WEM Mk4 Copicat - low volume output

[Bushbaby]

Hi
Earlier I enquired about replacement heads at Amp Fix (https://amp-fix.com/) about replacement heads for this Copicat. I also attached a pic of the heads of my unit in order to source the correct ones. I've just received a very kind response from John Beer (the proprietor) who has indicated the following
"From what I can see I very much doubt the head condition is your problem. They could do with a good clean and maybe a light burnish with a fine wet & dry paper 600 grit would be fine. But there is some pretty serious wear on the lower edge of the tape guide on the right where the tape has been foiling it. This could be due to alignment issues with the motor mounting or possibly a bent or distorted faceplate."

Now I am stuck! Im happy to clean the heads and to look at the motor mounting. I've had a quick look at the faceplate and it doesn't appear to be bent or distorted either.

Best Regards

[Murphyv310]

Yes these are fixed heads with no adjustments.
What happens when the heads wear is the head gap widens and the wear is never even, this makes the tape wander so the azimuth alignment in effect goes off.
Of course there is a small chance there could be another fault but for me and my colleagues at the time they are reliable. 25 years down the line then yes it's possible there could be issues.

[valves4amps]

Hi Rob, there is a straight through route for the signal without echo, this should be able to be as loud as if it were not in circuit. Adjusted with the gain control, if the straight thro' signal and echo are both low volume then it will be as I've posted earlier the coupling capacitors that have dried out. If it is only the echo which is low volume then it will be the signal coming from the heads which could be either when it's recorded or playback. To determine this the echo effect should be turned off. The swell switch should turn the motor off and therefore you will not get any echo signal through, just the dry signal. If this is then still low volume your heads would appear to be ok and the fault is as said earlier dried coupling caps.

Dave

[Amie]

Rob.

I have to agree with Dave, at least don't spend money on heads until you've checked out the circuit.
If you're hearing everything at low volume its most likely the output stage around transistor 9.

Have you already checked out if the supplies are OK?

If so inject an audio signal into the signal path from output to input.
Start with the output jack.
Collector of  transistor 9.
Base of transistor 9.
Emitter of transistor 3.
Base of transistor 3.
Collector of  transistor 1 or 2 depending on the Chanel used for input, then base.
When your signal disappears check that stage for faults!
Trevor is right that they are reliable, (they were made with good components) but the design of biasing around most of the transistors is really crummy and a bad over value resistor will stop it working. The electrolytic capacitors are early suspects in the tests but mine has Philips ones and the general opinion is that they are normally above suspicion, but never assume anything. 

It could just be a broken wire or PCB track.

Sorry Rob I made my previous comments having "assumed" you had already tested the electronics, they would be cheaper to fix than bad tape heads, so....

Thanks,
Amie.

[Bushbaby]

Hi Amie
Many thanks for your reply and your recommendations. No I haven't tested the electronics just yet, I will have to remove the board from the faceplate to do this as its cramped to get test probes attached (I have tried this already).
I don't have any problem in replacing the heads (albeit the expense) but as you have indicated, I would rather tick off that the board components are all ok and functioning correctly. Im no expert at all with regards these so the inputs from member on this forum is most appreciated.
I'm also working on my WEM Custom 15 awaiting some parts to get this up and running again - fatal mistake to be doing 2 projects at the same time as well as working from home in the week!

Best Regards

Rob

[Murphyv310]

I know some have polished up heads with the likes of Solvol Autosol or even rubbing compound, wet & dry would need to be done carefully so the head face remained perfectly parallel. But don't forget that any further reduction of material off the face of the heads widens the head gap thus reducing the frequency response.
Can you confirm or otherwise that the straight through output is normal or low? If you haven't done this test then that changes things.

[Murphyv310]

The basic proceedure for service on these are to firstly check the non loop output then clean all heads and guides with IPA etc and a swab, check for head wear, check drives and guides for wear and then test with a new tape. Then fault find and repair any issues.

[Bushbaby]

All,
I spent a lot of time cleaning the heads (wiped with IPA etc) , replacing the old 1/4" jack plug (it was just a weeny bit bent) and generally cleaning the unit up (and a new tape). I tried it again today and .......it has finally got an output! It was reasonably ok for about 5 or so minutes then started to become more and more distorted. When I did clean the heads, yes indeed they are very worn. Do I assume now that it that the heads do need replacing as a initial step?

Best Regards

[Murphyv310]

Hi.
I'd assume that the heads are clogging the gap due to wear and abrasion of the tape surface. Obviously without seeing the unit in front of me I wouldn't like to give you the wrong advice as there could be more than one fault but as you say the heads are very worn so in essence they will need replacement anyway.
Good Luck.

[Bushbaby]

Hi Trevor,
It wasnt until I cleaned the heads I could see how far across they are worn. Do they really clog up that quickly - wow!

Best Regards