Yamaha C-80 lost sound switching inputs

[Sparkplug]

TR340 abd TR341 are 15.03 and -15.07 VDC at the emitters, That seems right on.

IC309 - now I'm not sure which side is pin 1 and which is pin 10. I can't tell from the schematic or the printed circuit board diagram so I'll try it both ways

With tone control board #2 installed in the unit assuming the bottom most pin is #1:
pin 5: 13.3 V
pin 9: 15.11 V

Assuming the top most pin is #1
pin 5: 13.1 VDC (same pin either way)
pin 9: 15.1 V.

Ok so I don't see a -15 anywhere. Hmm did I install the wire connecting to tone control board #2 the wrong way around?

The cut corner side on the IC is pin 1:



Pin 5 (IC309B) should be -15V based on the schematic. NJM4558S is a 9-pin op-amp. You mentioned pin 10, make sure you’re on the right IC (LOL). See below circled in red. Never mind other marked stuff, not related to this case.

Edit: IC309A and IC309B are two halves of the same op-amp IC309 which is a two op-amp part.

 

[Soundscape]

NJM4558S : Looks like pin 1 is on the notched side of the part case.

 

[avionic]

Hmm did I install the wire connecting to tone control board #2 the wrong way around?

If you did. The 4558 IC is toast. Maybe a poor solder connection or cracked solder pad on your two-wire connector.

 

[Sparkplug]

If IC309B pin5 is not -15V or is positive, the IC is toast.
Edit: The correct cable (±) orientation is shown in the PCB layout given in the SM. Plus bottom, negative top.

 

[ghankstef]

I do have the cable soldered in correctly according to the service manual PCB graphic for tone control board #2. .

Ok pin 1 is at the top of the board when the board is installed in the unit. I mistakenly counted 10 pins because it looks that there is a resistor leg soldered in just above where the IC is soldered in on the board. Pin 9 is 15V as it should be but pin 5 is 13V not -15V so I think I can conclude IC308 is bad. Earlier discussion in this thread indicates that there isn't a drop in replacement for IC309.

I would rather have a functioning loudness control than the mute functionality. If I unsolder the cable the loudness control pot works perfectly. I don't think I would use the muting anyways. If I leave the cable unsoldered, will that effect anything else?


Huh quick google search brings this up: https://www.rfparts.com/njm4558s.ht...JXBPYgUw56pyjsvH1DK0QMWOfkfWf5lW0qk0xdZLOuHCp. Don't know that I can trust the company and that NOS part will be good but then again - less than 2 bucks but $16 shipping - geez.

 

[Sparkplug]

Huh quick google search brings this up:

This is not the same part, this an 8-pin newer op-amp. The one in C-80 is a 9-pin chip often used in pre-amps of that era. Most had a pin for phase correction/control, not sure about NJM4558S, don’t have its data sheet.

Edit: Their website lists the 9-pin version NJM4558S as well. Maybe you should call them to make sure, their website looks legit but $16 delivery charge is outrageous. I’d call them.

If I leave the cable unsoldered, will that effect anything else?

I’m still not clear where that cable exactly comes from and where it goes. In disconnected state, what voltages do you measure on each of white and red wires?

 

[Sparkplug]

I also found this while searching for NJM4558S. It’s NJM4560 but they’re from the same family and pinout would be the same.

 

[Sparkplug]

While you’re at it, could you measure the voltage at pins 5 and 1 of IC306A? Just want to make sure the -15V is present. See below

 

[Sparkplug]

Unfortunately the IT Dept. where I work . Blocks downloads to my HiQ scans as well as HifiEngine.

Yes, they’ve caught up with you …

 

[ghankstef]

Loudness now working! @Sparkplug gave me the clue Transistors TR340 and 341 in the muting curcuit measured 15V and -15V on their emitters so I assumed the problem was not on that end of the cable. Turns out one leg of the cable had a bad connection - soldered that bad boy back in there good and back in business.

So the original volume/loudness pot may or may not have been the issue. Maybe it was just the loose leg on the cable. Either way I'm happy.

Could button it up and have a very nice preamp now. Only 3 inputs are working though - which is almost enough - I think I know why but not sure what to do about it. Tape 2 is busted and somehow that prevents Tape 1 and Aux from working. Still even if that stays that way 3 inputs is workable.

 

[Sparkplug]

Loudness now working! @Sparkplug gave me the clue Transistors TR340 and 341 in the muting curcuit measured 15V and -15V on their emitters so I assumed the problem was not on that end of the cable. Turns out one leg of the cable had a bad connection - soldered that bad boy back in there good and back in business.

