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Sansui AU 5900 Help

richersounds

richersounds

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Hi. Long time since my last post.
Picked up an sansui au 5900 for 150$
Has some static on one channel. isolated the problem to the volume control, will spray with deoxit.
Can someone give me an idea of the best area/direction to spray the deoxit into so I am definitely getting good coverage of the contacts?

also looking at the board I noticed some heat damage?

can someone also tell me why this part is getting so hot and what it’s purpose is on the board?
Thanks in advance!36E38968-76F5-45CB-A315-506643DD59B3.jpeg
 
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Its more likely to be glue than heat damage.

You want to download the service manual at hifiengine.com and start getting familiar with how these look:

file:///C:/Users/barrs/OneDrive%20-%20AgResearch/Downloads/hfe_sansui_au-5900_6900_7900_service.pdf

In order to diagnose your crackling issue you need to think about:

Does the noise start straight after power up, or after a while (ie: when things warm up),
Does the noise occur on all inputs?

You have already stated that the noise is only in one channel, and thats a good start.

Ironically - the component you have pictured is potentially a suspect one - the schematic confirms this is a VD1212 diode, these need to be replaced, so do this, by using 2 x IN4148 diodes in series. These are on the power amplifier board F2596.

The schematic also confirms that "IC 01" is a 2SA798 - double transistor. You need to replace these also - with 2 x 2SA992 transistors that are matched for hfe.

If these things sound like they may be tricky for you to do, I'd recommend you take this amp to a tech.

If however you think you can do these things yourself, ask here for more details, and we can take you thru the required steps.

Capture.PNG
 
This is a great help thanks a lot. I will start with deoxit and see if the issue resolves.

I am actually interested in learning to do a full recap so I will keep you posted!

thanks!

so the actual issue is no sound on one channel on power up. Until you play with volume control and it cuts back in. So I was thinking carbon buildup in the volume pot hence the deoxit.
To my knowledge this amp sat for years unused. Very nice condition. Only issues were the bad channel and power light would not come on which I already fixed.
 
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In the first image, R12 is a 3.9K ohm 1/2W (bottom at left, next to C12) and appears to be a fusistor (greenish colour). it's connected to the VD1212 diode. You could check it, just in case.
R11 (same fusistor) is in the schematic, left channel. Could also be checked.
 
richersounds said:
Until you play with volume control and it cuts back in
Click to expand...
So do you mean if you fiddle with the volume a little bit in either direction, the sound comes back? If so - yea, clean the volume pot contacts.

Or do you mean if you turn the unit quite loudly, then the channel kicks back in - if this is the case, the speaker protect relay could be your issue - worn contacts
 
slimecity said:
So do you mean if you fiddle with the volume a little bit in either direction, the sound comes back? If so - yea, clean the volume pot contacts.

Or do you mean if you turn the unit quite loudly, then the channel kicks back in - if this is the case, the speaker protect relay could be your issue - worn contacts
Click to expand...

Ah yes! It appears to be when turned up quite loudly it kicks back in. Where is the speaker relay located?
 
richersounds said:
Ah yes! It appears to be when turned up quite loudly it kicks back in. Where is the speaker relay located?
Click to expand...

OK thats the first thing Id look at in that case - I dont have the schematic or manual in front of me at the mo but it will be in a clear plastic case, its the thing that goes "click" a few seconds after turning it on. You would be best to replace this. The new one needs to have the same coil voltage and pin configuration.
 
Update. Oddly enough after cleaning a couple of boards with isopropyl alcohol and the glue/heat damage shown in the photo, the issue has been resolved. Both channels work fine now. There is no pop and crackle on the volume control. A bit of static on tone control switch remains.

however upon listening the same channel appears to have a minuscule amount of less power. Just about audible if you listen carefully.

I will go into speaker selector and clean the contacts and the rest of the amp with deoxit and see how it sounds after.
 
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