500C Tape Monitor Switch

Chappy

Active Member
I recently cleaned all of my switches and pots on my 500C with DeOxit. Before I cleaned it I noticed that one channel would sometimes cut out with the Tape Monitor switch in the OFF position. It was obviously dirty and I have fixed that problem. Now I have noticed that I have signal bleed through with the switch selected ON. I can't remember if my receiver did this before I cleaned the switches and pots.

My setup.

CD player into AUX inputs.
FM antenna
1 set speakers hooked up to Speaker 1 outs.
No other connections.

My cleaning procedure.

DeOxit D5 sprayed into pots, and all 4 sliding switches.
DeOxit D100L liquid used to clean all of the rotary switches.

With a CD playing, flipping the Tape Monitor ON gives significant bleed through on both channels.
With the FM selected (all three positions) I get a very small amount of bleed through which is not balanced. A bit more on the right channel.

I don't believe that this is normal. Is the Tape Monitor switch the culprit as a result of my cleaning or should I be focusing my efforts elsewhere?

Chappy
 
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With the Tape Monitor switch "ON", you should have no output at all. Sometimes the little sliders in the switches come loose or even break. I had this happen on my 500B. I removed the switch and took it apart and had to bend the tangs on the slider contacts that were loose.
 
With the Tape Monitor switch "ON", you should have no output at all. Sometimes the little sliders in the switches come loose or even break. I had this happen on my 500B. I removed the switch and took it apart and had to bend the tangs on the slider contacts that were loose.


That was fast! Thanks. So it's possible that in removing the gunk inside the Tape Mon switch, I have now created a conductive path allowing the signal to partially bleed through? The CD bleed through is about half of full volume so I don't think I have full metal on metal contact.

Chappy
 
I'm not the best where it comes to technical questions but I found the problem with one of the slide switches in mine with the faceplate removed, I could see one of the contacts was sticking out in on or off and wasn't making full travel with the switch. Plus, the switch didn't "feel" right. I tried pushing it back into place and it would do the same thing so I carefully took the switch apart and found the weak tang. I had to put a bit of solder at the bend as it was getting very weak and was ready to break. With the switch opened up, you could really clean it up nicely.

If you plan to try it, pry the switch apart using just enough force to pop the switch apart without bending the housing.
 
I'm not the best where it comes to technical questions but I found the problem with one of the slide switches in mine with the faceplate removed, I could see one of the contacts was sticking out in on or off and wasn't making full travel with the switch. Plus, the switch didn't "feel" right. I tried pushing it back into place and it would do the same thing so I carefully took the switch apart and found the weak tang. I had to put a bit of solder at the bend as it was getting very weak and was ready to break. With the switch opened up, you could really clean it up nicely.

If you plan to try it, pry the switch apart using just enough force to pop the switch apart without bending the housing.

Copy, thanks. I'll leave it alone for now as I don't use the monitor option yet and it is working fine in the Off position. I need to work on replacing the electrolytic caps first.


Chappy
 
Chappy. The CD is in AUX-TAPE position on the selector. Aux and TAPE MONITOR are on the SAME CIRCUIT, Just at different stages. Because the Tape monitor is 1 stage after the phono, it's got less gain to it than AUX-TAPE. Sources played thru the AUX will also play thru the TAPE MONITOR but at a lower level. This is NORMAL due to the way the circuit is run.

As for the FM Bleed over, look for a loose ground inside the unit. Also lines running parallel (Tuner output and the Tape monitor lines) If so, Try and get them perpendicular and away from each other. My 800-C does the same thing. All you can do is minimize it. It's a flawed design, and not much can be done for it.
From the 800-C owners manual. 500-C is identical except for the AM BAND.

attachment.php



Larry
 
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Larry,

Thanks for the info. I just figured this out myself looking at the schematic. It shows the AUX input going through a 330K //120pf cap directly to the MON IN RCA jack. That 330k resistor in combination with the resistance inside PEC4 is probably accounting for the volume drop with the Monitor switch in the ON position. I will look for bleed through on my FM. It's possible that I have left a few cue tip strands behind on the rotary switch. Or perhaps I accidentally created a high resistance circuit path on one of the wafers in the selector switch. I have read that getting these wafers moist with cleaner is a big no no as it can cause conductivity within the wafer. I have proven this to be correct with an old VTVM I have where the battery leaked all over the selector switch wafers. I'm able to measure conductivity across the wafer material with my DVM.

Thanks for the attachment. You have just shown me that I can hook up my AKAI 635D RTR (line signal level) to the Monitor IN RCA jacks.


Chappy
 
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Sources played thru the AUX will also play thru the TAPE MONITOR but at a lower level. This is NORMAL due to the way the circuit is run.

Larry

I see this on the schematic also. With the selector switch in AUX a signal that enters the unit via the MON IN RCA jacks will go through that 330K resistor before finding its way into the selector switch just as a signal hooked up to the AUX RCA jacks would. However, if you flip the TAPE MONITOR switch to ON then that signal goes directly to PECs 3/4 then into V14 so it might result in a higher level signal. I will try this out later tonight.

Chappy
 
Just don't have both turned on at the same time. You'll get interference from one or the other. Learned that a long time ago with a cassette deck on Aux and my GX-730D in the MON in. I had a 3 position Radio shack Tape control switch box, so i put that in between the 800-C and connect all the tape decks and TV thru that. Do the switching and dubbing thru the tape control box. Now i can leave them all on and switch them in and out when I need to. Works with ceramic cartridge loaded turntables too.

Larry
 
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