EKCO U122 - Faulty on/off switch - UK Vintage Radio Repair and Restoration Discussion Forum

DonaldStott · 18th Jan 2021, 2:09 pm

I'm currently pulling apart an Ekco U122 and there are several bodges that I will include in a more general Thread on this set.

One of the immediate problems is a faulty on/off switch that has continuity across the LIVE and NEUTRAL tags when the switch is either on or off!

I can easily replace this with a modern 470k pot but just out of interest I thought that I would disassemble the switch, firstly to see if I could identify the problem and secondly, for my own illumination, to see if I could understand how it works!

Here are some images of the disassembled parts and a close up of the switch - needless to say I've failed on both counts. I can't see what the problem is and I'm not sure how it works?

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Can anyone enlighten me and advise if this switch is fixable?

Station X · 18th Jan 2021, 2:11 pm

I have repaired similar switches.

https://www.vintage-radio.net/forum/...0&postcount=36

The first question is does what I call the yoke (the bit with the triangular cut out) flip position when you operate the switch via the knob? Given that the switch has continuity in either position I'd say no, it isn't moving. There'll be a pin which engages in the 'V' shape or a similar arrangement to toggle the yoke.

EDIT. Looks like one of the brass contacts may be bent?

DonaldStott · 18th Jan 2021, 4:56 pm

Thanks Graham - the link to your own earlier Post proved very enlightening and educational.

My spring loaded pin was moving but the Paxolin 'yoke' wouldn't budge which meant that the two brass contacts were somehow stuck in place. Very gently eased them both up and the yoke now rotates with the spring loaded pin. Checked the external tabs with my DMM and everything is as it should be.

Two images, switch on followed by switch off:-

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Two further questions:-

1. I'd like to 'freshen up' the faces of the contacts and I've considered using a small strip of very fine wet&dry - will that be problematic in any way?

2 I need to reattach the disassembled switch parts using small bolts but need to ensure there is no snagging with the potentiometer slider - what size is recommended?

I'll also follow Graham's advice and apply a small dab of silicone grease where shown - thanks again.

Station X · 18th Jan 2021, 5:46 pm

I doubt the contacts will need cleaning but if you must use fine glass paper rather than emery paper/cloth. A squirt of Servisol wouldn't go amiss.

I don't know about the size of bolts as the pot I repaired used bent over tabs rather than rivets. Same diameter of the rivets I guess. Aren't they insulated by holes in the hard plastic casing.

I expect someone will be along to say that silicone grease shouldn't be allowed near electrical contacts as it creeps. All I can say is that I've never had any problems with it.

ms660 · 18th Jan 2021, 6:04 pm

I've never had problems with silicone grease either, a tube of it was standard issue for lots of us TV service techs back in the day.

Lawrence.

DonaldStott · 19th Jan 2021, 1:25 pm

What I did was to use a 6BA tap to thread the hard plastic casing and inserted 6BA bolts from the tag side. I needed to ensure that the new bolts didn't snag the potentiometer slider so I've used my Dremel to cut them off flush with the inside face. The switch mechanism was secured first with masking tape to ensure that metal filings didn't fall inside. I'm thinking about a small dab of epoxy inside to secure the bolts?

So far, so good ...

And then we find that the potentiometer is playing up - I'm getting intermittent and inconsistent readings on my DMM as I rotate the shaft. I expect 0 - 500ohms or thereabouts but I'm getting nothing (reading 1 on my DMM) along most of the track and then the occasional 50-60 ohms! Tried cleaning the track carefully with Deoxit Fader F5 (good for things that slide rather than rotate) but this has made little or no difference. Can't see any problems with the track when examined closely with my loupe so not sure where this new problem lies?

Station X · 19th Jan 2021, 1:29 pm

Bend the wiper so that it presses harder against the track?

Test the track using one meter probe as a wiper. It's not unknown for the track to wear away. Often the wiper will have two or three points (inverted dimples) of contact with the track.

ms660 · 19th Jan 2021, 1:29 pm

Quote:

Originally Posted by DonaldStott

And then we find that the potentiometer is playing up - I'm getting intermittent and inconsistent readings on my DMM as I rotate the shaft. I expect 0 - 500ohms or thereabouts but I'm getting nothing (reading 1 on my DMM) along most of the track and then the occasional 50-60 ohms!

500k in the schematic I'm looking at.

Lawrence.

Station X · 19th Jan 2021, 1:33 pm

Ah yes. If the range used is too low ''1' can be displayed as an over range indication.

DonaldStott · 19th Jan 2021, 3:03 pm

Thanks Graham and Lawrence - the whole pot is a bit mucky, as is the rest of this set, so I'll give it a good clean with IPA and look at the track and wiper contacts again.

