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Dead Quad 34

Seanm

Seanm

pfm Member
Managed to kill it by switching it on while music was playing. There doesn't seem to be an internal fuse - don't suppose it's tucked away somewhere inconspicuous?
 
That certainly wouldn't kill it, i.e. it is not a factor in the fault.

There is a fuse on the rear panel in the IEC mains input.
 
Doh. Thanks both, yes, there the fuse is, clearly marked and accessible. Intact too.

Tony, yes, was surprised when that seemed to do for it: I got it partly because I'm prone to such lapses and I thought it would put up with a little abuse.

Off to Quad for repair I guess. Only serviced in 2013 so a bit disappointing.
 
What are the symptoms? Is it totally dead with no LED by the 'radio' input when it comes on? Can you hear any evidence of turning it on through the speakers, e.g. any slight increase in hiss?

As I understand it one of the Quad 34's weaknesses is the input switching circuitry, i.e. there is a chance it is mainly alive but with a dead control panel, and IIRC this is usually a capacitor issue, though if it is the chip or the board is damaged (by leaky caps) you are in some trouble. What version 34 is it? The earlier ones do apparently self-destruct to some degree as the multi-layer boards are prone to corrosion, the last two versions (board rev. -6 and -7) are far more reliable as the mainboard wasn't painted in the stuff that causes corrosion. Mine is a -6 and has a normal looking translucent glass fibre board so I'm hoping will have a good amount of time left!
 
Totally dead :(

Don't know how to ID the board but it's green, and it's the later grey, RCA model, although I think a fairly early example. Nothing obviously nasty inside.
 
The version is printed on the bottom of the circuit board, but if yours is a grey RCA one I'm pretty sure it will be a -6 or -7. The ones with issues are very obviously painted with some chemical in a very bright green/blue sort of colour (I'm colour blind so never trust me on these things!). I've never seen a pic of an RCA equiped unit with one. Boot it off back to Quad, Amplabs, Dada or wherever and get it sorted and I'm sure it will be ok.
 
unplug and Take the cover off plus the cover off the mains input area and take a picture they could be something obvious wrong
The Rifa X2 cap often fails on the quad gear but that usually blows the fuse as well as they often fail short, if your fuse is OK then its not that, it could still have gone but failed open so would have no effect on starting up.
If you are competent with a test meter then you could start testing without power that there is continuity through the power supply, then with power from the AC mains input, check the switch, check the output from the transformer secondary's (AC) check through the bridge rectifier if there is DC from that , check through the regulator if there is a DC voltage output

Alan
 
Here is some interesting info about the mainboard issues and other Q34 ills at quadrevise.eu. There are a few inaccuracies to my mind, e.g. they claim a -6 board has the laquer paint whereas mine clearly doesn't (it looks just the same as the rev-7 they picture bar a couple of very minor component changes). They are obviously trying to sell servicing, but there is a lot of good information on that page. Ken Rockwell's page is very good too (link) and there is a Stereophile review of the 34 here.
 
Tony L said:
What are the symptoms? Is it totally dead with no LED by the 'radio' input when it comes on? Can you hear any evidence of turning it on through the speakers, e.g. any slight increase in hiss?

As I understand it one of the Quad 34's weaknesses is the input switching circuitry, i.e. there is a chance it is mainly alive but with a dead control panel, and IIRC this is usually a capacitor issue, though if it is the chip or the board is damaged (by leaky caps) you are in some trouble. What version 34 is it? The earlier ones do apparently self-destruct to some degree as the multi-layer boards are prone to corrosion, the last two versions (board rev. -6 and -7) are far more reliable as the mainboard wasn't painted in the stuff that causes corrosion. Mine is a -6 and has a normal looking translucent glass fibre board so I'm hoping will have a good amount of time left!
Click to expand...

Isn't the main selector chip just a set of standard logic gates? Not checked so relying on my own lousy memory. The only cap that comes to mind is the one that pokes the arrangement at power-up to force it to pick one input as default. (Which I tend to shift as suits me anyway. :) ) Is that the cap you have in mind?
 
Thanks for the quadrevise link Tony. I hadn't realised that this board used the dreaded rivets linking top and bottom layers. No wonder there are problems. It would be interesting to do a modern drop in PCB for these units. It should be possible to keep the spirit of the design.
 
Jim Audiomisc said:
Isn't the main selector chip just a set of standard logic gates? Not checked so relying on my own lousy memory. The only cap that comes to mind is the one that pokes the arrangement at power-up to force it to pick one input as default. (Which I tend to shift as suits me anyway. :) ) Is that the cap you have in mind?
Click to expand...

No idea to be honest, I'm just kind of regurgitating things I've read rather than stuff I actually understand! Can you easily alter the input selected at power-up? I'd like to move mine to CD if it is real easy as I don't even have a tuner connected and it concerns me that I am wearing the switches by using them a couple of times most days.
 
Tony L said:
No idea to be honest, I'm just kind of regurgitating things I've read rather than stuff I actually understand! Can you easily alter the input selected at power-up? I'd like to move mine to CD if it is real easy as I don't even have a tuner connected and it concerns me that I am wearing the switches by using them a couple of times most days.
Click to expand...

Might be of help to you Tony:

http://www.dadaelectronics.eu/ForumRetrieve.aspx?ForumID=317&TopicID=481750&NoTemplate=False
 
One design weakness is the use of back to back 6V8 zeners on the signal inputs. Schottky diodes to the switch IC supplies with a small series resistor would have been a better protection without any risk of latch up. I guess BAT85 diodes were a bit too expensive back then.
 
Tony L said:
No idea to be honest, I'm just kind of regurgitating things I've read rather than stuff I actually understand! Can you easily alter the input selected at power-up? I'd like to move mine to CD if it is real easy as I don't even have a tuner connected and it concerns me that I am wearing the switches by using them a couple of times most days.
Click to expand...

Yes, its a trivial mod. Not checked but the webpage probably has it correct. IIRC The design essentially uses a set of standard inverters / flip-flops wired so that pushing a button selects the input you want whilst negating any that had been selected.

The action of pushing a button is imitated at start-up by the capacitor, which you can move.
 
Thanks, I may attempt it at some point.

I have a spare/donor 34 which is a bit of a Frankenstein job (long story) and I just took a look at it to see if I could easily spot the caps, but couldn't be bothered taking the front panel off to get to the control board. It will keep. I'm in the happy position of having a full spare set of switches, volume, tone, balance pots etc should my mint one ever go wrong. The reason I mention this is I was very surprised to see that the -222 mainboard in this DIN-equiped 34 (i.e. early) is the same translucent dark green of my -666 and the -777 pictured in great detail on the Ken Rockwell site, i.e. the board painting thing is not a simple correlation to revision. Very odd. It shows no evidence of rust or corrosion, though has a fair bit of damage from leaky caps that were replacec by Quad about a decade ago along with rebuilding some tracks the cap-goo had eaten. All rather ugly to be honest, but it did work last time I used it. I may just leave my good one alone and just replace the CD membrane switch if I wear it out.
 
IIRC the only dissassemble is to remove the case, and the cap is accessible. Bit fiddly, but should be quick and easy once spotted.

Personally, I like the earlier DIN versions. Simpler circuit and I prefer the colour scheme. :)
 
I suggest you taking advantage of this impasse: try a passive pre (or BTW a high-quality variable output CD player). It might well be you're not in a hurry to repair it... I've found a passive better than 33 or 34 when combined with Quad classic solid state power amplifiers as they have high sensitivity and input impedance.
 
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