Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Right channel distortion on vintage fisher rs-2010

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
 

suzook

New Member
Hopefully this helps! That's directly from the positive output of l, and r channel
 

Attachments

  • 20220806_121621.jpg
    20220806_121621.jpg
    1.6 MB · Views: 65

suzook

New Member
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
 

suzook

New Member
The amp schematic gives voltages at various points - are they correct on both channels?

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?
 

Nigel Goodwin

Super Moderator
Most Helpful Member
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
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.
 

suzook

New Member
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.
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:

suzook

New Member
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
    20220806_162323.jpg
    1 MB · Views: 66
Last edited:

Nigel Goodwin

Super Moderator
Most Helpful Member
Welp, I got the same signal on the power board. So it's definitely something there. Hmmm
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.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
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.
The mute relays are part of the power board.


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?
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..

Amp_STK_highlighted.jpg
 

suzook

New Member
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.
1000khz signal.
 

Latest threads

Top