VCM 163 No.1. Problem while calibrating - Page 5 - UK Vintage Radio Repair and Restoration Discussion Forum

Dekatron · 16th Nov 2021, 3:24 pm

What happens if you hook the wires from the working 163 to the non-working amplifier inputs, the other way around - does the meter reach the Cal.-position then when driven from the working 163?

What happens if you hook up the outputs to the meter from the non-working amplifier to the meter in the working 163, what does it show then?

What I am looking for is to try to see if the amplifier, the wiring or the meter is to blame for the fault you experience.

If you make a matrix with the amplifier, oscillator and the wiring you should be able to see what combinations that work and not work and by that discern what part isn't working correctly.

HBWOODY · 16th Nov 2021, 8:28 pm

I understand what you are saying.
When I hook up the wires from the working 163 to the non working amplifier inputs the meter does not move.
I will do what you suggested with the meter tomorrow.
I have recently tested the meter resistance and its FSD as it is a replacement of the original meter.

HBWOODY · 17th Nov 2021, 10:47 am

When I hook up the outputs to the meter from the non-working amplifier to the meter in the working 163 the needle does not move to the Calibration point.
When I hook up the outputs to the meter from the working amplifier to the meter in the non working 163 the needle moves to the Calibration point.

Dekatron · 17th Nov 2021, 12:27 pm

Where did you connect the wires, directly on the circuit board or with the lugs at the meter?

If at the circuit board you need to check the soldering and the traces and measure the semiconductors as well as the components.

If you used the lugs at the meter you will need to check all above as well as the wiring between the amplifier and the meter too.

You could of course also use an isolated scope, so you don't get ground loops, and check the signal on the amplifier to see if/where it disappears.

HBWOODY · 17th Nov 2021, 3:42 pm

I connected the wires directly from the circuit board to the terminals on the meters.
At the moment I am checking the components and the continuity on the circuit board.
I do have Mini DSO (DS211) scope but have not cleared how to use it.

HBWOODY · 18th Nov 2021, 8:32 pm

Well it was a long journey and a successful one. Found the culprit which was one of the diodes on tags 4 and 5 of the amplifier board. I again have learnt so much and the 163 has become much more familiar to me which has enabled me to understand the circuit and see where problems may occur.
Thank you all for your input especially Martin who has persevered with my ignorance where many would have understandably given up.
Will now calibrate the 163 and put it to work testing some valves.
Till the next time.
Good health to you all.
Haydn

Dekatron · 18th Nov 2021, 8:46 pm

I'm glad you found the culprit and that it was possible to fix it easily!

I've heard about a similar case but it didn't result in exactly the same fault so it is good to know about one more type of error and how it manifests itself.

It's also good to know that the amplifier works in itself.

Wetubes · 27th Mar 2022, 12:38 pm

Dekatron - Martin, I understand your are the expert in repairing AVO VCM 163. I have both mA and mA/V analog meters working but not smooth. Do you or you know anyone can service these meters?

Thanks

Station X · 27th Mar 2022, 1:00 pm

Hello and welcome to the forums.

Please see this thread concerning Dekatron - Martin:-

https://www.vintage-radio.net/forum/...d.php?t=189725

Personally I know of no company which services moving coil meters.

Wetubes · 27th Mar 2022, 1:56 pm

Graham

Thanks for your welcome message and update re Martin.

Martin

I am a new member and like to wish you a speedy recovery.

16th Nov 2021, 3:24 pm	#81
Dekatron Octode Join Date: May 2009 Location: Linkoping, Sweden Posts: 1,465	Re: VCM 163 No.1. Problem while calibrating What happens if you hook the wires from the working 163 to the non-working amplifier inputs, the other way around - does the meter reach the Cal.-position then when driven from the working 163? What happens if you hook up the outputs to the meter from the non-working amplifier to the meter in the working 163, what does it show then? What I am looking for is to try to see if the amplifier, the wiring or the meter is to blame for the fault you experience. If you make a matrix with the amplifier, oscillator and the wiring you should be able to see what combinations that work and not work and by that discern what part isn't working correctly. __________________ Martin, Sweden

16th Nov 2021, 8:28 pm	#82
HBWOODY Pentode Join Date: Mar 2020 Location: Bodmin, Cornwall, UK. Posts: 212	Re: VCM 163 No.1. Problem while calibrating I understand what you are saying. When I hook up the wires from the working 163 to the non working amplifier inputs the meter does not move. I will do what you suggested with the meter tomorrow. I have recently tested the meter resistance and its FSD as it is a replacement of the original meter.

