WEM Copicat Custom - Page 3 - UK Vintage Radio Repair and Restoration Discussion Forum

Station X · 17th Dec 2014, 3:37 pm

I think the next thing for you to do is to take DC voltage readings from each valve pin to chassis (with the unit switched on of course) and post the readings here for analysis.

No need to do the heater pins, assuming of course that all the valves are lighting up.

You could also measure all resistors (with power off of course) expect some strange readings though as some resistors are shunted by others.

Welsh Anorak · 17th Dec 2014, 3:42 pm

Hi
Just fixed one of these with no replay output and the fault was due to a small Hunts capacitor (of course!) hidden by the larger electrolytics and also the coupling capacitor to the swell control being open.
Glyn

evilmoisture · 17th Dec 2014, 4:04 pm

@Station X ok will do and get back to you with the readings.
@Welsh Anorak congrats on getting yours working, not sure which caps you mean though, could you point them out on here? The one I replaced was a small cap almost behind the largest one, C9, possibly the same one? http://www.vintagehofner.co.uk/brita...opicatmk3.html

evilmoisture · 17th Dec 2014, 4:52 pm

Here are the readings for the 3 valves, as numbered in the attached photo, which I think is the same pinouts as on the datasheet.

A: ECC83
1 =46v ANODE
2 = 0v GRID
3 = 0.34v CATHODE
(4,5 = heater)
6 = going between plus and minus 0.1v ANODE
7 = 0v GRID
8 = 0.33v CATHODE
(9 = heater)

B: ECC83
1 = 57v ANODE
2 = 0v GRID
3 = 0v CATHODE
(4,5 = heater)
6 = 48.5v ANODE
7 = 0v GRID
8 = 0.6v CATHODE
(9 = heater).

C: ECC83
1 = 77.5v ANODE
2 = -4.1v GRID
3 = 0v CATHODE
(4,5 = heater)
6 = 47.2v ANODE
7 = -0.2v GRID
8 = 0.41v CATHODE
(9 = heater)

I haven't measured all the resistors yet, but R1 and R2 (input resistors) are zero ohms, not sure this is right...

Station X · 17th Dec 2014, 5:10 pm

R1 and R2 measure zero because they are short-circuited by the contacts of the input jacks. You'll need to insert an otherwise disconnected plug into the jack to get a true reading.

Station X · 17th Dec 2014, 5:15 pm

Can you check the HT voltages by measuring the DC Volts across C13 and C14 please.

evilmoisture · 17th Dec 2014, 5:32 pm

Got a huge spark when i tried! Is it better to crocodile clip the meter probes to the caps and then plug it in? My cheap meter says 500v max, 10A, hope it wont blow...

Oh yes sorry, ok R1 and R2 are around 1 meg. R3 R4 and R5 are as they should be. R6 is 270k, R7 is 410 k...thats as far as I got

Station X · 17th Dec 2014, 5:37 pm

On a preliminary glance, you readings are well below those expected. Measuring the HT voltages may throw some light on this.

The valve you call 'A' is V1. Pins 1 and 6 should have similar voltages. Suspect a bad contact between the valve pins and the holder, or open circuit R5.

Techman · 17th Dec 2014, 5:39 pm

You are starting to frighten me!

I think you need to learn how to use your multimeter properly before you go any further!

DON'T use the 10 amp range - or ANY other amp ranges to make voltage checks!

High voltage ranges ONLY - and work down to lower ranges if needed.

Station X · 17th Dec 2014, 5:42 pm

There is no way you should get a huge spark with a meter on a VOLTS range. That is so long as you don't short-circuit something with your probe. Standard practice is to croc clip the negative lead to chassis (also the negative side of the smoothers) and probe any points to be measured with the positive lead.

Techman · 17th Dec 2014, 5:42 pm

Use 500 volt range and croc clip black negative lead to chassis and take voltage readings with the red probe lead - taking great care not to let it slip!

Edit: post crossed with Graham again.

