17th Dec 2014, 9:41 pm | #81 |
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Re: WEM Copicat Custom
You can actually see the label on the transformer in post #65.
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17th Dec 2014, 9:46 pm | #82 | |
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Re: WEM Copicat Custom
Quote:
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17th Dec 2014, 9:58 pm | #83 | |
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Re: WEM Copicat Custom
Quote:
Weird mix of English and French I think but I'm not sure they have used the 220v, I think red is 240v, so it's maybe putting out less than it should be? I'm a bit confused by the markings, there are 4 wires for the input, black red yellow and violet / purple. On the label these must correspond to "sw" "-gb" "vt" and "-rt", which are negative / 220v / 230v / 240v...but I'm not sure how except that "v" could be "violet" and "r" could be "rouge" (red). The ones used are black and red. See what you make of the photo, sorry it's not clearer than that. You can also see that its a bit burnt. The replacement cap was rated at 600v! |
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17th Dec 2014, 10:02 pm | #84 |
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Re: WEM Copicat Custom
Looks more German than French to me, e.g. "rt." = rōt, i.e. red.
I think "sec" in this case refers to the secondaries. Nick. |
17th Dec 2014, 10:05 pm | #85 |
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Re: WEM Copicat Custom
The primary winding has a zero volt connection and taps for 220V, 230V and 240V mains supplies. The abbreviations obviously indicate colours, but I'm not sure it's French. Could it be Swartz for black?
The HT winding is obviously the red wires and the green wires the HT winding. 250V from the secondary won't do the do the Copicat any harm at all. EDIT. German colours:- black schwarz (sw) red rot (rt) So you transformer is wired for a 230V AC input. violet (vt) yellow gelb (gb) green grĂ¼n (gn)
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17th Dec 2014, 10:07 pm | #86 |
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Re: WEM Copicat Custom
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17th Dec 2014, 10:07 pm | #87 |
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Re: WEM Copicat Custom
Ah yes silly me, must be German.
So strictly speaking for use in France (220v) it should be the yellow and black used, not red and black, but you seem to be saying that wouldn't be much of a problem? |
17th Dec 2014, 10:17 pm | #88 |
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Re: WEM Copicat Custom
I don't for one minute imagine that using the 230V tapping rather than the 220V one will in itself harm the Copicat.
Neither will the 250V from the secondary.
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17th Dec 2014, 10:27 pm | #89 |
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Re: WEM Copicat Custom
I suggest this as a way forward.
Disconnect the red HT wires from the circuit and preferably insulate them. If the transformer than stays cool it may have survived. If not I'm afraid you'll need a new one. Measure the resistance between each of the red HT wires and each pin of the mains plug. SET TURNED ON< BUT NOT CONNECTED TO THE MAINS. Should read open circuit. If not transformer has had it. Measure the AC voltage between the red wires, It may be more than 250V because the transformer is unloaded. Snip out C9 and measure the resistance across the smoothers. You should initially see a short circuit as current rushes into the smoothers. The reading should then rise towards infinity as the caps charge. If all theses tests are OK you can remake the connections and apply power, after which you can check the DC voltages across the smoothers.
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17th Dec 2014, 11:06 pm | #90 |
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Re: WEM Copicat Custom
Ok, thanks, will give this a try tomorrow. I noticed elsewhere on this forum that someone was talking about the selenium rectifier being unreliable and that it's better to replace them with a 4007 diode and a small 1W resistor (390 ohm I think they said). Just wondered if that's another possible problem. I'll have another really good look over the board too for any kind of short. The caps and resistors on the valve side of the board are pretty tightly squashed together with some resistors hidden under the caps etc. I noticed from photos of other Mk IIIs online that some have these components on both sides, perhaps to make more space, or were put on the other side when repaired.
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17th Dec 2014, 11:39 pm | #91 |
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Re: WEM Copicat Custom
Having been subjected to around 300V I strongly suspect that the record head will have been damaged and will require replacing.
I am not too familiar with the typical resistance of a tape head but would guestimate that the winding resistance should be between 500 and 2000 ohms. Since these heads are now quite expensive items you need to factor the price into the viability of repairing this machine. Al
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18th Dec 2014, 9:03 am | #92 | |
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Re: WEM Copicat Custom
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You can test it using the diode function on your meter as described in the first post in this thread:- https://www.vintage-radio.net/forum/...ad.php?t=42194 Everything seems to have been going well with your fault finding until you attempted to measure the HT voltage, drew a spark and later got a reading of 790. I can only guess that one of your croc clips sorted out one of the smoothing capacitors, so hence the spark. I can't explain the melting of C9 unless it was indeed subjected to 790 Volts. The zero volt reading on pin 2 of V2 would be consistent with C9 being short-circuit.
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18th Dec 2014, 10:31 am | #93 |
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Re: WEM Copicat Custom
For C9 to have failed again there must be a fault in the bias oscillator resulting in incorrect output amplitude/frequency. The bias oscillator is regulated by rectification on the grid (-18V) which is then used for the voltage follower output transistor.
I suggest you do a bit more work before powering on again: - Replace C8, C9 again and C10. C8 will be a high tolerance mica type and all three need to be high voltage (630V minimum). - Check values of resistors R16 (47K) and R30 (82K) - Change the mains transformer tapping to 240V. - Lower the HT with a resistor in series with the rectifier which will also give a little short circuit protection for the transformer. I would try 1K ohms 5W type. - Check the resistance of the recording head. - Check you are using the right valve type (as this will affect bias conditions). |
18th Dec 2014, 11:15 am | #94 |
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Re: WEM Copicat Custom
Another extract from the circuit.
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18th Dec 2014, 12:00 pm | #95 |
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Re: WEM Copicat Custom
In post 44 you mention a 6BR8 in the middle valve position. In your copicat this would be incorrect. Looking at the pcb photo, yours should have three ECC83s. There is a model with the 6BR8, but these were, in my experience, usually the earlier models with the tagboard layout. The 6BR8 is the one used for the bias oscillator and is nearest the oscillator coil.
I have only glanced through all the posts made so far, so please excuse me if this has already been pointed out! Check out this site for superb detailed info. http://www.backfromthesixties.co.uk/...s_copicat_mkii Circuit diagram for the 6BR8 model from there attached.
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18th Dec 2014, 12:12 pm | #96 |
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Re: WEM Copicat Custom
That explains what looked like strange voltages on V2 in post #44.
I've edited the electrode designations in that post. I'm thinking about what implications this has for the fault finding and test results so far.
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18th Dec 2014, 12:28 pm | #97 |
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Re: WEM Copicat Custom
Looks like we need a circuit for the version with three ECC83's then?
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18th Dec 2014, 12:29 pm | #98 |
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Re: WEM Copicat Custom
Graham,
I was thinking the same...
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18th Dec 2014, 12:40 pm | #99 |
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Re: WEM Copicat Custom
Graham,
The circuit designations appear to be different on most of the circuits available. Here's my own hand drawn circuit taken directly from a working model. Does this help? The forum image size restrictions make clarity 'iffy'! I can mail the original image (about 2Mb) if required. EDIT: I have one coming in for repair later today. Don't know which version it is, 6BR8 or ECC83. If it's the right one, I can probably help with photos and voltage measurements etc.
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18th Dec 2014, 12:51 pm | #100 |
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Re: WEM Copicat Custom
The 200 pF capacitor (C9) which was replaced would go the anode ie pin 1 of an ECC83, or pin 2 of a 6BR8.
So did the OP replace the correct capacitor with the correct value on the correct pin?
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