Roberts R600: Fades

[Mike Watterson]

Roberts R600 mysteriously dies.
Sometimes nothing happens when you turn it on.
Sometimes it fades out when you turn it on.
Operating the buttons can bring it back, so I thought at first it was dodgy wavechange switches, except I'm sceptical now. Because the first "wreck" one I got definitely did have unrecoverable switches apart from the IF module being dead.

Sometimes it's fine when you turn it on.
When it's fine, it's very good on all bands and loud. Also seems to keep running till you turn it off.

When it's dead, it's like there is no battery.

Any suggestions?

[ppppenguin]

Normal faultfinding. Check the DC conditions when it has faded out. That should show which stage(s) are in trouble. Except that once you've got the covers off and are probing it, the wretched thing will work perfectly. Until you put it back together.

[Murphyv310]

Yes.
It will never go faulty with the covers off.
Check silly things like battery connectors especially soldering or even missed or solder that hasn't taken. Even the B16T had a perfectly good looking joint but the actual valve connection was totally dry from the factory.

[ppppenguin]

If there's a slow fade then it's fairly certain that an electrolytic is involved somewhere. Perhaps with a bad contact on a bias resistor. Unlike the little 9" valve video monitor I once had with intermittent slow field collapse. That was heater connections to the field output valve that had never been soldered.

[Mike Watterson]

I'm thinking it sounds like loss of HT to large electrolytic.
At least it's only 9V and no glowing bits.

It's not always perfect outside of the cabinet. It's a shame because it's lovely when working. Totally dead this morning. Then on third attempt brief life. There may be two faults as just now there is faint hiss, clicking the wavechange brought back operation.
Now it seems fine.

I bought this because either it or the R700 was the last set my Grandparents had. I bought the R600 too. In the early 1990s my grandfather died in the nursing home (he wasn't particularly unwell, but in his 90s). My mum had previously chucked out anything in their flat she didn't want and at that point dumped his Roberts radio. "It was old."
Our first TV and radio were their cast offs. A big console TV with doors about 1959 or 1960. Then a big AM/FM radiogram with hinge out record storage. Maybe an RG101. My dad decided to take it to my other grandfather as he'd got a Murphy "batwing" AM/FM set and we had a KB toaster in the kitchen. We also had some sort of home made turntable that curiously had a lamp inside the box. It was not long after the start of the M2 was open and it was on the roof rack of a Simca, another cast off from my mum's parents. It came off the rack on the motorway. The cabinet totally came apart at all the seams. So we loaded all the bits into the boot and said nothing to grandpa. I was allowed to keep the parts, except the cabinet. The valves, scale glass and radio chassis was fine! I forget what became of it.

[Murphyv310]

Sounds like a three legged fuse breaking down. Even touching the base of the naughty component with a screwdriver can wake them up. A quickie repair. I expect a result by noon, if not you'll be sent to fit new painter chips in Philips TV sets as a punishment.

[Mike Watterson]

It's back in the WS, but I got distracted by the idea of a B7G battery valve tester. I have a spare piece of Murphy B283. But…
The late night Murphy Madness.

[Mike Watterson]

It might have been a dry joint where the very short wire power switch on the back of the volume control connects to the PCB?

Only time will tell.

[Mike Watterson]

It's not fixed though if left on it may come to life.

[Murphyv310]

Freezer spray often finds obscure faults, not just semiconductors etc but even dry joints by contraction.