Another C-70 channel dropout issue

[sjsingle1]

Newbie here, but long time audio enthusiast. I have a C-70 I bought when stationed in europe in the 80s ( I loaded up on lots of low priced high fi !! ) and its one of my favs. In the 90s it developed a channel issue that a local worthless repair shop fixed with a install of a new balance pot ( knob ? ) it did not fix the problem so into non use it went for all these yrs. Now I would like to fix it up to pass on to my son so off to the best local repair shop I can find. First shop was no better than the one I used in the 90s, so back to searching, so find success in my search for a shop and drop it off for a overhaul ( recap and so forth ) I quickly find the relays...HB2E-DC24V ..are hard to find but managed to get my hands on some. So everything under the hood is spanking new and I pick it up only to later find I STILL have my drop out issue, to be honest I just casually mention this issue and hope the overhaul does the trick.

My repair guy is the best local to me ( he is great with tube macintosh's FWIW ) but he is having a hard time fixing this problem, anything I can tell him to point him in the right direction or should I just send it to someone anybody can recommend who has experience in these pre amps ?

 

[sjsingle1]

Oh...I only get the dropout with the tone control engaged

 

[mbz]

Certainly, intermittent problems are hard to track down. The relays do have a history of going internittent. Mine are
due to arrive in the next few days, sourced off ebay from china, not much hope. However of greater concern are all the dry solder
joints in the C-70 (well, mine at least), about 50% of the joints looked suspect, worst case I've seen. Google dry solder joints
for pix however your tech will know this.

 

[avionic]

Welcome to AK.. Have your tech look at SW503. It will need to be disassembled and cleaned.
It's a solenoid operated switch. Located under the (Tone Control Circuit board 2) on the left side main board.

 

[sjsingle1]

SW503 ? a member here ?

 

[avionic]

Red X marks the switch

 

[avionic]

SW503 ? a member here ?

No .. SW503 is switch 503

 

[sjsingle1]

Oh ...OK....lol.....I went to electronics school at Keesler AFB but damm if I can remember anything I learned there

my tech did mention he had to pull up the tone control board from under the main board and what a PITA is was

 

[avionic]

I'm going to tell you flat out. Just trying to spray cleaner inside that switch will not get it clean. It needs to be disassembled.

 

[avionic]

.I went to electronics school at Keesler AFB

I went to Lowry AFB --- F/FB-111 and F-15 electronic warfare component specialist.

 

[sjsingle1]

is it a switch ? relay? or ?

did you have this problem on your C70 ?

I went to Lowery AFB too.....for Disaster Preparedness school

 

[avionic]

is it a switch ? relay? or ?

did you have this problem on your C70 ?

I went to Lowery AFB too.....for Disaster Preparedness school

Solenoid operated switch. I repair and refurb C-70's among other Yamaha separates quite frequently.
Highly recommend replacing all 8 of those HB2 relays.

 

[sjsingle1]

I had all those HB2s replaced !!

 

[avionic]

I all those HB2s replaced !!

OK.. Wasn't sure if you replaced a couple or all of them.

 

[avionic]

What's your geographic location?

 

[sjsingle1]

texas, fort worth

happened to have those HB2 right in front of me at the computer

 

[sjsingle1]

 

[avionic]

Them be the ones.

 

[Oldsansui441]

However of greater concern are all the dry solder
joints in the C-70 (well, mine at least), about 50% of the joints looked suspect

+1 on this, these Yamaha's are notorious for poor joints. Currently working on a C-85 which has already taken many hours of reflowing also. Certainly not saying it couldn't be the switch that avionic suggested though.

Does your channel drop out occur on any input or only one?

 

[mbz]

Does your channel drop out occur on any input or only one?

Good question.