Monday, 13 May 2019

Ekco U353 - a quick restoration.

Ages ago Steve was good enough to bring up Sam's Queen Anne for some repairs. Also in the boot of Steve's car was a broken Ekco U353. Now, I have one of these, (see here!) which I repaired ages ago. It's a basket case, and remains unused as it's knobs are missing.  The knobs are an essential electrical safety item, as the chassis is connected directly to the neutral of our mains supply (common practice back then).

Anyway here's Steve's...

Much better nick than mine, although there's a crack to the right hand side of the cabinet... 

... and the back's a little distressed where the heat from the rectifier and output valve has made the back brittle, and damage has occurred. Some of the brackets are in poor shape too.

Removal of the chassis is straight forward, off with the knobs (there are two small grub screws to undo), and removal of four screws on the underside of the case.

It all looks very clean and unmolested.

Amongst the dust in the bottom of the cabinet, a tell-tale blob of wax shows something's been getting hot...

... and sure enough ...

... C61 has had a right sweat on! As usual, these waxy caps will all be shot, if not now, in the very near future, and will all be evicted. C61 is the mains input filter cap, so it's replaced with a brand new X2 class safety capacitor. It's 0.01uF.

Now in my example, the output valve had been cooked as the cathode bypass capacitor had failed short, so this is also replaced. In fact there's very few capacitors in the whole receiver, so every electrolytic, paper/wax and hunts capacitor is replaced, except the main multi-section smoothing capacitor.

The cathode bypass capacitor is C55. C50, C49, C46, C1 and C20 are all replaced. C1 is a horrible black hunts thing.

After the caps are replaced, it's time for action. The receiver is connected to the variac, and the voltage slowly increased for about an hour, monitoring the HT voltage, and periodically checking the temperature of the main multi-section smoothing capacitor to see if it's getting warm. It wasn't.

After a quick tune about, stations are coming in, and the FM seems to working too. The receiver is aligned in accordance with the service sheet, and it's performing well, except the exclamation mark magic-eye isn't illuminated :(

R14 (68K) has risen in value to many megohms, and crumbles as I remove it! After it's replaced the exclamation mark works as it should.

The guilty parties!

... and the elusive knobs ...

A piece of car body re-enforcing mesh is cut out to cover the damaged areas of the back...

... and it's filled, drilled and painted. Not the tidiest job in the world, but it'll render the set electrically safe, and allow the required ventilation.

The set's plug is fitted with a more suitable 3A fuse (there's another 13A fuse I've gained!!) and it's reassembled and given a nice long soak test.

Another saved from landfill :)