Ekco U353 Restoration

[lesparapluies]

Thanks Frank, that's very helpful, will investigate further. Incidentally, I wonder if anyone else has spotted that there are 2 circuit diagrams available for this set, from different publishers, and there are subtle differences in the way the DM70 is connected between the 2, mine "agrees" with the "Trader" sheet

[Nuvistor]

I used the makers U353 circuit, do you need the Trader references?

Apart from some slight resistance value changes both the Trader and Ekco look the same, the U354 is quite different though.

[ms660]

Electrically they look the same to me (Manufactures and Trader)

EDIT: Post crossed.

Lawrence.

[lesparapluies]

It could be the way the wave-change switch is represented entirely differently in the 2 versions, but in these screenshots the anode of the DM70 is in one version fed from a resistor from the HT; in the other it also has another resistor going to earth. Also, the screen on one version is earthed through a resistor and capacitor R21 / C46, but I can't find that resistor in the other one. It probably doesn't help that in one version the values are all given but in the other they are numbered and you have to refer to the component list..(when I say earthed, I meant taken to chassis of course)

[Nuvistor]

The trader circuit is the same as mine but my makers circuit looks very different to the one you posted.

[lesparapluies]

Hi Frank could you send me a link to the maker's circuit please

[Nuvistor]

https://www.service-data.com/product...16/2199/m11516

The trader will give you as much information as the makers one. I have both because it’s on the DVD that available from the link at the top of the page.
By all means get the makers one but I don’t think you will find it helps any more than the Trader you have.

[lesparapluies]

Thanks again for recent replies. I didn't really get anywhere with the unresponsive magic eye; all the associated components seem to be OK, the voltages also and in this case I'm happy just to get the radio working, rather than it being a long-term restoration project. One thing which kind of spoils the performance is that the volume pot is very noisy towards the full clockwise position. When investigating the mains switch (see earlier posts) I did have to dismantle the pots and gave the tracks a clean at the time but there were still deadspots, as verified with an ohm meter. (I think the set had been stored in very damp conditions). I don't want to risk dismantling the pots again, and I don't think it's worth the outlay of having a new one custom-made. I was wondering if there's any mileage in putting a couple of high value resistors between the wiper and the two ends of the track, thus ensuring there's never an open circuit? (Please feel free to shoot me down in flames if this is a non-starter and I've overlooked something obvious!)

[lesparapluies]

Hello again. I got the problem with the noisy volume control sorted and for a few days the radio worked well, but another fault has developed. Sometimes the set goes into a very loud oscillation (actually I would describe it as white noise which all but drowns out the signal). In time-honoured fashion, a tap on the chassis with a screwdriver handle can stop it. However, the slightest vibration will set it off again, so much so that it's impossible to pin it down to a specific area, let alone a component. I've checked for dry joints with a magnifying glass but found nothing. This fault ONLY happens on AM, not VHF. I'm beginning to suspect it may be a faulty UCH81 mixer/oscillator valve. I don't have a spare to try at the moment but they seem to be fairly easily obtainable and I'll probably order one anyway. Does anyone have any further ideas as to areas to check? Thanks again, Mark