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Vintage Amateur and Military Radio Amateur/military receivers and transmitters, morse, and any other related vintage comms equipment.

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Old 11th Sep 2020, 8:48 pm   #1
G6Tanuki
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Default Pye AC200 power-unit rework.

I've been restoring a well-used one of these to serve as a 'home' for a 144MHz-converted MX290.

Things didn't go well: though it worked fine when fed with +12V to the 'backup battery' terminals (even the nice green-glowy VFD in the front-panel clock seems healthy) when I tried mains-power I got nothing, followed by 'a nasty smell'.

One of the two PSU diodes had disassembled itself impressively - further investigation showed that the big blue electrolytic cap was a total-short.

I've got a new electrolytic on order, and have decided that the easiest replacement for the failed diode is to use two of the diodes in a nice big metal-cased 30A-rated bridge-rectifier I have conveniently to-hand.
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Old 12th Sep 2020, 9:57 am   #2
Jon_G4MDC
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Default Re: Pye AC200 power-unit rework.

If the transformer is OK you have got away with it.
They were good units.
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Old 12th Sep 2020, 10:10 am   #3
CambridgeWorks
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Default Re: Pye AC200 power-unit rework.

I might have the service sheet somewhere. Let me know if wanted. Pye Telecom transformers were always extremely well made and very reliable. The only exception for some reason was the AM Westminster W15 mod transformer (AL21219) that occasionally went shorted turns. In my time, I must have changed 8 or 10. Never any other transformer in their range of gear afaik went faulty in my experience.
Rob
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Old 12th Sep 2020, 10:19 am   #4
Jon_G4MDC
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Default Re: Pye AC200 power-unit rework.

Thanks for that gem Rob. That might explain a difficult W15AM I came across. I never could get the mod right but I hadn't thought of that. Hmm - I wonder if I still have it?

Sorry it's OT but I couldn't resist.
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Old 12th Sep 2020, 11:23 am   #5
sentinel040
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Default Re: Pye AC200 power-unit rework.

I have had to repair two of these AC200's and in each case it was the small potted transformer used to provide power to the switching IC going shorted turns.

Ian
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Old 13th Sep 2020, 3:41 pm   #6
CambridgeWorks
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Default Re: Pye AC200 power-unit rework.

Got to be 25 years since I had the lid off one, but surely the AC200 is a linear psu? Big transformer and with power transistors on a rear heatsink? The AC290 is a switching psu, the size of an M290 series mobile.
Jon, ot, but the shorted turns fault gave hardly any modulation at all.
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Old 13th Sep 2020, 7:09 pm   #7
Jon_G4MDC
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Default Re: Pye AC200 power-unit rework.

Thanks Rob. Ur confused about 200/290 same as me.

I had the 290 version (one might still be in the junk pile). Switch mode.It was RF noisy so I cut the plug off it.

It was very well made (Farnell I reckon) but they were early days for SMPSUs and RF EMC. Mine was in the same die cast aluminium sleeve used for M293/4 etc series. (Compare that with the MX290 series die cast, compartmented, chassis with top and bottom lids)

The AC200 had a nice green fluorescent display digital clock didn't it? Standard Pye speaker guts were mounted to fire out of the side. Marvellous. The AC290 was just a PSU I think.

Or have I got the wrong unit?

[ W15AM mod transformer chatter had better be another thread ] Mod edit: https://www.vintage-radio.net/forum/...d.php?t=171017

Last edited by Jon_G4MDC; 13th Sep 2020 at 7:18 pm.
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