Quad 44 Mk 3 upgrade help

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10-Mar-2019 09:00 AM

barkersoldbean

barkersoldbean

Posts: 22

I've finished upgrading the tone board (5 X ICs, 6 Caps) and tested it. I'm getting perfect sound out of the right channel, but ~1/4 volume out of left and some distortion. Checked the ICs (3 needed soldering, 2 were push fit) under high mag and tracks seem to be clean (i.e. no solder crossing over tracks)?

Would be good to know which ICs were part of the left channel and then might think about remove and refit the soldered one(s). 

Any suggestions to troubleshoot very welcome - it is getting close - if not already at - my pay grade for electronics (i.e. i can solder but don't know much else).

(Might have to ship it to Antwerp and let a real expert do a proper job)

Tony

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11-Mar-2019 01:30 AM

EJP

EJP

Posts: 1559

Starting from the one on the edge of the board next to the volume control, they run IC700,1,2,3,4. Note that some of them are used for both channels and others aren't.

EJP

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11-Mar-2019 10:46 AM

barkersoldbean

barkersoldbean

Posts: 22

Thanks - any way of knowing which are specific to the left channel and which are shared?

That way I can focus on the ones specific to the left channel.

Tony


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11-Mar-2019 11:14 AM

EJP

EJP

Posts: 1559

It's in the schematic. For example you have IC700A and B. The schematic for the Mk III tone control board is in the 44 service manual in the Downloads section.

EJP

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12-Mar-2019 09:35 AM

barkersoldbean

barkersoldbean

Posts: 22

Thanks for this - but I confess to being a bit confused? The circuit diagram I have indicates 4 ICs - and my Tone board has 5 of them - two in holders and 3 "naked". does anyone have an updated schematic for later tone control boards?

(I've scoured the internet to no avail)

Tony

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12-Mar-2019 10:01 AM

barkersoldbean

barkersoldbean

Posts: 22

The board is a 12784-2

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12-Mar-2019 10:23 AM

EJP

EJP

Posts: 1559

I've already answered this. All the relevant Quad 44 schematics are availablehere, in the Quad 44 service manual in the Downloads section. That's what I was looking at when I answered your question.
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12-Mar-2019 11:01 AM

barkersoldbean

barkersoldbean

Posts: 22

Humble apologies - I've got it.

Sorry for being a blind twit.

Tony

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12-Mar-2019 12:52 PM

barkersoldbean

barkersoldbean

Posts: 22

Ok - final question and then I can get on  with things....

I have found the schematic for the tone control board (12784-2) in the download section but what I need is a full visual layout and component numbering for the actual board (i.e which component is which so I can tie in the schematic with what I see visually)

In the service manual it doesn't show it for my board and on the upgrade manual it only indicates a few components but not the location of each IC. 

Any help very welcome.....

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13-Mar-2019 12:51 AM

EJP

EJP

Posts: 1559

I've already told you the location of each IC above.

EJP

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13-Mar-2019 11:02 AM

barkersoldbean

barkersoldbean

Posts: 22

Thanks for the clarification - I had actually noted your earlier comments (which were eminently logical), but was confused as this simple explanation appeared to be at odds with your literature (Quad 44 revision version 2.5) where you display a picture of the tone control board (serial number >23000) with the IC at the edge of the board next to the volume control marked as at IC 701, not IC 700?

Before I start trying to fault find - I need to know which is correct?

Tony

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14-Mar-2019 02:26 AM

EJP

EJP

Posts: 1559

I have that page printed out with IC701 crossed out and IC700 written in by me. I believe I am correct in this, not the page.

But it's easy enough to test. Just remove the leftmost op-amp and see which channel you lose. If it was left, it was IC700, otherwise IC701. Let us know which it was so I can correct the above if necessary.

EJP
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14-Mar-2019 04:34 PM

barkersoldbean

barkersoldbean

Posts: 22

Thanks - in the end I remembered a piece of advice from you many years ago - on a 303 upgrade that went a bit awry - check the pins, check for dry joints, check for tracks broken........repeat.....

After checking for the 5th time with a high mag light and wiggling the IC pins - I found a dry joint on IC4 and hey presto - a bit of solder and all is perfect. Both channels alive and well.

After then sorting out the caps and ICs on the main/psu board and the caps on the Disc board - the difference is just amazing - lots of sound reappeared that was lost before!

Sorry for being a pain over the constant questioning - but it just proves that a massive upgrade can be done for a few €'s with only a modicum of ability!

Thanks for enabling people to keep their pride and joy alive!

Tony


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