17th Nov 2021, 10:47 am	#83
HBWOODY Pentode Join Date: Mar 2020 Location: Bodmin, Cornwall, UK. Posts: 212	Re: VCM 163 No.1. Problem while calibrating When I hook up the outputs to the meter from the non-working amplifier to the meter in the working 163 the needle does not move to the Calibration point. When I hook up the outputs to the meter from the working amplifier to the meter in the non working 163 the needle moves to the Calibration point.

17th Nov 2021, 12:27 pm	#84
Dekatron Octode Join Date: May 2009 Location: Linkoping, Sweden Posts: 1,465	Re: VCM 163 No.1. Problem while calibrating Where did you connect the wires, directly on the circuit board or with the lugs at the meter? If at the circuit board you need to check the soldering and the traces and measure the semiconductors as well as the components. If you used the lugs at the meter you will need to check all above as well as the wiring between the amplifier and the meter too. You could of course also use an isolated scope, so you don't get ground loops, and check the signal on the amplifier to see if/where it disappears. __________________ Martin, Sweden

17th Nov 2021, 3:42 pm	#85
HBWOODY Pentode Join Date: Mar 2020 Location: Bodmin, Cornwall, UK. Posts: 212	Re: VCM 163 No.1. Problem while calibrating I connected the wires directly from the circuit board to the terminals on the meters. At the moment I am checking the components and the continuity on the circuit board. I do have Mini DSO (DS211) scope but have not cleared how to use it.

18th Nov 2021, 8:32 pm	#86
HBWOODY Pentode Join Date: Mar 2020 Location: Bodmin, Cornwall, UK. Posts: 212	Re: VCM 163 No.1. Problem while calibrating Well it was a long journey and a successful one. Found the culprit which was one of the diodes on tags 4 and 5 of the amplifier board. I again have learnt so much and the 163 has become much more familiar to me which has enabled me to understand the circuit and see where problems may occur. Thank you all for your input especially Martin who has persevered with my ignorance where many would have understandably given up. Will now calibrate the 163 and put it to work testing some valves. Till the next time. Good health to you all. Haydn

18th Nov 2021, 8:46 pm	#87
Dekatron Octode Join Date: May 2009 Location: Linkoping, Sweden Posts: 1,465	Re: VCM 163 No.1. Problem while calibrating I'm glad you found the culprit and that it was possible to fix it easily! I've heard about a similar case but it didn't result in exactly the same fault so it is good to know about one more type of error and how it manifests itself. It's also good to know that the amplifier works in itself. __________________ Martin, Sweden

27th Mar 2022, 12:38 pm	#88
Wetubes Diode Join Date: Mar 2022 Location: Hong Kong Posts: 3	Re: VCM 163 No.1. Problem while calibrating Dekatron - Martin, I understand your are the expert in repairing AVO VCM 163. I have both mA and mA/V analog meters working but not smooth. Do you or you know anyone can service these meters? Thanks

27th Mar 2022, 1:00 pm	#89
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: VCM 163 No.1. Problem while calibrating Hello and welcome to the forums. Please see this thread concerning Dekatron - Martin:- https://www.vintage-radio.net/forum/...d.php?t=189725 Personally I know of no company which services moving coil meters. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

27th Mar 2022, 1:56 pm	#90
Wetubes Diode Join Date: Mar 2022 Location: Hong Kong Posts: 3	Re: VCM 163 No.1. Problem while calibrating Graham Thanks for your welcome message and update re Martin. Martin I am a new member and like to wish you a speedy recovery.