SX 1050 tone switch problems

[Stereoboy70]

Hello everyone, I’ve got a question about an SX 5580(1050) tone board issue. This receiver has been restored and recapped Thoroughly cleaned and tested but the issue is with the tone switch. When off the receiver sounds great. No issues. When the tone switch is turned on , the R channel volume is super loud and the left channel drops a lot. I’ve checked and double checked the caps and transistors on this board. The switch was removed and cleaned with Deoxit again. Checked all of the resistors and cap orientation. Good. Wiring to other boards is good. Checked solder traces. Good. Checked flat amp
Board for any baxkward caps etc…… good. Question is why does the volume increase when the tone board is engaged? And only on the r channel?? This receiver plays and sounds fantastic until you introduce the tone board. I feel the problem exists there but I can’t seem to find it. Thanks n advance

 

[mrk229]

Do you have any way to signal trace a tone through the board to find out where the problem is? You have a good channel to compare too.

 

[kwayde]

If it was working good beforehand it's something you changed. Double check cap values and placement. It's easy to put them in the wrong place. Been there, done that.
Triple check xstr pinouts.

 

[Stereoboy70]

Do you have any way to signal trace a tone through the board to find out where the problem is? You have a good channel to compare too.

Yes. I can trace the signal. Both channels are fine until I introduce the tone board then the right channel volume gets super loud and the left channel drops off so you can barely hear it. I’ve double checked the caps etc…. It’s definitely something on that board though. I’ll take a look this week
Thanks

 

[mrk229]

Yes. I can trace the signal. Both channels are fine until I introduce the tone board then the right channel volume gets super loud and the left channel drops off so you can barely hear it. I’ve double checked the caps etc…. It’s definitely something on that board though. I’ll take a look this week
Thanks

What I meant was signal trace through the tone board circuit itself stage by stage from input to output. See example below.

 

[zebulon1]

Concentrate on the side that is weak. Probably a coupling cap in backwards. Then look at the other channel if it hasn’t started to behave.
Even a filter cap backwards could draw down the voltage on the weak channel and effect the other channel.
Mostly a backwards transistor allowing stray voltage, will cause a pop when selecting the tone on.
Poor connections. Solder bridge. Torn trace, among other issues.
I would guess its operator error. It seems more like an abnormal failure. A natural failure would not cause the observed fault.

 

[Stereoboy70]

I will trace the signal through the tone amp this week. I have gone over the board about a dozen times and all the caps are correct in value and placement. The transistors were replaced with c1845’s. They are in the correct orientation. The pots are correct ohms and the selector switch is working correctly. I will dig some more and post the results. Thanks for the help MRK229 and Zebulon1.

 

[Brian1970]

The tone defeat switch is pretty impossible to clean without disassembling it. Trying to spray deoxit in it is unlikely to work well enough in my opinion. Trace the signal to verify where you're losing it but if it's at that switch, you probably need to take it apart and clean it well.

 

[Stereoboy70]

I will disassemble it and clean it. I noticed when I first flipped the switch I got a super loud buzz/hum through the speakers. Speakers are fine. I had the board out of the unit when it did this and after putting it back the noise went away. Now just the loud R channel and low left channel. Thanks again. Love your user name. I'm also Bryan and my DOB is 1970.

 

[Stereoboy70]

I triple checked all components. All ok. I disassembled the tone selector switch and cleaned the contacts with a very small file. I also cleaned the small copper sliders that connect the main contacts. Put it back together and it sounds great. No buzz. No pop. No hum. Contacts were very corroded. Brian1970 is correct. You must disassemble the tone defeat switch to clean it properly. Thanks again to everyone who chimed in with suggestions.

 

[Brian1970]

I triple checked all components. All ok. I disassembled the tone selector switch and cleaned the contacts with a very small file. I also cleaned the small copper sliders that connect the main contacts. Put it back together and it sounds great. No buzz. No pop. No hum. Contacts were very corroded. Brian1970 is correct. You must disassemble the tone defeat switch to clean it properly. Thanks again to everyone who chimed in with suggestions.

Glad it's working now. Something to be aware of for future projects, I'm not positive about the contacts in those switches but I suspect they're silver plated copper. A file is pretty aggressive and may remove all the plating. What I've done in the past is use a mild silver polish and rub them gently with a q-tip and try not to remove too much of that silver plating. For the sliders I use a piece of fairly stiff paper that'll slide inside them without expanding them outward. Then rinse everything well with isopropyl alcohol or maybe give them a few minutes in an ultrasonic cleaner. Contact resistance is usually 10 milliohms or less after doing that so I think it's good enough.