Jim Lesurf wrote:



if this is intermittent, then I'd suspect that there is an unreliable power
or reference level connection. Possibly to the board at the front of the
set that holds the switches, etc.
Thanx,
I'll check this....

The actual signal switching is done using 4066 CMOS switches (at least in
issues 1 - 3 of the amp). However some other logic is used to control this
and (when working correctly) ensure only one non-tape input can be selected
at any time. That would probably be the failure point as the LEDs are also
driven from this. The transistors here are simply to give enough boot to
light the LEDs, I think.
Thanx for the reply,
I tested the transistors and they seem ok, and yes I think they are
drivers for the leds. I will next replace the 4066, as I see thats next
in line. As for "some other logic" controlling the inputs, I am at a
loss here......

If no-one else has a diagram to hand, ask again and I'll see if I can
produce a scan. Do you know what issue of board you have? (Or can say the
serial number.)
Thanx, a schematic would be great. I found a 44 schematic on the web,
and trying to cross reference that to get an idea as how this thing
works, but it's a pain....I dont even know how similar they are...

I can tell you the serial number tomorrow...

thanx again..

regards,
nicolas


BTW, does this thing sound ok? I am a bit put off by all the tl071
opamps that populate this thing. Aby recommended mods?


I find the 071's work fine and would not personally change them.
Replacement with a different IC might lead to other problems. However I do
change some other components to alter the action of the 'tone controls' a
little. You can also easily change which input is selected by default by
moving a capacitor. :-)

Slainte,

Jim

Chris Morriss wrote:


In message , nicolas
writes



I replaced those with OPA604s in my 34. It lowered the noise level but
that's about all.

I have the service manual for the original DIN socket version. I don't
have a scanner but my brother has one. I could scan the schematic in a
weeks time or so for you.
Hi,
Thanx for the offer; that would be great. Mine has the DIN sockets also..

regards,

nicolas

Chris Morriss wrote:


In message , nicolas
writes



I replaced those with OPA604s in my 34. It lowered the noise level but
that's about all.

I have the service manual for the original DIN socket version. I don't
have a scanner but my brother has one. I could scan the schematic in a
weeks time or so for you.
Hi,
Thanx for the offer; that would be great. Mine has the DIN sockets also..

regards,

nicolas

Hi,

FWIW, the Serial Number on this preamp is 6277

regards,

nicolas

Hi,

FWIW, the Serial Number on this preamp is 6277

regards,

nicolas

Hi Nicolas!

I heard from Quad themselves that this problem is caused by leaky
100uF electrolytic capacitors in the 34 - unfortunately I do not know
which ones. Quad serviced my 34 a few years ago now, and when it was
returned all the 100uF caps had been replaced, and portions of the
circuit board appeared to be lightly sanded down, perhaps to clean any
damage caused by the leaking caps...

Hope this is of some help, but if not please e-mail Quad themselves -
they've always been very helpful in answering questions of this
nature. I think it's

Let me know if you manage to repair the fault, as mine has now started
doing the same after beign OK for two years :-(

All the best,

- John.




(nicolas) wrote in message om...
Hi,

I inherited a Quad 34 pre that weirds out now and then. The preamp
comes on, with the default source selected. Either by itself, or when
selecting another source, all the selector leds light up dimly, and
the sources are lost (pre does not work).
Any one have a schematic that they may scan for me. It seems that the
tactile switches drive a row of 8 transistors that probably do the
switching part...

would appreciated any help.

BTW, does this thing sound ok? I am a bit put off by all the tl071
opamps that populate this thing. Aby recommended mods?

nicolas

Hi Nicolas!

I heard from Quad themselves that this problem is caused by leaky
100uF electrolytic capacitors in the 34 - unfortunately I do not know
which ones. Quad serviced my 34 a few years ago now, and when it was
returned all the 100uF caps had been replaced, and portions of the
circuit board appeared to be lightly sanded down, perhaps to clean any
damage caused by the leaking caps...

Hope this is of some help, but if not please e-mail Quad themselves -
they've always been very helpful in answering questions of this
nature. I think it's

Let me know if you manage to repair the fault, as mine has now started
doing the same after beign OK for two years :-(

All the best,

- John.




(nicolas) wrote in message om...
Hi,

I inherited a Quad 34 pre that weirds out now and then. The preamp
comes on, with the default source selected. Either by itself, or when
selecting another source, all the selector leds light up dimly, and
the sources are lost (pre does not work).
Any one have a schematic that they may scan for me. It seems that the
tactile switches drive a row of 8 transistors that probably do the
switching part...

would appreciated any help.

BTW, does this thing sound ok? I am a bit put off by all the tl071
opamps that populate this thing. Aby recommended mods?

nicolas