Right channel distortion on vintage fisher rs-2010

Status
Not open for further replies.
S

suzook

New Member
I have a vintage fisher rs-2010 that uses the "famous" stk packs. I get sound on both channels, but the rt channel has some distortion. My dc offset on good channel is 7mv, and the distorted channel is 32mv. That shouldn't cause my issues. Any idea where to start? Thanks
 
Sort by date Sort by votes
I take it the top one is the good channel?, as the bottom seems to have some visible 'missing bits' - what range is the scope set to? (V/cm).
 
Upvote 0 Downvote
Yes, that one is clean, the other obviously looks bad. Scope at 2 on 10x probe. No idea where to go from here. Lol. Trace it back?? If so, I don't know where to start
 
Upvote 0 Downvote
So I measured voltages on amp board on all transistors. Most were within 10%. Some though were off more. My issue though is both sides of the board were identically off, so I would expect distortion on both. Maybe my problem is before the amp board?
 
Upvote 0 Downvote
suzook said:
Yes, that one is clean, the other obviously looks bad. Scope at 2 on 10x probe. No idea where to go from here. Lol. Trace it back?? If so, I don't know where to start
Click to expand...
That's not very clear - do you mean the scope is set to 2V/cm, then a x10, so it's 20V/cm? - in which case that's 40V p-p, which is about 25W.

Do the same test with the volume turned down, so you've only got 1V or 2 V p-p.
 
Upvote 0 Downvote
Nigel Goodwin said:
That's not very clear - do you mean the scope is set to 2V/cm, then a x10, so it's 20V/cm? - in which case that's 40V p-p, which is about 25W.

Do the same test with the volume turned down, so you've only got 1V or 2 V p-p.
Click to expand...
Yes, thats exactly what it was. Will redo test after my beer and swim in the pool! 90 outside right now!
Sorry, still learning how to use a scope. Appreciate all your help.
 
Last edited:
Upvote 0 Downvote
Ok, here is 1v, power at 50%.. Can I check before, and after the speaker relay? I'm thinking bad relay
 

Attachments

  • 20220806_162323.jpg
    1 MB · Views: 346
Last edited:
Upvote 0 Downvote
suzook said:
Welp, I got the same signal on the power board. So it's definitely something there. Hmmm
Click to expand...
What frequency are you putting in?, and it's still unclear what the scope is set to, as you can't see the line on the knob in the picture.

Set the gain control to 50mV, set the probe to x10, and make sure the Red 'Cal' control is fully clockwise (it should almost always be there, and may have a click position), this gives 500mV per division on the scope. Then adjust the volume for 2 squares on the scope, giving 1V p-p.

The chances of a relay causing distortion is extremely low, but you can certainly check both sides of the contacts if you wish.

If you're getting the same signal on the power board?, where on the power board? - as it's only on one channel it can't really be on the power board.
 
Upvote 0 Downvote
Nigel Goodwin said:
If you're getting the same signal on the power board?, where on the power board? - as it's only on one channel it can't really be on the power board.
Click to expand...
The mute relays are part of the power board.


suzook said:
So I measured voltages on amp board on all transistors. Most were within 10%. Some though were off more. My issue though is both sides of the board were identically off, so I would expect distortion on both. Maybe my problem is before the amp board?
Click to expand...
Check the collectors of the upper and lower transistors that drive the STK module with the scope, on both channels?

If the signals there are identical on both channels, the fault can only really be in the STK module, something failed within its bias control presumably..

 
Upvote 0 Downvote
1000khz signal.
 
Upvote 0 Downvote
Status
Not open for further replies.

Similar threads

S
  • Question
Korg piano fault-all lights on, unresponsive
Replies
0
Views
158
Snailer99
S
E
  • Question
Sunny TV Stuck on Boot Screen
Replies
1
Views
2K
riccardo
Reviving vintage Realistic DX-302.
2
Replies
23
Views
4K
shokjok
S
P
membrane touch pad not working on 1 function
Replies
13
Views
3K
starLED
R
  • Question
Vertical Lines on Half of Display
Replies
4
Views
3K
rfxcasey
R
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…