• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

9090db floating resistors???

xratedpez

xratedpez

Super Member
Anybody seen anything like this before? Took the bottom off my newly acquired 9090db, doesn't appear to ever have been touched. However, these 2 large resistors are just floating in here, melted to a few wires... Never soldered. Not connected. Weird as hell!



45cd17f9-bdfb-ba30.jpg
 
Register to hide this ad
When I took them out, I noticed a small cap w/ a split top cover (you can see the greenie) and a wirewound resistor whose lead was unattached as well! How is this thing actually working and producing good sound?


aee24180-c25a-e50f.jpg
 
My guess is the resisters are in the headphone circuit, and got overheated with high volume operation\shorted head phone line\plug.

Mark T.
 
All those green film caps need to be replaced, and the resistors carefully checked, and reinstalled.
 
Last edited:
I'd say that is another of Sansui's famous SM errors.

In any case, the schematic calls them out as 4.7 ohm 3W. I think they may in fact be 10 ohm 3W (should be able to measure the ones in place and determine what they are). Still, they are part of the Boucherot cell (some call it a Zobel filter) at the power amplifier output, designed to provide a more substantial load to the amplifier at high frequencies to promote stability. The blown film caps (and I see a lot of of these little greenie caps dead in the Zobel filter of Sansui amps) indicate that the amp very likely was suffering from oscillation problems and the blown caps were shorting the output to ground through these low value resistors.

The film cap needs to be replaced with a good quality non-inductive metal polyester rated for 250 to 400V, and I'd replace the resistors as well.
 
One resistor isn't measurable.. Both have substantial cracks. The other measure 7.5 ohms. The brown bands didn't discolor consistently, but can see they've got to be brown.

These were resistors r13 and r14 in the board. Will replace with 3-watters to be safe.

Also, what's the best way to get at this board to solder?
 
they must have been connected to get hot and melt the wire .it is a little odd how the lifted up like a burning match would do though
 
Take the tuner assembly out. Pull the faceplate off. 8 screws on top. Un-plug all the connectors and there is also a couple hiding underneath once you start lifting it.

You will then see the protect board.
 
Oscillation really shouldn't be there if the zobel networks are functioning as designed. It would typically show up as a fuzzy trace or ballooning near signal peaks on a scope. If present, I would tend to look for bad transistor subs first.
 
Yikes. These greenies are mylar? Is polyester film a suitable replacement?

They are marked 104K 50V (i think), the SM says 0.1 uF. Wondering whether to trust it or not at this point!
 
0.1µf is the proper cap value. The resistors must be 4.7 ohm if one is open and the other measures 7.5. Since resistor value ain't never going down, it must have began life as a 4.7 ohm job and not 10 ohm.
 
hard life that one had....

The two resistors at the top of your pic next to the relay look,,, uh.. compromised, too.
 
You must log in or register to reply here.
Back
Top Bottom