Pye PE80. Local oscillator prob.

[vintage_8bit]

Hello all.
I now have a Pye PE80 on the bench. I have changed the 2 decoupling caps on the output stage and changed or checked the electrolytics.
All is working well apart from the last 6 S.W. high frequancy wavebands. When the wavechange switch is slightly rocked it goes off tune. This also happens if you apply pressure to the wavechange switch anywhere or even the wavechange switch metal mounting plate.

I am observing the L/O with my SDR radio. With no signal on the front end of the Pye. When you apply pressure as mentioned above you can clearly see it moving up and down in frequancy and staying at its new shifted frequancy. It can change around 20 kHz

I have cleaned the wavechange switch several times with servisal and compressed air then washed off with isopropanol. I have closely examined the contacts around the L/O and the input side of the mixer and all seems in good condition. I am wondering if its an earthing problem. I also wondered if the tubular spacers separating the wafers could cause problems. Particularly when they are right next to the sensitive terminals of the L/O. The earthing on some tubes is hit and miss depending on how close to the threaded bar they are.

Hope that all makes sense.

[vintage_8bit]

Fixed! I think. I loosened the retaining nut on one side of the wave change switch, this was very tight. I then rotated the tubular spacers and retightened. The reason I was suspicious of these is because I could see the resistance to earth changing on the spacer between the L/O wafers, when anything was moved as in my 1st post above. If anything is placed near this area on the higher frequencies it will pull the L/O off frequency. So I reasoned that having something metallic this close with a changing resistance / inductance to earth was not good?

Next question.
What's the best way to loosen the slugs in those transparent plastic tubes. They all appear jammed. I may get away with just adjusting one, if its to risky damaging the slugs. They look untouched from manufacture.

[Andrew2]

Well done on finding the cause of the frequency jumping. I had a similar thing with an old Kenwood transceiver which used a non PLL local oscillator. It turned out to be the screws that held a screening can in place.
For the slugs, I suggest gentle heat from a hair drier to soften the aeons-old grease or wax that was used to hold the cores in place.

[vintage_8bit]

Thanks Andy. I did wonder about posting this and the fix, as it seemed a bit far-fetched. I still can't get the fault to return so im happy.

I just found that the second to last shortwave waveband has its L/O frequancy tuned on the low (wrong) side of the signal, but otherwise the set seems ok.

Its the only radio I have here, that makes Radio Caroline listenable. The tone control, after changing a couple of caps is also quite affective.

Colin

[vintage_8bit]

After applying heat from a heat gun positioned about a foot away, I finally managed to loosen and remove slug unmarked. The slug seemed to be held by a black substance, pitch or varnish? I think originally it also had a fine length of rubber down the side of the slug. It was very tight. In the past I've usually applied heat to just the slug, but this time it didn't budge. So, L/O now adjusted & chassis is now ready for its case when its varnished and painted.

Can anyone tell me the type of finish on the black painted areas of the case?.

Colin

[music-centre]

Hello Colin,
Well done in getting it fixed, I have 1 of each of these with the 2 different dials that were fitted,the finish on the sides is just gloss black paint.
Steve.

[vintage_8bit]

Thanks Steve. The sides on mine are quite dull and crazed so I couldn't tell what the original finish was like. Thanks to all, for your help.

Colin.