AU 7900 No sound, no 'click'

[homeydcat]

I'm a newbie so be patient.

I recently found an AU 7900 and 4 speakers listed under a curb alert on CL. I was astounded to find this amp for free. The lister said he thought it worked last time he used it 2 years ago. I couldn't wait to hear it. But I patiently took the amp apart and thoroughly cleaned it inside and out. I removed the faceplate and cleaned all switches and pots with a good non-residue contact cleaner. After polishing and even waxing (I know) the faceplate I put it all back together. I then connected a CD player and a pair of speakers to test. Turned the unit on, power light lit .... nothing. No 'click' from the amp and no output. Tried other RCA jack inputs, turned and/or flipped all knobs .... still nothing. When I had it apart I carefully inspected for blown caps, leaking caps, blown fuses, etc. There was no discoloration, smell or anything I could see out of the ordinary.

My question is now that I've looked for the obvious, what is my next step short of giving to someone else to fix? The lister is long gone so I can't ask him anything. I have years of experience soldering but my experience ends there. I have no formal background in electronics and don't own a scope. I'm sure I have a meter or 2 around somewhere and I could follow someone else's instructions in looking for the problem. Any help would be appreciated. Thanks.

P.S. I've included some pics. There is one area on the back that shows some moisture contact in the past. This seems its only flaw.

 

[Dswankey]

First and foremost Awesome Find!!!!, I know little about repairs but I'm sure someone will be by shortly to share their knowledge.

 

[ManyMoonsAudio]

Get a service manual... Check the DC voltage at R73 and R74 next to the relay. Should be close to 0mv-dc. This amp also has a few fuse resistors in it.

Check the FAQ sticky at the top of the forum to find out what they are and what they look like....

They are R31, R32, R41, and R42 (220ohm). Replace them with metal film 1/4 watt.

 

[nosirrah]

Doesn't that have a connect/ seperated switch on the back?
If so I bet that's it....

 

[homeydcat]

Doesn't that have a connect/ seperated switch on the back?
If so I bet that's it....

You think the switch is just dirty or in the wrong position?

 

[homeydcat]

Get a service manual... Check the DC voltage at R73 and R74 next to the relay. Should be close to 0mv-dc. This amp also has a few fuse resistors in it.

Check the FAQ sticky at the top of the forum to find out what they are and what they look like....

They are R31, R32, R41, and R42 (220ohm). Replace them with metal film 1/4 watt.

Thank you for your help. Unfortunately, much was over my head.:sigh:
1. The only manual I was able to find is a 4 page PDF. It seems to be incomplete.
2. Again, I'm brand new. My 1st post ever. Anyone have pictures showing where ManyMoons is talking about?
3. I'll look for the sticky, thanks.
4. Any suggestions where to obtain these 1/4 watt metal film replacements?
Thanks again.

 

[ManyMoonsAudio]

If you look at the board on the bottom, I gave you the part designations. They should be printed on the circuit board. Read my previous post again...

Check the DC at the big resistors next to the relay, with one meter lead to chassis...

Buy the resistors at Mouser, or you may get lucky at Radio Shack...

Casey, he did say "No click" from the amp, so the speaker relay is not engaging..

Free copy of the service manual at Hifiengine. You have to register.

 

[Hyperion]

You think the switch is just dirty or in the wrong position?

I suggest "just dirty" so that even in the correct position the switch passes no signal.

They are R31, R32, R41, and R42 (220ohm). Replace them with metal film 1/4 watt.

Like This

 

[dr*audio]

If it sat for years and used to work, it could be those resistors, or the corrosive glue that holds the large electrolytic caps down could have eaten through some component leads. Look for brown goo at the bottom of large caps. If any of the leads or jumpers it touches are green, remove the glue with a dental pick and check that the leads are not corroded through.

 

[ossodiseppia]

Doesn't that have a connect/ seperated switch on the back?
If so I bet that's it....

In the picture he's posted of the back of the unit, it looks like the switch is set to separated.

 

[dr*audio]

In the picture he's posted of the back of the unit, it looks like the switch is set to separated.

The relay doesn't click.
The relay doesn't click.
"Pay, I say, pay attention, son. I ain't a-talkin' just to hear my head roar!" - Foghorn Leghorn

That means you will get no sound no matter the position of the switch. There is a problem in the output stage. He needs to fix that, THEN set the switch to "connected."

 

[ManyMoonsAudio]

the relay doesn't click.
The relay doesn't click.
"pay, i say, pay attention, son. I ain't a-talkin' just to hear my head roar!" - foghorn leghorn

that means you will get no sound no matter the position of the switch. There is a problem in the output stage. He needs to fix that, then set the switch to "connected."

lol!

 

[kevzep]

Yes yes, we know the relay doesnt click Warren......

But there is most likely several things going on here which are contributing....I dont think Brian quite deserved Foghorn Leghorn, although I thought that comment was really funny.....

1, the switch is set to separated
2, the relay doesnt click
3, there are probably fusible resistors which need replacing

and I'm sure there are more things to add to the list......like all switches and pots need cleaning for example.

 

[Zekeman]

I just fixed one last week that had the same problem....I rebuilt the power supply board which had open fuse resistors.

I can not belive you got that beut for FREE!!! Got to be a score of a lifetime. IMHO this is now my fav Sansui integrated (and I've heard lots).

Good for you...fix it and keep it!

 

[nosirrah]

I didn't hear the relay click either.....silly chicken.

 

[EMark]

check this too...

I had a similar problem with my AU-7900. After checking everything the other postings suggested and it still is not clicking in, then have a look at TR 603. It is right next to the relay.

 

[homeydcat]

Thanks for all your suggestions. Tax weekend kept me from responding.:tears:

Pots and switches have already been de-oxed. I took apart the back of the unit and double-checked the switches on the back. Cleaned again. Still no click as was told would happen by Foghorn Leghorn. I will check and change out the appropriate resistors. I have joined Hifiengine and downloaded the complete manual. Will post when I do the work and get some (hopefully positive) results.

Thanks again.:thmbsp:

PS I've attached more photos of the interior.

 

[crankdoctor]

What are the 4 fuses on bottom for? I have one that worked 4 years ago. When i hooked it up about 3 weeks ago i had no power.

 

[Hyperion]

What are the 4 fuses on bottom for? I have one that worked 4 years ago. When i hooked it up about 3 weeks ago i had no power.

Please start your own thread for this issue.

 

[Karl Webb]

Just joined. Hi everyone.

I saw one of these on CL with matching tuner. Same issue. Read all the above and we'll see if we can get the old girl to kick over. Thanks to everyone for posting here oh-so-long-ago.

I bought it because I remember the sound of dad's QRX 6500 while listening to music through the computer. I missed REAL SOUND QUALITY. Wish me and my best friend luck as we tear into her.

Homeydcat, did you ever get it working?