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Yamaha C4 preamp fault. Hum. Phono switches.

I took this ones
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I measured the reeds with 3-4 Ohms within the contacts, the Takamisawa with "0" Ohm. Also the power consumption may be a little bit lesser than like the reeds.
 
Have to say I’m very impressed with the appearance of these, and other, components on the board. Are the relays kept in place only by the rigid green and white covered wires?
How do you like your C4 after the changeover to metal film resistors and MKP caps etc etc?
 
Yes ist seems to be the same, but take attention to get th 12V type.
The green wires were recycled from telephone cables... ;)

For more about my project I will report later in a seperate thread. It's not accomplished yet so I can't say anything about the sound...:dunno: It seems to coming up weekend that I switch for first time after rebuilding "power on". I fear some issues...may be I had made some mistakes....I had changed a lot.
 
Thanks, well I hope that all goes well for you with power on, and look forward to hearing your review of its performance.
But are you pretty sure that the Takamisawa works well in this position.
If so, I'll just order one rather than mess around switching my reed relays from other working amps.
As it hasn't been fully powered up or tested I should probably ask whether anyone else has a view on the best relay substitute in this position?
 
In the german speaking datasheet were wrote as follows:

Contacts made with AgPd/Au
Contact resitance ≤50mΩ
Max power on contacts 0.5A / 125VAC

But there you have less than 1V and less than 0.1A

This relays were used in many audio circuits. So I had no doubts to order them.
 
There were only small signal currents switched, 12V DC was regulated by the power supply, also with 240V AC. In Germany we have 230V AC.
 
Have you gotten your power supply working yet ? No 12vdc power supply--no relay worky..!
 
Good grief....
I'd checked and then checked again every fuse in the amp, and all very good.
In the UK we have adapter plugs to convert a two pin to three pin mains socket.
Only now did I remember to check it.
Yes, a one amp fuse. Yes, it's blown.
Never blew before with this amp, the disconnected blue wire to the power switch had triggered it, at least I hope that that's the cause.
So, have replaced the adapter fuse with another 1 amp fuse and am reassembling the boards and chassis screws. Will report back when I power up.
Apologies for this 'oversight.'.....
 
Ok, amp powering up and working 'perfectly' again, except for the exact same hum.
Really, the sonics with a source through either Aux or Tuner is superb.
Just completely rechecked and flowed the RCA jack board.
But there is bleed through of audio from Aux to Tuner.
When on Phono 1 and 2 the hum is loud. When on MC even louder. Rotating the completely disassembled and serviced Cartridge Load switches has no effect at all on the hum when Phono1,2, MC selected or at any combination of the selector switches.
Hum equal on both speakers.
The PSU and flat amp boards have already been recapped.
What can it be?
Would a tech with a scope be likely able to track it down fairly easily?
Was about to recap all the Function Circuit Board, and maybe re-diode it too or is there something else I should do first.
Life is short...
Further suggestions welcome.
 
It did exist with all the covers on a few weeks ago after some repair work and prior to a second round of servicing.
But I can put the covers back on again to see if it makes a difference.
Although I thoroughly serviced the wafers, is it possible that the Function or Tape selector wafers could cause this hum if I’ve missed something in the contacts?
 
After checking the covers being screwed back on, what next?
Wholesale replacement of all diodes on the PSU and flat amp?
Wholesale replacement of all caps on the Function board?
Check wafers again? (although flexing and tapping them doesn’t alter anything.)
Tapping stuff around the board doesn’t generate any changes at all, unfortunately.
 
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