So the original volume/loudness pot may or may not have been the issue. Maybe it was just the loose leg on the cable. Either way I'm happy.

Could button it up and have a very nice preamp now. Only 3 inputs are working though - which is almost enough - I think I know why but not sure what to do about it. Tape 2 is busted and somehow that prevents Tape 1 and Aux from working. Still even if that stays that way 3 inputs is workable.

Just saw the photo. Make sure those red/brown/orange cables are making good connections on both ends. If C-80 followed the C-70 convention, those cables plug into some pcb mounted connectors with a latch to lock them in place. If the cables have moved or have been/seen some strain, they may not be making connection. In this case I suspect the lower three wire cable. Pull out, clean or cut and strip anew, and insert back in. When inserting, do not bend the cable at right angle.

Solder connection checks are also a must.

 

[ghankstef]

Just saw the photo. Make sure those red/brown/orange cables are making good connections on both ends. If C-80 followed the C-70 convention, those cables plug into some pcb mounted connectors with a latch to lock them in place. If the cables have moved or have been/seen some strain, they may not be making connection. In this case I suspect the lower three wire cable. Pull out, clean or cut and strip anew, and insert back in. When inserting, do not bend the cable at right angle.

Solder connection checks are also a must.

Excellent tip. Thank you and will do

 

[ghankstef]

Good deal was able to replace the missing part for tape 2 input from my parts unit and tape 1,2 and aux all work

Sometimes the switch buttons don't stick and the LEDs aren't firing so need to figure that out and then I think this thing is ready to go. Even the pop from turning it off is gone. Maybe replacing some of the caps helped.

 

[ghankstef]

@Sparkplug called it again some of the connections on the input selector board were loose or even disconnected - some of that might have been my own doing while I have been working on it. It was a little tedious to unsolder all of the connections, strip and new bit of wire and tin it, and then re-solder them but now all the inputs work and so do the LEDs. So now just one more test on the test system and then put it all back together and enjoy it assuming the test is good.

 

[Soundscape]

@Sparkplug called it again some of the connections on the input selector board were loose or even disconnected - some of that might have been my own doing while I have been working on it. It was a little tedious to unsolder all of the connections, strip and new bit of wire and tin it, and then re-solder them but now all the inputs work and so do the LEDs. So now just one more test on the test system and then put it all back together and enjoy it assuming the test is good.

Go Sparky!

 

[Soundscape]

Sometimes the switch buttons don't stick

I've done 3 of these amps and saw other members with similar tactile switch issues. Swamp and cycle with cleaner of choice. Then swamp and cycle more until the can is gone. Lol. IIRC there's an open area of the switch rail to the right side for prime squirting.
EDIT: nice determination on your part OP, all and all. Let the swamp dry for a couple days afterward, lay the unit on different ends every 12 hours to dry out, IMO.

 

[ghankstef]

I've done 3 of these amps and saw other members with similar tactile switch issues. Swamp and cycle with cleaner of choice. Then swamp and cycle more until the can is gone. Lol. IIRC there's an open area of the switch rail to the right side for prime squirting.
EDIT: nice determination on your part OP, all and all. Let the swamp dry for a couple days afterward, lay the unit on different ends every 12 hours to dry out, IMO.

Thanks much. Seems to be working well now. I did another round of contact cleaner and cleaner with lubricant. Think I have done 3 rounds now.

 

[Soundscape]

Thanks much. Seems to be working well now. I did another round of contact cleaner and cleaner with lubricant. Think I have done 3 rounds now.

I can't remember the where or when thread...but I do remember @nakmandan working those switches on a C-60 I think. He was taking ohm readings across the switch after each swamping round. It got lower and lower and called it good after 5 rounds IIRC.

 

[ghankstef]

I can't remember the where or when thread...but I do remember @nakmandan working those switches on a C-60 I think. He was taking ohm readings across the switch after each swamping round. It got lower and lower and called it good after 5 rounds IIRC.

Ok maybe I'll do one more before putting humpty dumpty back together again.

 

[Sparkplug]

@Sparkplug called it again some of the connections on the input selector board were loose or even disconnected - some of that might have been my own doing while I have been working on it. It was a little tedious to unsolder all of the connections, strip and new bit of wire and tin it, and then re-solder them but now all the inputs work and so do the LEDs. So now just one more test on the test system and then put it all back together and enjoy it assuming the test is good.

Good work. Enjoy.