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Old 15th Feb 2019, 8:36 pm   #1
Vintage_RC
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Default Pye Q4 wavechange switch problem

I have a Pye Q4 lift up lid early transistor portable which works on MW but not on LW. I decided to investigate the problem today, I used another set to listen to the local oscillator (LO). It was evident that when I changed from MW to LW the LO didn't change frequency so suspicion immediately fell on the wave change (WC) switch. A look at the circuit and the wiring showed the contacts where the problem might be and a poke on the suspect contact with an insulated tool made the LW work. I have attached a photo of the WC switch with a ring around the problem contact. The problem is how do I close the contact gap above and below without a messy dismantling of the whole wafer switch assembly? Another point not helping is that mating face that the contacts should touch does not seem to project as far out as it should when compared with other parts of the switch assembly.
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Old 15th Feb 2019, 9:42 pm   #2
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Default Re: Pye Q4 wavechange switch problem

Hi Alan, statement of the blooming obvious perhaps but have you tried a squirt of switch cleaner? Since the contacts are easy to get at you might try squirting some onto a cotton bud and gently wiping the contacts. Looks like there is a lot of oxidation there. It isn't usually a good idea to start bending the contacts as that can end in irreparable damage to the switch. Cheers, Jerry
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Old 15th Feb 2019, 9:52 pm   #3
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Default Re: Pye Q4 wavechange switch problem

I have recently tried a can of WD40 - no not the original stuff but quick drying contact cleaner and so far it works really well.
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Old 15th Feb 2019, 11:24 pm   #4
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Default Re: Pye Q4 wavechange switch problem

Quote:
Originally Posted by cathoderay57 View Post
Hi Alan, statement of the blooming obvious perhaps but have you tried a squirt of switch cleaner? Since the contacts are easy to get at you might try squirting some onto a cotton bud and gently wiping the contacts. Looks like there is a lot of oxidation there. It isn't usually a good idea to start bending the contacts as that can end in irreparable damage to the switch. Cheers, Jerry
Yes I had tried a quick squirt of Electrolube to no effect. Regarding your commenting about bending the contacts, on close examination it looks like someone has at some stage in the past done just that. When I gently push down on the contact there is a small but perceptible movement suggesting there is a physical gap. This is looking like a tricky one to solve.
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Old 16th Feb 2019, 1:09 am   #5
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Default Re: Pye Q4 wavechange switch problem

It is indeed sometimes possible to increase the bend angle on the contact fingers, using tweezers or pointed pliers. Go easy, using a prod of some sort to hold the rivet side of the bend flat. Check for loose rivets etc first. Bending does not work if the metal has lost its spring and there is a risk of breakage but I have had reasonable success.

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Old 16th Feb 2019, 7:16 am   #6
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Default Re: Pye Q4 wavechange switch problem

Personally I wouldn't hesitate to try bending the contact and have done so successfully on a number of occasions. After all, how else do you deal with a bespoke wafer switch in a long obsolete piece of equipment? Also, there's not much to lose since the switch isn't working anyway. I would slip a darning needle under the contact arm and apply light pressure to the contact itself. Loose rivets can often be tightened with a small pair of pliers or even a carefully applied blob of superglue if access is a problem.

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Old 16th Feb 2019, 10:34 am   #7
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Default Re: Pye Q4 wavechange switch problem

Replacement wafer switches are available but you'd no doubt have to figure out how to wire it and cut the shaft to fit etc. There's a 6-pole 2-way at Farnell here; that's just the contact set - the shaft and carrier assembly is extra so when you add it up it's fairly expensive. https://uk.farnell.com/nsf-controls/...-switch-wafers . Good luck
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Old 16th Feb 2019, 11:13 am   #8
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Default Re: Pye Q4 wavechange switch problem

Gentle scrubbing with a fibreglass pencil followed by a few dabs of DeOxit.
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Old 16th Feb 2019, 6:21 pm   #9
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Default Re: Pye Q4 wavechange switch problem

As I intimated earlier the problem is not one of cleaning but that the contacts are not touching the wiper. I have come up with a simple solution using part of a bent pin. OK it's a bit crude but it works. See photo.
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