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Old 24th February 2007, 06:31 PM   #1
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Default Schematic and help with Threshold SA/4

Howdy!

First, let me say how refreshing it is to have the Man himself among us... we're not worthy! Totally cool.

I've got an SA/4 that I obtained broken (paid almost nothing, too!). It's in perfect cosmetic shape, and I'd like to try using this amp for awhile.

Initially, it was blowing fuses on one side upon power-up. I discovered a single bad output device on the channel, and changed it. I also checked every other device and resistor on the side. Changing that device solved the problem at idle.

Unfortunately, there is still trouble. At about 1 watt of output on the defective channel, current draw from the mains moves massively up and distortion goes way up, as well. I have been all over the driver board for that channel and measured every passive and every semi (de-soldered), and can't find anything out of sorts. And I'm out of ideas, particularly because I don't have a schematic.

Can anyone help with one? Does anyone have an idea of what this might be?

Appreciate the help, and very glad to be here!

-Pacific
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Old 25th February 2007, 07:02 PM   #2
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I'm totally unfamiliar with that amp but suppose the zobel network (if any) would be shorted to ground?
Oh...and Jacco is a fairly nice guy.

/Hugo
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Old 25th February 2007, 07:41 PM   #3
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Hugo,

i bet you're very good at charming les merveilleuse femmes as well.

Pacific friend, send me an email for the SA/4e schematic, courtesy of the one and only who ocassionally does a sleazeball like me a big favor.
Paid almost nothing ? Oh dear, i'm fainting again.

His Holiness himself may be arriving shortly on this stage, has a lot more hair than Tenzin Gyatso, let me just cough 1-2-3-testing in the mic.
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Old 25th February 2007, 07:49 PM   #4
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Me?…To..ta..lly innocent. Although I wouldn’t mind the drawing.
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Old 27th February 2007, 03:31 PM   #5
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Hi, guys:

Sorry to not check in earlier- shortly after that first post, my main box (sigh- this is the one I do all my audio remastering and video projects on) crashed harder than Humpty Dumpty on crack. Totally hosed Windows, cross-links on data files (on ANOTHER, different partition!), the works.

I am only now coming back to life... Still can't get the install of 2K to work right (may have to give up). Since my practice is always to stay one generation of OSes behind, I guess this is my calling to get on with the business of living with and trying to like XP.

Happily, almost all the data lost was either backed up, or very recent. About the only thing I haven't been able to recover is some recent cover art that I should be able to recreate without too much trouble.

Lesson: Regular back ups. I had gotten lazy and that's a fatal error when things go bad.

Anyway, thanks for the reply! Jacco and Hugo, nice to meet you both. Jacco, look for a private from me for a mailng addy, your generous offer is very much appreciated.

Please let me make one in return:

Along with many hats before then, I was the undertaker for Pacific Stereo when it died in 1986. I eventually ended up with 18,000 paper service manuals, mountains of microfiche, and boxes and boxes of original parts, including semis, lots of them. I've even got new optics for a CDP-101. Need factory heads for the original Advent cassette deck? Got 'em... You get the idea.

The S/M collection is supplemented by stuff from The Federated Group and other service organizations, and goes to about 1996 for many, many brands.

If anyone here needs a part, a schematic, or anything else along those lines, please PM me and I'll get you fixed up.

Jacco, watch your message box!

-Pacific
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Old 27th February 2007, 03:31 PM   #6
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Ugh. It would appear that I am still under moderation, so I can't use the email feature of the forum. As soon as I am out of Forum Purgatory <grin>, I'll contact you, Jacco.

-Pacific
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Old 27th February 2007, 03:47 PM   #7
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Let's do better, i'll fill your mailbox instead if you put a time window on your email button to let me in briefly.
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Old 27th February 2007, 06:00 PM   #8
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You might want to take a look at the thread "Repair question re:
threshold 400a" which follows the progress of a major repair
effort.

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Old 27th February 2007, 06:15 PM   #9
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I don't have SA4e schematics, but I do have the SA12e
which is very similar. I have uploaded the 15 pages of the service
manual to www.passlabs.com/np

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Old 28th February 2007, 03:22 PM   #10
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Nelson, nice to meet you, and thank you! I will grab that manual, and check out the 400a repair thread as well.

-Pacific
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