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Sick Sansui AU-717

72.229.31.195
Posted on November 4, 2009 at 11:14:26
JGarvey
I am hoping to get some good advice on how to repair my Sansui AU-717.

I notice yesterday that the B Channel is very weak about a quarter of the volume strength of the A Channel.

Is this something I can repair myself or do I need to get it serviced.

Thanks, Hope Someone Can Help,

Joe

RE: Sick Sansui AU-717, posted on November 12, 2009 at 10:01:44
big joejoe
 i have the same amp,and its well worth fixing.BUT i had a problem like yours and it turned out to be a dirty coupling? switch. it is located on the rear of the amp and allows you to split the amp power from the pre amp control. it should be blocked with a clear plastic "lock", remove the lock and move the switch back and forth a few times. to really make sure you get it clean, remove the cover(after you have unplugged it from power) and you should be able to better see and apply a SMALL amount of cleaner to the switch. move the switch a few more times,put the amp back together, making sure the switch is in the proper position and plug it back in and you just may have saved a trip and a few bucks. best of luck.

RE: Sick Sansui AU-717, posted on November 12, 2009 at 11:04:55
JGarvey
 Thanks for all the good advice.

When I approach my amp after not turning in on for a couple of days both channels were strong?

Maybe it was really sick?

Joe

RE: Sick Sansui AU-717, posted on November 4, 2009 at 13:29:46
FenderLover
Audiophile

Posts: 3308
Joined: July 31, 2007
Contributor
  Since: May 17, 2009
 I suppose you've check all fuses. Are the filter caps original? If so, maybe best to have a tech go through the amp.

RE: Sick Sansui AU-717, posted on November 4, 2009 at 18:03:20
djk
Manufacturer

Posts: 3886
Joined: June 17, 2000
 It is probably NOT the filter caps.

Clean all the switches and controls, especially the tone turnover switches (if applicable).

I had a DB9090 and that was usually the problem.

The other problem is the smaller caps drying out, especially the interstage coupling caps, and the cap in the feedback loop of the main power amplifier.

If would help to have the schematic.

I sure hope the sick heals quickly..., posted on November 5, 2009 at 15:51:48
Interstage Tranny
Audiophile

Posts: 1403
Location: Eastern
Joined: October 4, 2006
 ...very decent amp. Remember, these old items have gained oxidation, which means bad switches and connections can yield resistive circuitry, losing gain and quality sonics. Then, the coupling caps are getting old, absorbing moisture to change cap value, or simply drying out reducing cap value drastically, changing response accordingly. Some of those now 20 plus year old electrolytics are used for coupling between stages. No doubt some have changed value or are even going open. If one channel is still good, the power supply electros are probably still okay. However, a cap meter is in order for troubleshooting.

One of my most trusty tools is an old tubed Signal Tracer. For finding opens and weak signal offenders, sig tracers are very handy...

Cockroaches ?, posted on November 6, 2009 at 02:14:18
djk
Manufacturer

Posts: 3886
Joined: June 17, 2000

I find an inexpensive cap meter is not of much use.

Most of these caps fail due to high ESR, not the value change, and you generally have to pull them out of the circuit to test.

The easiest way to check is to put some test prods on a 100µF 100V NP electrolytic and just parallel the suspect cap (be sure and discharge the cap after each test).

In general though, bad caps are like cockroaches, ya gotta get 'em all.

Bug collector R U ?, posted on November 7, 2009 at 16:38:46
Interstage Tranny
Audiophile

Posts: 1403
Location: Eastern
Joined: October 4, 2006
 When you speak of caps leaking DC to the next stage, yes they need replacement.

However, there are some fine sounding classic caps still in use. Your ESR test may weed out future culprits, too, but classic vintage stuff, when working and sounding fine, do not NEED to be replaced. I disagree about replacing them all. If we're talking about a working unit, functional, without fuzzy, grainy sound, why replace the originals if they were of high quality ? Find the fuzzy inducing culprits and replace what you must. Then, match what you must. Then, listen again, and enjoy, as soon as possible...

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