Quad 34 advice

[ITAM805]

I have my first ever Quad on the bench, but furthermore, I've witnessed my first live RIFA mains filter self destruct inside it - what a stink !

This control unit from 1983 has been standing for several years as a non runner. I found the fault, a missing -7.5V rail due to a corroded trace. Bench testing it's all working into the accompanying 303 amp, but after an hour it started getting a bit hissy, the 303 is dead quiet so it's something in 34

Also when switching the inputs or filters it produces a loud pop in the speakers, cant be right on a piece of kit like this surely? What would cause this?

The caps look ok with no sign of leakage, but it is getting on in years

Any advice regarding this unit would be most welcome. Also should I bother replacing the RIFA

Many thanks

[Ted Kendall]

Best to replace the Rifa with a polycarbonate. I agree about the stink - it's indescribable! I had five go off almost at once in a Revox...

If the 34 has got damp enough to corrode a trace, I'd dry it out in the airing cupboard or over a radiator for several days at least before chasing other causes.

[alanworland]

My Quad 44 that I have just fitted a Dada kit in didn't include the rifa but when I opened up the power supply it had obviously swollen and started to split so I don't think it had long on this earth!

Alan

[ITAM805]

Thanks Ted, have ordered a polycarbonate

Regarding the corrosion, most of the board looks clean so I dont know whether it's spillage or some of the caps have leaked? I jumped the gun saying the caps looked good, they do, but the 3 of the 4 I've pulled are knackered

[ITAM805]

I recapped this board but there was still a fault. The source switching was all over the place, jumping from one to another and making pops and crackles, so I assumed IC11 (CD4001BE) was faulty. Also if I hold the Aux button in the led goes brighter, is that normal? The +/-7.5V rails are present

So I fitted a new 4001 today but it's still faulty. If I apply a signal into 'Aux' it works but after a short while it disappears and re-appears if 'Radio' is selected. When I switch back to Aux there's just noise?

I see that Aux and Radio inputs are switched by IC2 (CD4066BE) could it be this?

[Radio Wrangler]

You might want to take a jaundiced look at those megohm resistors.

David

[nutteronthebus]

I have had that chip go faulty on my 44 and 1 tape input had audio breakthrough on one channel no mater what was selected . if you want a couple ( I bought 25 from RS ) PM me

Dave

[Radio Wrangler]

CMOS had a problem - purple plague corrosion.

TTL ICs dissipated enough heat to drive moisture out, but CMOS didn't. Moisture got onto the glass passivation layer over the chip and leached phosphorus out of it. THe phosphoric acid formed attacks the aluminium conductors on the surface of the chips. They go intermittent an then exhibit a hard fault.

Later parts were made better.

I have a rather good IC-765 I need to fix. It's a failed CMOS gate.

David

[ITAM805]

Thanks David, the 1M are all ball park. And thanks for the cmos info too.

Dave PM sent

[ITAM805]

Firstly, a big thanks to Dave (nutter) for the 4066 chips which came today. I swapped out IC2 but unfortunately the fault persisted

So head scratching time, having replaced the gubbins of the source selection/mutes circuit, what else could it be?

Going back to the original fault of corroded traces I wondered were there more? Checking for continuity, the traces between IC11 and IC2, two were open circuit ! So I rewired both chips and it's now working

Letting it stew now just in case there's more ...

[nutteronthebus]

Hi I am glad you found the fault I had the same type of fault on my 66 pre amp where it was O/C from the remote receiver to the main board and would not work at all

Dave