Station X · 17th Dec 2014, 5:51 pm

Another strange thing is that V2, which I assume is the valve you call 'B', should have the full HT voltage on pin 2. We know it was there because it was being short-circuited by C9 which you replaced. Now it seems to have gone!

evilmoisture · 17th Dec 2014, 5:52 pm

Oops yes, ok got it, sorry!
Across both caps (from either side of R27 and the negative wire from the transformer) its the same, about 790v

evilmoisture · 17th Dec 2014, 6:06 pm

Ok I just swapped V1 for another one and now I'm getting 50v on pin 1 and 31v on pin 6.
Nothing at all on V2 pin 2

Techman · 17th Dec 2014, 6:07 pm

You can't have 790 volts, that's far too high!

I'm wondering whether you've 'popped' your meter with that spark on the wrong range.

Station X · 17th Dec 2014, 6:07 pm

Quote:

it's the same, about 790v

Er....... I don't think so! Either you meter is faulty, you're using the wrong sockets on it or you have it set to the wrong range.

Can you post a picture of what you're doing please.

Why does your picture show four croc clips?

Station X · 17th Dec 2014, 6:09 pm

I'll leave this to Techman for the moment if he doesn't mind. I have another job to do here.

Techman · 17th Dec 2014, 6:09 pm

You need to check your meter is reading correctly on a 'known' voltage before you go any further - a 9 volt battery will do to start with.

Techman · 17th Dec 2014, 6:11 pm

Yes, sorry Graham, I seem to keep crossing posts with you.

Techman · 17th Dec 2014, 6:17 pm

Let us know when you've checked your meter.

You should expect HT voltage readings over 200 volts at the smoothing capacitors, but below 300 volts.

17th Dec 2014, 3:37 pm	#41
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: WEM Copicat Custom I think the next thing for you to do is to take DC voltage readings from each valve pin to chassis (with the unit switched on of course) and post the readings here for analysis. No need to do the heater pins, assuming of course that all the valves are lighting up. You could also measure all resistors (with power off of course) expect some strange readings though as some resistors are shunted by others. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

17th Dec 2014, 3:42 pm	#42
Welsh Anorak Dekatron Join Date: Apr 2005 Location: North Wales, UK. Posts: 6,918	Re: WEM Copicat Custom Hi Just fixed one of these with no replay output and the fault was due to a small Hunts capacitor (of course!) hidden by the larger electrolytics and also the coupling capacitor to the swell control being open. Glyn

17th Dec 2014, 4:04 pm	#43
evilmoisture Retired Dormant Member Join Date: Dec 2014 Location: Ile-de-france, Paris, France. Posts: 84	Re: WEM Copicat Custom @Station X ok will do and get back to you with the readings. @Welsh Anorak congrats on getting yours working, not sure which caps you mean though, could you point them out on here? The one I replaced was a small cap almost behind the largest one, C9, possibly the same one? http://www.vintagehofner.co.uk/brita...opicatmk3.html

17th Dec 2014, 4:52 pm	#44
evilmoisture Retired Dormant Member Join Date: Dec 2014 Location: Ile-de-france, Paris, France. Posts: 84	Re: WEM Copicat Custom Here are the readings for the 3 valves, as numbered in the attached photo, which I think is the same pinouts as on the datasheet. A: ECC83 1 =46v ANODE 2 = 0v GRID 3 = 0.34v CATHODE (4,5 = heater) 6 = going between plus and minus 0.1v ANODE 7 = 0v GRID 8 = 0.33v CATHODE (9 = heater) B: ECC83 1 = 57v ANODE 2 = 0v GRID 3 = 0v CATHODE (4,5 = heater) 6 = 48.5v ANODE 7 = 0v GRID 8 = 0.6v CATHODE (9 = heater). C: ECC83 1 = 77.5v ANODE 2 = -4.1v GRID 3 = 0v CATHODE (4,5 = heater) 6 = 47.2v ANODE 7 = -0.2v GRID 8 = 0.41v CATHODE (9 = heater) I haven't measured all the resistors yet, but R1 and R2 (input resistors) are zero ohms, not sure this is right... Attached Thumbnails

