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Old 28th May 2008, 02:14 PM   #1
nukei&c is offline nukei&c  United States
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Default Sansui 9090 DB help


I am a newbie to the forum and I am looking for advice with a problem with my 9090.
Problem:
After a few minutes of play, the right channel drops out. After a long while, it will kick back in. I believe that a power transistor is overheating.
Questions:
1. Could someone please tell me if I am on the right track about the cause?
2. What are the correct, currently available, parts needed for repair and...
3. Should I also do the same to the left channel while I'm inside the unit?

Thanks to all for any help and advice.
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Old 28th May 2008, 03:14 PM   #2
Corax is offline Corax  Germany
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Hi nukei&c,

first of all you better download the service manual for your 9090 (i.e. from http://www.eserviceinfo.com/download...sui_9090.html, it's a multipart download - which consists of only two <*.RAR> archive files).

According to your fault description it looks really like a thermal fault, but where it's located could be just a guess and without measuring certain things you won't find it anyway.

Since the protection circuit, and therefore the output relay, cuts off both channels at the same time it can't be any fault condition of the driver amp itself - or does any protection indicator light up and the relay just fails to disconnect one channel?

If you want you can go step by step through the troubleshooting chart (chapter 5) and check everything mentioned. A good point to start, if on the dropped channel appears no noise or anything else, is to check all power supply values if they're in range.

If all power levels are OK check the signal path either from the beginning (where it comes from, i.e. tuner section) or from the end point (where it will leave the receiver to your power amp). Go through all signal stages in a straight sequence and whenever the signal just appears or disappears (depending on the before mentioned direction) the signal is lost in the stage between the last and the previous stage.

Whatever you figure out let us/me know and we're pleased to help you when it comes to the point to trace the fault down to the possibly defective components (i.e. resistors, capacitors, transistors, ...).
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Old 29th May 2008, 10:28 PM   #3
nukei&c is offline nukei&c  United States
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Thanks Corax,

I will get the service manual and start chasing the ghosts.

I just fired the unit up and after adjusting the Balance control to full right, I have no sound. The Protection LED is off. Does this sound like a totally different problem from my orginal post?


thanks for your help,

Nuke
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Old 30th May 2008, 01:09 AM   #4
quoydoy is offline quoydoy  United States
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For what its worth, I got a 9090 db from the dump where I work.

When I turned it on, the left channel was intermittant, sometimes distorted. It has a mono button, and both channels would play.

I cleaned all of the pots accept for the dolby controls on the front, why I didn't clean them, I couldn 't say. Now, most of the time it works fine, and when it doesn't I can touch the dolby selector, and toggle the left channel back on wiggling the dolby control.

I'm going to reclean everything with deoxit.

Given how old these amps are, perhaps cleaning the pots might be a wise first step.

Best wishes,

Brian
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Old 30th May 2008, 01:35 AM   #5
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I agree.
Dirty pots/switches can cause all sorts of weird issues.
Cleaning them up is a good first-round step. Along with; visual inspection,checking fuses,etc. for any 'tell-tale" signs of trouble. (atleast with a piece thats "new" and "unknown" to me.)
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Old 30th May 2008, 02:47 AM   #6
Leolabs is offline Leolabs  Malaysia
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Also check for bad solder joints.
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Old 30th May 2008, 02:15 PM   #7
nukei&c is offline nukei&c  United States
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Thanks for the replies. I will give it a good cleaning as suggested first. Will let y'all know what happens.

Thanks again,
Nuke
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Old 28th July 2008, 02:02 AM   #8
lineup is offline lineup  Sweden
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And what has happend, nukei&c
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