I appreciate that it's a 500k pot so my DMM was on the 2M range but getting those strange readings!

I'll report back later...

DonaldStott · 19th Jan 2021, 4:38 pm

Ok 500k pot thoroughly cleaned with IPA - the track was really mucky indeed!

Although I'm getting continuous readings with my DMM when I rotate the control I am, however, now reading 0-902k, almost twice what it should be?

Looking at the circuit diagram (Trader Sheet 995) is it possible to adjust the value of any of the resistors associated with the volume control R9?

Station X · 19th Jan 2021, 6:57 pm

Any markings on it? It could have been 1M to start with.

DonaldStott · 19th Jan 2021, 8:42 pm

I've scoured all parts of this switch/pot with my loupe but can't find anything that indicates a value?

It may have had a label on the side, evidence of residual glue, but this is long gone - some numbers are barely visible:-

34673/2

And on the base it has:-

EGEN
MADE IN ENGLAND
250V 1A

That's all folks ... hope this helps?

Station X · 20th Jan 2021, 10:00 am

What value of resistance do you read between the two outer tags 0f the potentiometer?

DonaldStott · 20th Jan 2021, 12:57 pm

Quote:

Originally Posted by Station X

What value of resistance do you read between the two outer tags 0f the potentiometer?

As expected that's around 895k - seems to have lost a few k overnight!

Station X · 20th Jan 2021, 2:13 pm

I'd be inclined to try it in the set and see what happens.

DonaldStott · 20th Jan 2021, 2:25 pm

Quote:

Originally Posted by Station X

I'd be inclined to try it in the set and see what happens.

Thanks, will do but trying it in the set is several weeks away yet while I contemplate the scale of work that needs to be done on this Ekco U122.

I'll start another general Thread to illustrate the challenges I have e.g almost every wire I touch crumbles and will need replacing! Also, V5 (UY41) has been replaced with something I've never seen before!

In the interests on continuity

I will link back to this Thread.

Herald1360 · 20th Jan 2021, 5:01 pm

Quote:

Originally Posted by DonaldStott

Also, V5 (UY41) has been replaced with something I've never seen before!

Tease!

What would that be then- piccy?

DonaldStott · 21st Jan 2021, 8:16 pm

Quote:

Originally Posted by Herald1360

What would that be then- piccy?

Coming soon ...

DonaldStott · 30th Jan 2021, 6:55 pm

Quote:

Originally Posted by ms660

I've never had problems with silicone grease either, a tube of it was standard issue for lots of us TV service techs back in the day.

What about lithium grease?

18th Jan 2021, 2:09 pm	#1
DonaldStott Octode Join Date: Aug 2015 Location: Glasgow, UK. Posts: 1,842	EKCO U122 - Faulty on/off switch I'm currently pulling apart an Ekco U122 and there are several bodges that I will include in a more general Thread on this set. One of the immediate problems is a faulty on/off switch that has continuity across the LIVE and NEUTRAL tags when the switch is either on or off! I can easily replace this with a modern 470k pot but just out of interest I thought that I would disassemble the switch, firstly to see if I could identify the problem and secondly, for my own illumination, to see if I could understand how it works! Here are some images of the disassembled parts and a close up of the switch - needless to say I've failed on both counts. I can't see what the problem is and I'm not sure how it works? . Can anyone enlighten me and advise if this switch is fixable? __________________ BVWS Member

18th Jan 2021, 2:11 pm	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: EKCO U122 - Faulty on/off switch I have repaired similar switches. https://www.vintage-radio.net/forum/...0&postcount=36 The first question is does what I call the yoke (the bit with the triangular cut out) flip position when you operate the switch via the knob? Given that the switch has continuity in either position I'd say no, it isn't moving. There'll be a pin which engages in the 'V' shape or a similar arrangement to toggle the yoke. EDIT. Looks like one of the brass contacts may be bent? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

18th Jan 2021, 4:56 pm	#3
DonaldStott Octode Join Date: Aug 2015 Location: Glasgow, UK. Posts: 1,842	Re: EKCO U122 - Faulty on/off switch Thanks Graham - the link to your own earlier Post proved very enlightening and educational. My spring loaded pin was moving but the Paxolin 'yoke' wouldn't budge which meant that the two brass contacts were somehow stuck in place. Very gently eased them both up and the yoke now rotates with the spring loaded pin. Checked the external tabs with my DMM and everything is as it should be. Two images, switch on followed by switch off:- . Two further questions:- 1. I'd like to 'freshen up' the faces of the contacts and I've considered using a small strip of very fine wet&dry - will that be problematic in any way? 2 I need to reattach the disassembled switch parts using small bolts but need to ensure there is no snagging with the potentiometer slider - what size is recommended? I'll also follow Graham's advice and apply a small dab of silicone grease where shown - thanks again. __________________ BVWS Member

