'my turn for a CJ Preamp "logic problem"

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Ray
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'my turn for a CJ Preamp "logic problem"

Post by Ray »

I guess it's my turn to be in the barrel....

All of a sudden, the "Standby" LED on my preamp is intermittent. (GAT)

The preamp goes into Standby fine, and normally this is confirmed by the illumination of the "Standby" LED.

Functionally, everything appears normal, it is going into Standby, and it comes out of Standby fine...it's just that intermittently I have no Standby indicator.

It's a minor issue to be sure, but, I'd sure like to have it work 100%.

I of course removed power, and reapplied, did a few tests etc. it seems to more often happen if the preamp is on for a few hours. maybe heat related..?
I popped the top and had a look at the "logic" board, nothing obvious of course, although the soldering quality is what I'd rate as fair at best. so it might be a cold solder joint.
Near as I can tell with no schematic, the status LED in question is driven by a 74C595.
I'm tempted to pull the board entirely and do a bit of solder re-touching but figured I'd wait a bit. I did send an email note to CJ for inquiry, hopefully more info back this week.

Question: It seems schematics for "modern" CJ gear do not exist. But, since it appears the identical logic board is and has been used for many years now by CJ, does anyone have one or know of a way of acquiring a schematic of the board? I assume not, but thought I'd ask just the same. :D
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Re: 'my turn for a CJ Preamp "logic problem"

Post by admin »

Hi Ray. Sorry to hear about the problem. Just so I understand, this is basically a cosmetic issue with the standby light, and not actual function, correct? If so, I would try taking the top off of the unit, putting it in standby, and then try to put gentle pressure on the internal components with a non-conductive item (such as an eraser of a pencil). By flexing the contact joints a bit you may be able to find a simple contact point that has weakened. If putting slight pressure on a component makes the light go off and on, then you most likely need to fix the contacts. Let us know how it goes.
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Main stereo: ART Amplifier and ET7s2. 2nd stereo: PV-14L and MV-55. Previously Owned: PF2 preamp, Evolution 2000 Amp, PV-12AL preamp, D/A-2b Vacuum-Tube Digital Processor.
Ray
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Re: 'my turn for a CJ Preamp "logic problem"

Post by Ray »

Oh yea, I removed the top, actually removed the board itself and had a look.
it doesn't appear to be a mechanical intermittent, but then again a cold solder joint would classify as such.

purely a cosmetic issue it appears. the LED actually does illuminate for just a brief second when standby is selected.
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Magnepan 20.7
Conrad Johnson ART 300
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Re: 'my turn for a CJ Preamp "logic problem"

Post by admin »

I'm not familiar with the inside of the GAT, but could you trace the leads of the LED back and perhaps put a voltmeter on the contacts to see if the voltage to have it on is lost somewhere along the path or not coming out of the source control chip.
-admin
Home Theater in Member Gallery
Main stereo: ART Amplifier and ET7s2. 2nd stereo: PV-14L and MV-55. Previously Owned: PF2 preamp, Evolution 2000 Amp, PV-12AL preamp, D/A-2b Vacuum-Tube Digital Processor.
Ray
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Re: 'my turn for a CJ Preamp "logic problem"

Post by Ray »

If I could scare up a schematic...it would sure help with troubleshooting at component level.

in the meantime I may ask CJ if they'll "loan" me a control board to try.
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Magnepan 20.7
Conrad Johnson ART 300
Conrad Johnson GAT V2
Meitner MA 1 V2
Custom Server running MC 23
Dual Synology 1512+ 12 TB total storage
Ray
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Re: 'my turn for a CJ Preamp "logic problem"

Post by Ray »

Update:
Spoke with CJ Service, once again a pleasant experience. Instead of "We've never had anyone ever report such an issue", I was told that in fact over the years they have heard of and seen a few instances. Literally being so few and far between as virtually impossible to troubleshoot. On top of that, they are swapping out the logic board in my GAT.

I laughed a bit as the concern was that they would never consider sending a board out to a user, so it took a little bit of convincing on my part, but just a little.
I was all prepared with " I've been working in electronics since before you were born sunny-boy", but I didn't have to pull out that secret weapon. :)

In examining the board, I do have at least one -stab-in-the-dark idea of what might be happening. If it happens again with the new control board I may make a little modification and see what happens. The problem being this issue can happen a few times, then go away for a month or two or 20. OBTW, it's hell being without music if even for a few days.....I guess the desktop computer music player will have to do for now.
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Magnepan 20.7
Conrad Johnson ART 300
Conrad Johnson GAT V2
Meitner MA 1 V2
Custom Server running MC 23
Dual Synology 1512+ 12 TB total storage
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