Ekco U353 intermittent VHF

[Pat Pending]

Of all the other radios that I've repaired without a second thought, and it's the one that used to belong to my dear ol' departed Dad has got me flummoxed!

When listening to VHF, the sound drops out with an audible plop, only to return a few seconds later. Its OK on MW and LW. I've changed the suspect caps and subs'd the tuner valve (no hiss when it happens) HT present and correct when fault is happening. Haven't  been able to try anything else cos' it won't stay broke !

Any ideas?

This is only repair #2 in its 56 year life, I wish I could say the same for myself!

Thanks. Andy.

[Geordie McBoyne]

Information for the Ekco U353 can be found in the 1960/61 Radio and Television servicing book, pages 82 and 83.
Tricky faults to find. The problem could possibly be caused by one of the the three 15pf tuning capacitors in the 10.7mc/s IF transformers. The secondary of the final 10.7mc/s transformer is tuned by a 22pF capacitor.
Have you checked or replaced the UABC80?

Geordie McBoyne.

[Pat Pending]

I've now tried the UABC 80 (on your suggestion) still the same. I don't fancy digging out the IF cans tonight but it sounds plausible. I'll have another go tomorrow evening, thanks for the options.

Regards, Andy.

[pilot mariner]

I've just had a very similar fault on a Grundig (my post is a couple down the list). Turned out to be an intermittent 25pf cap in one of the IFTs.
I tracked down the faulty stage by tuning into the 10.7Mhz IF on a scanner then enabling/disabling each stage by pulling the valves till the fault disappeared. Once the faulty stage was identified many components could be ruled out as they were used on AM only, this just left a few components to check . However I appreciate this may be difficult with your set if it has series heater valves, but maybe you could disable each stage some other way. It saved alot of time in the end.

Mark

[Pat Pending]

You're both quite correct! It was an unsoldered joint in the first IF can (traced with the 'scope), what is really amazing is that it took 56years to cause a problem. Thanks Geordie, Thanks Mark, much appreciated.

Regards, Andy.

[ppppenguin]

Unsoldered joints can work OK for very long periods. I once had a small video monitor with an intractable intermittent problem. A heater connection to one of the valves had never been soldered. Must have worked OK for at least 20 years.