18th Jan 2021, 5:46 pm	#4
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: EKCO U122 - Faulty on/off switch I doubt the contacts will need cleaning but if you must use fine glass paper rather than emery paper/cloth. A squirt of Servisol wouldn't go amiss. I don't know about the size of bolts as the pot I repaired used bent over tabs rather than rivets. Same diameter of the rivets I guess. Aren't they insulated by holes in the hard plastic casing. I expect someone will be along to say that silicone grease shouldn't be allowed near electrical contacts as it creeps. All I can say is that I've never had any problems with it. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

18th Jan 2021, 6:04 pm	#5
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: EKCO U122 - Faulty on/off switch I've never had problems with silicone grease either, a tube of it was standard issue for lots of us TV service techs back in the day. Lawrence.

19th Jan 2021, 1:25 pm	#6
DonaldStott Octode Join Date: Aug 2015 Location: Glasgow, UK. Posts: 1,842	Re: EKCO U122 - Faulty on/off switch What I did was to use a 6BA tap to thread the hard plastic casing and inserted 6BA bolts from the tag side. I needed to ensure that the new bolts didn't snag the potentiometer slider so I've used my Dremel to cut them off flush with the inside face. The switch mechanism was secured first with masking tape to ensure that metal filings didn't fall inside. I'm thinking about a small dab of epoxy inside to secure the bolts? So far, so good ... And then we find that the potentiometer is playing up - I'm getting intermittent and inconsistent readings on my DMM as I rotate the shaft. I expect 0 - 500ohms or thereabouts but I'm getting nothing (reading 1 on my DMM) along most of the track and then the occasional 50-60 ohms! Tried cleaning the track carefully with Deoxit Fader F5 (good for things that slide rather than rotate) but this has made little or no difference. Can't see any problems with the track when examined closely with my loupe so not sure where this new problem lies? __________________ BVWS Member

19th Jan 2021, 1:29 pm	#7
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: EKCO U122 - Faulty on/off switch Bend the wiper so that it presses harder against the track? Test the track using one meter probe as a wiper. It's not unknown for the track to wear away. Often the wiper will have two or three points (inverted dimples) of contact with the track. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

19th Jan 2021, 1:33 pm	#9
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: EKCO U122 - Faulty on/off switch Ah yes. If the range used is too low ''1' can be displayed as an over range indication. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

19th Jan 2021, 3:03 pm	#10
DonaldStott Octode Join Date: Aug 2015 Location: Glasgow, UK. Posts: 1,842	Re: EKCO U122 - Faulty on/off switch Thanks Graham and Lawrence - the whole pot is a bit mucky, as is the rest of this set, so I'll give it a good clean with IPA and look at the track and wiper contacts again. I appreciate that it's a 500k pot so my DMM was on the 2M range but getting those strange readings! I'll report back later... __________________ BVWS Member

19th Jan 2021, 4:38 pm	#11
DonaldStott Octode Join Date: Aug 2015 Location: Glasgow, UK. Posts: 1,842	Re: EKCO U122 - Faulty on/off switch Ok 500k pot thoroughly cleaned with IPA - the track was really mucky indeed! Although I'm getting continuous readings with my DMM when I rotate the control I am, however, now reading 0-902k, almost twice what it should be? Looking at the circuit diagram (Trader Sheet 995) is it possible to adjust the value of any of the resistors associated with the volume control R9? __________________ BVWS Member Last edited by DonaldStott; 19th Jan 2021 at 4:53 pm.

19th Jan 2021, 6:57 pm	#12
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: EKCO U122 - Faulty on/off switch Any markings on it? It could have been 1M to start with. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

19th Jan 2021, 8:42 pm	#13
DonaldStott Octode Join Date: Aug 2015 Location: Glasgow, UK. Posts: 1,842	Re: EKCO U122 - Faulty on/off switch I've scoured all parts of this switch/pot with my loupe but can't find anything that indicates a value? It may have had a label on the side, evidence of residual glue, but this is long gone - some numbers are barely visible:- 34673/2 And on the base it has:- EGEN MADE IN ENGLAND 250V 1A That's all folks ... hope this helps? __________________ BVWS Member

20th Jan 2021, 10:00 am	#14
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: EKCO U122 - Faulty on/off switch What value of resistance do you read between the two outer tags 0f the potentiometer? __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

20th Jan 2021, 2:13 pm	#16
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: EKCO U122 - Faulty on/off switch I'd be inclined to try it in the set and see what happens. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.