed all the electrolytics along with all the polystyrene's too, plus all the components in the oscillator board...after degausing and cleaning all the heads and fitting a new tape loop a single delay on each head could be heard, albiet very weakly with the sustain pot doing nothing to increase repeats to more than one...following this I checked all the BC108/9's which all seemed fine however since I had a drawer full of them I changed them too to no avail...Interestingly though If I bridge the 10k resistor just before the record head the unit seems to work as intended with the sustain control and the extra repeats however the delays are distorted.....
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Old 29th Jul 2020, 6:37 pm   #2
theholyweed
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Default Re: Wem Copicat Mk4 repair

https://ibb.co/mcm73bd
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Old 29th Jul 2020, 8:08 pm   #3
mole42uk
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Default Re: Wem Copicat Mk4 repair

I wonder if you followed a diagnostic procedure? Changing all the components hasn’t repaired it, so there must be something else that you missed. All the Copicats that I’ve dealt with had simple faults…
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Old 29th Jul 2020, 9:41 pm   #4
theholyweed
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Default Re: Wem Copicat Mk4 repair

The unit wasnt working at all before I recapped the whole unit and rebuilt the oscillator pcb, after that its started to pass a signal and show signs of life...the problem im describing was exactly the same before replacing all the transistors...
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Old 30th Jul 2020, 2:17 pm   #5
unitelex
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Default Re: Wem Copicat Mk4 repair

Assume you have checked the power rails are reasonable, the 1st stage gets regulated supply via 18V Zener so that should be circa 18V and the rectified secondary should be 20 something volts or so.

Worth comparing performance between the two inputs, if no appreciable difference then the problem would seem to be around Q3 Q4 stages.

Also check the bias oscillator (2x BFY51) is reasonable amplitude and frequency

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Chris
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Old 30th Jul 2020, 5:38 pm   #6
mole42uk
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Default Re: Wem Copicat Mk4 repair

You say it didn’t work at all. Did the motor run? Power ‘on’ lamp light up? Any clicks through the output when pressing switches? Any noise from the gain controls? Did you check that the 10k resistor was actually 10k?
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Old 30th Jul 2020, 5:59 pm   #7
Trevor
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Default Re: Wem Copicat Mk4 repair

Another thing to look for is the actual tape I can remember having problems back in the day with non Wem tape So try a few different types if you are making your own. Also ensure the tape is the correct way round.

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