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Yamaha A-1 speaker cut out

H

Hifibythekg

Super Member
My nearly perfectly restored Yamaha A-1 still randomly cuts out!
Power stays on and no fuse blown or magic smoke and amp runs relatively cool.

All caps have been replaced.
Brand new Omron speaker relay replaced.
Offset, idling, all very stable and correct from the service manual.
Most of the solder checked and reflowed.

It sounds absolutely stunning using the Canton Plus-S speakers.

What can be causing this?
What things to check as I have no idea how to fault find at this point.

Grateful for any advice as I really want this amp to be in full time use.
 
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Check the voltage regulators for the relay. I found that if they get extremely hot it may cut the relay out. I remember using freeze spray while it was out on one of the PS transistors brought it back. I can't remember if I replaced it or just cleaned up the thermal paste and added another heat sink for better heat dissipation .

Athanasios
 
Thanks Athanasios.
Please can you tell me which components are the voltage regulators?
I've attached the circuit board layout diagram.
Screenshot 2022-10-26 at 21.32.11.png
 
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Switched it again and switched it on after about an hour.
Plays perfectly, then after 10 mins.. a sense of power through the speakers ('whoomph' sound) and speaker relay cuts out.
Again, power light stays on and no other issues.
 
Its on the electrolytic capacitor board, looking at the schematics I believe its TR 215,and TR 214 also make sure that Zener diode D205 is working ok.

TR 215 feeds TR 214 in next schematic snippet
52457157010_111b8efe8f_h.jpg


TR 214 12 volt out on pin 10
52456719076_6bdec5c0f6_b.jpg



Relay 12 volt in at pin 10 in this schematic section

52456992189_f9b802f368_b.jpg

52456972994_8ae8143fa9_h.jpg
 
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Thanks!
Will check both.
The transistor is a 2SD526, do you know what's the best replacement?
Also, on another thread somebody had a problem with a 2SB566 at TR201 on the power supply board which I believe some have recommended replacing with a TIP32C, or an MJE15033G. Any thoughts on this?
 
Sorry just re read your post and
TR214 is 2SC673A
TR215 is 2SD526
so also need to know the best replacement for a 2SC673A in this location.
 
Hifibythekg said:
Thanks!
Will check both.
The transistor is a 2SD526, do you know what's the best replacement?
Also, on another thread somebody had a problem with a 2SB566 at TR201 on the power supply board which I believe some have recommended replacing with a TIP32C, or an MJE15033G. Any thoughts on this?
Click to expand...

Hifibythekg said:
Sorry just re read your post and
TR214 is 2SC673A
TR215 is 2SD526
so also need to know the best replacement for a 2SC673A in this location.
Click to expand...

Hifibythekg said:
For the transistors and the zener diode, best to remove and test out of circuit?
Click to expand...

I´d just try to reflow the soldered connections first.
 
Thanks @avionic , appreciated as always.
Yes, it could very well be a poor solder join heating/flexing causing the problem.
As well as the transistors and diodes mentioned above, is there any other location you think I should especially examine?
Is the faulty location most likely located on the ‘Power Supply Capacitor board’?
 
Did all the work but just tested the amp and after about an hour, turned the volume up and down and a few seconds later it made a crackle and the speakers cut out.

Works so far:

Have installed brand new relay.

Reflowed solder on entire Power Supply board.

Recapped entire Power Supply board.

Reflowed solder on entire Electrolytic capacitor board.

Tested TR214 and TR215 out of circuit. Both ’good.’

Replaced Diode 205, although the original tested good.

Haven’t yet tested the voltages as kindly advised by @Nashou66 but will try to do this despite the awkwardness of access to some points.

When I go back in, whilst there is there anything else I should check in the hope of tracking down the cause of this fault?
 
Did you clean the switches? Sometimes those lose contact and can cause crackling etc.

Also what source are you using when the cradle happens. is it on all inputs?

Athanasios
 
Yes, cleaned the switches and the pots were generally very clean and no scratching.
Am now going to check for any more solder spots suspect traces.

Because it cuts out after an hour or so, when it’s heated up, this suggests that it’s heat related and is very possibly a poor connection made worse by thermal expansion.
Especially as just leaving it switched off overnight allows it to power up the next day.
Leaving it for an hour or so allows it to power up and then speaker cut out after about 10 mins.
Would any of you techs at this point start spraying freeze spray on the most likely areas, or is there a more rational set of procedures to go forward with?
Do some faulty transistors or other components have a reputation for playing up once they’re heated?
 
I had the same issue , where even with no source on I could hear the scratchiness through the speakers .

I forgot what I did but I think it was a disassembly of the push button switches, not sure which one. I think it was one near one of the lights, either the speaker of the Disc switch. The lights put out some heat and it could be something near them. I haven't turned that unit on in a long time but for the week or so after the fix I forgot , lol, it worked fine. I should bring it out and see if the issue has come back, its been well over a year since I have used it.

Athanasios
 
Also check the 4.7 ohm resistors R109-112 . These are carbon film and IIRC i had a couple that drifted high.

There are also two 1 watt 4.7 metal oxide resistors I think that it might have been those, I know the value was 4.7 ohm. R121,122

Athanasios
 
Just powered amp on after having reflowed more solder on the power supply board and the electrolytic capacitor board.


No power light, no speaker light, no sound!

Switched off at the mains after about 8 seconds.

Checked mains plug fuse, main fuse at the back of the amp, all 3 fuses on the power supply board - all good.

Checked pilot fuses and all have continuity.

But… the big caps had charged up to their usual 45 Volts!


How should I now proceed?
 
Just saw your new posts, thanks. Will also check them but I think I checked those resistors before and they were ok, but will check again.
In the meantime the non/silent power up is a strange new twist..
 
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