Technic SA-600 Help Please - Balance Control Pot Questions

Joe Nardy

AK Subscriber
Subscriber
I recently acquired a Technics SA-600 for the right price (free) from a friend who was downsizing to move out of state. He was the original owner but it had been in unprotected attic storage for many years including during a roof tear-off and replacement so it looked pretty rough. I removed the covers and blew all the dust and debris from the inside. I cleaned the circuit boards and wiring with isopropyl alcohol and a cheap paint brush. I cleaned all pots and switches with De-Oxit 5. After drying out I powered it up and it appears to function well. I ran a CD player through the Aux channel and it sounded nice, no scratchiness or other odd sounds. The AM and FM tuners seem to function as well. I haven't yet tried the phono input but hope it's good as well. Cosmetically, it cleaned up well and I like its looks.

The only non-functional piece is the balance control. My buddy told me the pot had gone bad many years ago. He replaced it with some generic pot (just so he could have a post to mount the knob) and hard-wired it so the balance is zeroed out and the pot does nothing. I'd like to replace the pot with an original or suitable replacement but am having some difficulty finding the correct value and part number.

I can't seem to find a service manual (or even specs) for the SA-600. I found manuals for SA-500 and SA-700 on Hifi Engine but no luck on the SA-600. It appears that the SA-600 is more similar to the SA-500 than the SA-700 but I'm not sure. The SA-500 manual shows the balance control pot to be 200K ohms while the SA-700 shows a value of 250K.

Does anyone have a service manual for the SA-600 they would be willing to share? If not, any info on the correct value for the balance control pot would be sufficient. Also, if anyone happens to know of a source for a replacement pot or happens to have one they'd be willing to part with I'd be grateful. Specs would be great as well.

I'd love to get this unit fully functional and put it into service. I know it would be fine with the non-functional balance control but that would drive me crazy every time I looked at it.

Thanks in advance for any help anyone can provide,
Joe
 
Last edited:
Really, wouldn't make much difference if you install a 200K or 250K pot. The smaller the value, the transition would be faster. The SA626 has a 100K pot.
 
What type of shaft is it? Spline, D shape? How long? Through hole, wire leads?
 
What type of shaft is it? Spline, D shape? How long? Through hole, wire leads?

The shaft is D-shaped and is about 5/8 inch in length. It is through hole soldered into circuit board. I'm not sure if it is supposed to have position detents like the bass, treble, and volume controls or not. I've sent a message to a forum member who owns a SA-600 asking him about the detents or lack thereof. None of my other receivers with detents on other controls have detents on the balance control so it seems that was uncommon.

Thanks,
Joe
 
I was able to find what I believe is a suitable replacement balance control pot from an SA-200. Again, I don't have a service manual for my SA-600 but it is supposed to be very similar to the SA-500 which I do have a manual for. Both the SA-200 and SA-500 show the balance control pot as 200K and the schematics are very similar.

I replaced the pot but still have no balance control. Everything else (bass, treble, high and low filters, and volume controls) seems to work fine and the unit sounds good. I gave the pot a good cleaning with DeOxit5 and checked the resistance. It all seems fine. I can't detect any difference in volume on either channel when turning the balance pot.

I have reasonably good skills with VOM and decent soldering skills but lack in using schematics. I can see that this is a pretty simple part of a circuit and should be somewhat easy to figure out.

Any help or suggestions you can provide will be greatly appreciated.

Thanks,
Joe
 
Most likely you wired it incorrectly. You should have ground running to the center pin (cursor), and each channel signal to the pot end pins.
 
Most likely you wired it incorrectly. You should have ground running to the center pin (cursor), and each channel signal to the pot end pins.

Thanks for the reply but I don't think that's the case. The pot is board mounted with three pins. I can't see how it could be connected incorrectly.

However, I am seeing some strange resistance readings. With the balance pot removed, measuring at the board, I'm getting just 3 ohms between center and one outside hole, around 1.5 ohms between center and the other outside hole. I have enough electrical knowledge to know that if there's that small resistance within the circuit the much larger resistance of the balance control pot will be irrelevant.

So, why would the resistance on the board be so low without a balance pot installed?

Thanks,
Joe
 
That's the volume pot down to zero messing with you.. lol. Just crank it CW and your readings will get higher.

Regarding the balance pot, check out with your meter you have proper ground at the center pin, otherwise it'd not work at all.
 
That's the volume pot down to zero messing with you.. lol. Just crank it CW and your readings will get higher.

Regarding the balance pot, check out with your meter you have proper ground at the center pin, otherwise it'd not work at all.

Thanks again. The balance pot works fine, verified with ohm meter. With the pot centered I get roughly 100K ohms between center pin and each outside pin. If I crank the knob fully CW or CCW I get the same 100K ohms measured from center to one outside pin and close to 0 ohms between center pin and the other outside pin. The measurements change sides when the pot is rotated the opposite direction.

