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Old 12th Jan 2015, 6:50 am   #141
evilmoisture
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Default Re: WEM Copicat Custom

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Originally Posted by PJL View Post
Did you change it to the 240V mains tap on the transformer?
Do I need to? I'm in France, the mains voltage is 220 here.

Will build a lamp limiter and do the tests you suggest, thanks!
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Old 12th Jan 2015, 11:13 am   #142
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Default Re: WEM Copicat Custom

Correction, it is already on 240v, red and black wires
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Old 12th Jan 2015, 1:04 pm   #143
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Default Re: WEM Copicat Custom

France is supposed to be 230V but the intention of using the 240V tap is to try to bring down the HT voltage a bit. Once the unit is working properly you can measure the LT voltage to identify the best tap for your local mains.
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Old 18th Jan 2015, 3:03 pm   #144
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Default Re: WEM Copicat Custom

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Did you change it to the 240V mains tap on the transformer?
1. Use a lamp limiter.
2. Clip your meter (1000V range) across C14 (junction of R27/R28 and chassis).
3. Turn on and keep an eye on the voltage. If it does not rise quickly to 300V and the lamp is bright then switch off and report back here. It should initially rise to 350V or so then fall away as the valves warm up. If it falls below 250V switch off and report back here.
4. Turn off and clip your meter (200V range) across R28 (2.2K)
5. Turn on and monitor the voltage. If it exceeds 50V then switch off and report back here.

Hi, finally made a lamp limiter. The results of the tests above are as follows:
First test (measuring voltage across C14), lamp remained dim / off and the voltage rose to about 370v and stayed there.
Second test of R28, the voltage rose to around 8v and then down to around 1v
Looks good?
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Old 18th Jan 2015, 4:35 pm   #145
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Took the plunge and tested it, still no sound from any of the heads (tried touching them with the tip of a screwdriver). When I turn the gain pots the hum gets louder, as if there is some amplification going on. Also when I move the swell and reverb pots the hum changes slightly. Tried swapping 2 of the valves for 2 spare ones and no change. Tried in both positions of the "footswitch" (or whats left of it, just the bare wires twisted or untwisted at the end of the lead), in one position the hum is louder. I assume this is 'normal' background mains hum.
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Old 18th Jan 2015, 6:31 pm   #146
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Default Re: WEM Copicat Custom

I've had to re-read this lengthy thread to familiarise myself with what the initial problem was.

It boiled down to R28 (2.2K Red, Red, Red) burning out due to it carrying excessive current, this being caused by C9 going short-circuit twice. Later one of the smoothers also went short-circuit and was replaced.

The situation now is that you have a respectable HT voltage 370V, but only one volt across R28. This points to less than half a milliamp flowing through R28, which is rather low and may account for the elevated HT voltage.

I think the thing to do now is to take voltage readings on all the valves so that we can get an idea as to where the problem is.
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Old 18th Jan 2015, 7:09 pm   #147
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Default Re: WEM Copicat Custom

As per post 44 I took readings again as follows:
(didnt read the heaters)
V1
1: 3v
2: 0.5v
3: 0v
4/5 heater
6: 3v
7: 0v
8 0v
9 (heater)

V2
1: 3v
2: 0v
3: 0v
4/5 (heaters)
6: 3v
7: 0v
8: 0v
9 (heater)

V3
1: 3v
2: 0v
3: 0v
4/5 (heaters)
6: 3v
7: 1.6v
8: 0v
9: (heater)

C9 looks a little black (again) but it's not short circuit
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Old 18th Jan 2015, 7:20 pm   #148
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Default Re: WEM Copicat Custom

At first glance (assuming the readings are correct) it's obvious that you have no HT!

Is HT present across all three of the smoothing capacitors?

Is R28 coded red, red, red and measuring 2.2kohms (2200 ohms)?
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Old 18th Jan 2015, 7:47 pm   #149
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I tested between the - of the 3 smoothing caps (where one of the red wires from the transformer is) and the other end of each cap and I get no voltage. I measured the resistance of both resistors R27 and R28 and I get the correct values, 4.7k and 2.2k. Yes the color code is red red red on the (new) R28.
I also measured between both red transformer wires and I get 350v. Double checked that I wired up the smoother caps correctly and it looks right.
The rectifier has also died?
Here's a photo anyway. It's not completeley clear but the thin red wire goes from one end of the rectifier (diode) to the end of R28 and smoother, top right
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Old 18th Jan 2015, 7:55 pm   #150
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Default Re: WEM Copicat Custom

I'll study your picture and see what I can make of it.

In the mean time can you test the rectifier (diode) as described in post #92.
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Old 18th Jan 2015, 8:02 pm   #151
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Default Re: WEM Copicat Custom

Thanks!
My meter has a diode testing setting. Just tested it and one way round it is open circuit, the other way it says 655.
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Old 18th Jan 2015, 8:11 pm   #152
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Default Re: WEM Copicat Custom

If that's point 655 (.655) the diode's OK.
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Old 18th Jan 2015, 8:24 pm   #153
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Default Re: WEM Copicat Custom

Just says 655 but that might be my meter

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Old 18th Jan 2015, 8:36 pm   #154
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Default Re: WEM Copicat Custom

I've studied your picture and compared it with the one in post #7.

One sleeved red wire from the HT winding goes to the diode.

The other sleeved red wire from the HT winding appears to go to the negative side of all three smoothing caps.

There should be another wire going from common negative to the negative supply rail. Is this wire present? You may remember that you ran a second wire from the common negative connection to the sub-chassis, but subsequently removed it.
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Old 18th Jan 2015, 8:40 pm   #155
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Default Re: WEM Copicat Custom

Oh ok that must be it. I did indeed remove one that was coming from negative (on the smoothers) to the subchassis (switch assembly), because there is another connection doing that already. Should I put it back? Or take a wire from the chassis to the negative smoother wire?

Same thing in either case I guess?

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Old 18th Jan 2015, 8:52 pm   #156
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because there is another connection doing that already. Should I put it back? Or take a wire from the chassis to the negative smoother wire?
If the connection I've bolded is still present, then no additional wire is needed.

I've checked the rest of the wiring and it looks OK, if a little untidy.

Regardless of whether the wire under discussion is present, you should get a reading of about 300VAC between the two sleeved red wires and a high DC voltage across each of the three smoothers. If the AC voltage is present, but the DC voltage isn't, then this points to an open circuit diode. I doubt this though as the diode looks OK, testing open circuit in one direction and having a forward volt drop of about 0.655 volts.
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Old 18th Jan 2015, 8:52 pm   #157
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Default Re: WEM Copicat Custom

Bearing in mind that I also changed the mains cable to a 3 wire one with earth, and the chassis is now earthed, so if I add this wire the common negative will be going to earth too, just checking this is correct.
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Old 18th Jan 2015, 8:54 pm   #158
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Default Re: WEM Copicat Custom

If I test between chassis and the common negative / smoothers there is no connection
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Old 18th Jan 2015, 9:01 pm   #159
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Ok, tested again, I do indeed get 270 AC across the 2 red wires from the transformer, and 370 DC on each smoother cap.
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Old 18th Jan 2015, 9:01 pm   #160
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Default Re: WEM Copicat Custom

Quote:
Originally Posted by evilmoisture
If I test between chassis and the common negative / smoothers there is no connection.
Well there should be a connection.

If you look at the circuit in post #112 you'll see that each of the smoothers has an arrow (denoting a chassis connection) pointing downwards. The negative supply rail has a similar arrow.
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