Quad 34 on blink - diyAudio
Go Back   Home > Forums > Amplifiers > Solid State

Solid State Talk all about solid state amplification.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 9th January 2004, 08:48 AM   #1
FM300 is offline FM300  Greece
diyAudio Member
 
Join Date: Jan 2004
Location: Olive grove
Default Quad 34 on blink

Hello all,

New user to diyaudio and would appreciate some help. I've "inherited" a Quad 34 preamp thats flaking out. Here's the short story:
Turn on, defaults to radio input selected, things ok.
Select phono, or tape things ok.
Select aux, and all the leds come on, albeit dimly.
Push buttons to try to get them off, lose sound, and source selected.
Turn off, turn on, and comes on with the leds all selected again......

I dont have a shematic, but seems there's some driver transistors for the leds, they seem ok.
Next in line is a 4001 cmos switch. Maybe this is the culprit, but figure I'd ask before I start ripping out surface mounted chips...
The friend that gave me this also has a 34 that does this very rarely....

Also, about a year ago I replaced some of the electrolytics in this thing for my friend as an attempt to cure this w/o any success.

FWIW, SN is 6277
Anyway, would appreciate any help. Is it out of line to ask for a schematic here?
While on this, any mods out there to improve the sound of this thing. I see alot of tl071's in there....
Member ACD posted a while back that he has modded his Quad 34...

regards, and thanx,
  Reply With Quote
Old 9th January 2004, 10:27 AM   #2
diyAudio Member
 
Jan Dupont's Avatar
 
Join Date: Apr 2003
Location: Copenhagen, Denmark
Send a message via MSN to Jan Dupont
Default Nicolas

I've have just send you an email
Help is on the way...
__________________
Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com
  Reply With Quote
Old 9th January 2004, 01:45 PM   #3
johnm is offline johnm  United Kingdom
diyAudio Member
 
johnm's Avatar
 
Join Date: Sep 2003
Location: Hampshire
Hi! I'm new to DIY Audio as well! I've just had exactly the same problem occur with my Quad 34. Would you be able to e-mail the same files please? Many thanks!

- John
  Reply With Quote
Old 9th January 2004, 03:06 PM   #4
diyAudio Member
 
Jan Dupont's Avatar
 
Join Date: Apr 2003
Location: Copenhagen, Denmark
Send a message via MSN to Jan Dupont
Default John

I'll put you on my list
__________________
Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com
  Reply With Quote
Old 13th January 2004, 09:54 AM   #5
FM300 is offline FM300  Greece
diyAudio Member
 
Join Date: Jan 2004
Location: Olive grove
Default Resolved; Thanx ACD

hi,

Thanx to ACD for supplying a schematic.
The 34 is now fixed. The problem was that a couple of electrolytics had leaked (not obvious), and tracks were shorting. Mine were C77 & 78, the 100 mic. output de-coupling caps.
The ooze had effectively also "eaten" part of the tracks and tiny jumpers were soldered in to restore continuity.
I cant believe that Quad used such ****** caps in the audio path.
I will now try, as recommended, to short all the decoupling caps, see for dc offset at the outputs, and either go with this, or use film caps at the outputs.

I wonder how much dc drift is acceptable///but I guess that answer might be what amp are you driving....

WRT to chaniging the tl071's, any chip recommendations? A friend really likes the 5532, but again IIRC, this is a fairly old chip also...

anyway, on to repairing the Cambrdge P50,

thanx again,

nicolas
  Reply With Quote
Old 13th January 2004, 10:45 AM   #6
diyAudio Member
 
Jan Dupont's Avatar
 
Join Date: Apr 2003
Location: Copenhagen, Denmark
Send a message via MSN to Jan Dupont
Exclamation Nicolas

It is NOT the decoupling caps you should shorten, but the AC coupling caps in the signal path
__________________
Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com
  Reply With Quote
Old 13th January 2004, 01:39 PM   #7
FM300 is offline FM300  Greece
diyAudio Member
 
Join Date: Jan 2004
Location: Olive grove
Hi Jan,

I'm bumbling my terminology , This is what I am contemplating/have done;

I've shorted C3-8, the input (ac-coupling) caps for the sources.
I'am getting ~2.5 and -5.0 mv at the output of IC3 and 4, which goes to the aux
DIN (nowhere?). I dont know Quad/DIN philosophy. Are these mv ok, if not, I'll leave C16, 17 there.
I believe, this type of connection might have been to allow a second cassette to be used via the aux..

Anyway, at C77, C78, the decoupling caps for the outputs, I get 0.4 mv, and -1.7 mv.
Are these levels ok? I should probably leave these in for good measure.

Any other caps in here I should be looking at?
C30 and C31 I have also shorted.

Finally, what are the common gate, T14 and T15 at the output for? They seem to be in parallel
with the outputs of IC19 and IC20????

Anyway, thank you very much for your help,

regards,

nicolas
  Reply With Quote
Old 13th January 2004, 03:21 PM   #8
diyAudio Member
 
Jan Dupont's Avatar
 
Join Date: Apr 2003
Location: Copenhagen, Denmark
Send a message via MSN to Jan Dupont
Hi Nicolas,
You missed C36/C37
I think the AUX was attented for a second taperecorder or so (I don't use the output).
Just leave C16/C17 in there, or change to new better quality if you plan to use the AUX output.
Your mV on the output are not bad, but just replace C77/C78 to a better type (I have a switch, so I can choose between AC and DC coupling of the output - no major difference ).
I also shortend C48 and C54 on the output of the Tilt controls.
The two transistors T14/T15 works a "Mute-Circuit", shortly connecting the output to Ground, when you use the input selector (to prevent nasty sound to go to your power amp).
Hope this have helped.
If not! Just ask
__________________
Free Schematic and Service Manual downloads www.audio-circuit.dk, Company: www.dupont-audio.com, Joint venture: www.DupontMantra.com
  Reply With Quote
Old 4th February 2004, 10:18 AM   #9
diyAudio Member
 
Join Date: Feb 2004
Location: near Amsterdam
My Quad 34 has developed a similar fault recently, but with the tape loop circuitry.

When pressing the 'Tape' button, the associated LED lights very dimly, becoming increasingly brighter over the time the tape loop is engaged, but it never reaches normal brightness, it remains dim.

Until a few days ago, the tape loop functioned properly regardless of this problem, but it now stopped working altogether.

I presume that, similarly to FM300's problem, some capacitors have dried out and need replacement, but which ones?

Any help much appreciated!

Kind regards,

Frank
  Reply With Quote
Old 4th February 2004, 12:59 PM   #10
FM300 is offline FM300  Greece
diyAudio Member
 
Join Date: Jan 2004
Location: Olive grove
Hi,

Check for "goo" and ooze on the pc...

regards,

nicolas
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Quad 405 hum AndrewGM Solid State 26 4th November 2008 10:11 PM
Quad 44 vento Solid State 11 27th October 2008 09:05 AM
Quad 33 Please Help me !!! puska Solid State 0 22nd October 2008 06:01 PM
BGW Pro 250E on the blink DanGriffing Solid State 1 23rd September 2008 06:59 PM
quad 405 hazenhoe Solid State 2 27th December 2003 01:32 AM


New To Site? Need Help?

All times are GMT. The time now is 02:43 PM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2