The pot is not installed on the board. There is nothing mounted to the balance control pot holes on the board. The resistance measured between the mounting points on the board is just a few ohms between all three points. If these resistances are this low the much higher values of the pot will be ignored unless my electrical analysis is incorrect. Please correct me if I'm wrong.

Thanks,
Joe
 
Thanks again. The balance pot works fine, verified with ohm meter. With the pot centered I get roughly 100K ohms between center pin and each outside pin. If I crank the knob fully CW or CCW I get the same 100K ohms measured from center to one outside pin and close to 0 ohms between center pin and the other outside pin. The measurements change sides when the pot is rotated the opposite direction.

The pot is not installed on the board. There is nothing mounted to the balance control pot holes on the board. The resistance measured between the mounting points on the board is just a few ohms between all three points. If these resistances are this low the much higher values of the pot will be ignored unless my electrical analysis is incorrect. Please correct me if I'm wrong.

Thanks,
Joe

Joe, in regard to the pot readings, it's correct the pot reads 100K from center to each outside pin when the pot is centered. When it's fully turned CW or CCW, it should read zero from center to one outside pin, and 200K from center to the other outside pin (It's a 200K pot, is this OK?

Regarding the low resistance values you read at the balance pot holes on the board, again, that's because your volume pot is fully CCW. Turn it (the volume pot) CW and your readings will get higher.

Please check out that you have proper ground at the center hole for the balance pot. Otherwise there will be NO balance transition once you install the pot on the board.
 
Joe, in regard to the pot readings, it's correct the pot reads 100K from center to each outside pin when the pot is centered. When it's fully turned CW or CCW, it should read zero from center to one outside pin, and 200K from center to the other outside pin (It's a 200K pot, is this OK?

Regarding the low resistance values you read at the balance pot holes on the board, again, that's because your volume pot is fully CCW. Turn it (the volume pot) CW and your readings will get higher.

Please check out that you have proper ground at the center hole for the balance pot. Otherwise there will be NO balance transition once you install the pot on the board.

Sorry, I misread the first post and didn't see you were talking about the VOLUME pot. I think I've made some progress. I cleaned the pot contact area on the board with isopropyl alcohol and now I'm getting some more appropriate readings between the contacts. The volume setting doesn't seem to affect the readings but I'll keep it fully CW.

I think you may be onto something with the ground. I don't seem to have a good connection to ground from the center hole right now. However, it appears that there is a capacitor between the pot connector and ground. I have a short between the center pot hole and one side of the capacitor but some resistance (roughly 20K) across the capacitor. Is this a problem?

<EDIT> The schematic shows the capacitor and it appears to be 16V 33mf.

Thanks,
Joe
 
Last edited:
I think I'm on the right track. I now have logical readings. With the pot not soldered in but jumpered to the correct pins I have readings of:

Pot centered - 34K ohms center to left, 34 K ohms center to right, 68K ohms right to left.
Pot fully CW - 34K ohms center to right, >1 ohm center to left, 34K ohms right to left.
Pot fully CCW - 34K ohms center to left, >1 ohm center to right, 34K ohms right to left.

I'm going to test and will report back.

Thanks,
Joe
 
YES! All back together and working. Rather than solder the pot back into the circuit board I ran short wires to common connection points. Space is very tight and I didn't want to do a lot of disassembly.

Now the pot I got is acting up a bit. I think I overheated the contacts while soldering and they aren't making perfect contact with the resistor surfaces of the pot. It seems to work fine unless I really push and pull on the pot knob. At least now I can easily swap in a different pot and don't need to find a board mount type.

Thanks for all the help,
Joe
 
Well done, Joe. Did you discover what was wrong with the center hole ground? Clearly now that's fine since the pot operates as intended.
 
Well done, Joe. Did you discover what was wrong with the center hole ground? Clearly now that's fine since the pot operates as intended.

Thanks for your help on this issue. I believe the cause of the problem was some sort of conductive gunk around the PC board connection points. Regardless of whether or not the pot was installed there was only 2-5 ohms of resistance between the points. Once I cleaned the board with isopropyl alcohol and a brush the resistance readings were 300K-600K ohms without the pot and 35K-70K with the pot. The resistance values also changed as expected with rotation of the pot.

Joe
 
Thanks Joe! Many thanks! I didn't realize how much work you put into this, until I found this thread.


I was the guy Joe got this from. Last month we went back to Illinois and spent some time with Joe and his wife. Joe played it for me and it was very nice. When we got ready to leave, he gave it back to me, ready for our new home, along with some RS Nova-7B speakers.

Great guy.
 
Really nice gesture and story. Thank you very much for sharing (3 years ago, I realize ha).

Separately, this thread inspired me to swap out my own favorite Technics SA-500 from the work pile that has a non-functioning volume pot with my SA-200 with a dead right channel's volume pot. Several hours of horribly embarrassing desoldering and soldering, burning stuff later and dang, the SA-500 is up and running again as of last night sounding sweet as ever!

Thanks, again for the info share!
 
Back
Top Bottom