17th Dec 2014, 5:10 pm	#45
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: WEM Copicat Custom R1 and R2 measure zero because they are short-circuited by the contacts of the input jacks. You'll need to insert an otherwise disconnected plug into the jack to get a true reading. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

17th Dec 2014, 5:15 pm	#46
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: WEM Copicat Custom Can you check the HT voltages by measuring the DC Volts across C13 and C14 please. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

17th Dec 2014, 5:32 pm	#47
evilmoisture Retired Dormant Member Join Date: Dec 2014 Location: Ile-de-france, Paris, France. Posts: 84	Re: WEM Copicat Custom Got a huge spark when i tried! Is it better to crocodile clip the meter probes to the caps and then plug it in? My cheap meter says 500v max, 10A, hope it wont blow... Oh yes sorry, ok R1 and R2 are around 1 meg. R3 R4 and R5 are as they should be. R6 is 270k, R7 is 410 k...thats as far as I got

17th Dec 2014, 5:37 pm	#48
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: WEM Copicat Custom On a preliminary glance, you readings are well below those expected. Measuring the HT voltages may throw some light on this. The valve you call 'A' is V1. Pins 1 and 6 should have similar voltages. Suspect a bad contact between the valve pins and the holder, or open circuit R5. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

17th Dec 2014, 5:39 pm	#49
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: WEM Copicat Custom You are starting to frighten me! I think you need to learn how to use your multimeter properly before you go any further! DON'T use the 10 amp range - or ANY other amp ranges to make voltage checks! High voltage ranges ONLY - and work down to lower ranges if needed.

17th Dec 2014, 5:42 pm	#50
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: WEM Copicat Custom There is no way you should get a huge spark with a meter on a VOLTS range. That is so long as you don't short-circuit something with your probe. Standard practice is to croc clip the negative lead to chassis (also the negative side of the smoothers) and probe any points to be measured with the positive lead. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

17th Dec 2014, 5:42 pm	#51
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: WEM Copicat Custom Use 500 volt range and croc clip black negative lead to chassis and take voltage readings with the red probe lead - taking great care not to let it slip! Edit: post crossed with Graham again.

17th Dec 2014, 5:51 pm	#52
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: WEM Copicat Custom Another strange thing is that V2, which I assume is the valve you call 'B', should have the full HT voltage on pin 2. We know it was there because it was being short-circuited by C9 which you replaced. Now it seems to have gone! __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

17th Dec 2014, 5:52 pm	#53
evilmoisture Retired Dormant Member Join Date: Dec 2014 Location: Ile-de-france, Paris, France. Posts: 84	Re: WEM Copicat Custom Oops yes, ok got it, sorry! Across both caps (from either side of R27 and the negative wire from the transformer) its the same, about 790v

17th Dec 2014, 6:06 pm	#54
evilmoisture Retired Dormant Member Join Date: Dec 2014 Location: Ile-de-france, Paris, France. Posts: 84	Re: WEM Copicat Custom Ok I just swapped V1 for another one and now I'm getting 50v on pin 1 and 31v on pin 6. Nothing at all on V2 pin 2

17th Dec 2014, 6:07 pm	#55
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: WEM Copicat Custom You can't have 790 volts, that's far too high! I'm wondering whether you've 'popped' your meter with that spark on the wrong range.

17th Dec 2014, 6:09 pm	#57
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: WEM Copicat Custom I'll leave this to Techman for the moment if he doesn't mind. I have another job to do here. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

17th Dec 2014, 6:09 pm	#58
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: WEM Copicat Custom You need to check your meter is reading correctly on a 'known' voltage before you go any further - a 9 volt battery will do to start with.

17th Dec 2014, 6:11 pm	#59
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: WEM Copicat Custom Yes, sorry Graham, I seem to keep crossing posts with you.

17th Dec 2014, 6:17 pm	#60
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: WEM Copicat Custom Let us know when you've checked your meter. You should expect HT voltage readings over 200 volts at the smoothing capacitors, but below 300 volts.