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Yamaha A-1 amplifier thump on power off.

H

Hifibythekg

Super Member
Hi,
I have a Yamaha A-1 that I’ve been working on and is now sounding great and has stable readings for Drive Circuit DC Offset, Idling Current, Power Supply voltage as per the manual.

But, powering off just now by pressing the power button on the amp led to a substantial thump through the speakers.

Could this most likely require:

  • replacement of the two spark suppressors?
  • or replacement of the caps on the power board (it still has the original ones, they tested ok but maybe they need renewing?)
  • or is there something else I should check first?
Would be grateful for any advice, thanks.
 
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Great to see you back in action Colin!!!

So I take it the 2SK adaptor board is working fine for you!!!

I would replace the power supply caps for sure, its an easy task . While there remove the two transistors and clean and replace the thermal grease. these get very hot and dry it out, you may notice the board being a little scorched from he heat.
Also for the A-1 changing the relay is almost mandatory .
The spark suppressor caps may be the issue, so replace those.

Athanasios
 
Thanks Athanasios, this is a great help.
And I’m very glad to be able to be back in action here.
And..
“So I take it the 2SK adaptor board is working fine for you!!!”
Silly me to not give huge credit to your beautiful adaptor boards. They fitted perfectly and as far as I can tell are performing superbly.
Regarding the relay, do you happen to know of a model/brand that fits and works well for the A-1. There’s something about this amp that makes me think it’s more fussy than most with regard to component replacement.

Cheers.
 
BTW, this A-1 has its output transistors replaced with MJ21193/4G.
Seems to work great but obviously can’t do a swift A B test. Anyone have any views on this modification?
 
Have you replaced any caps in the protection circuit, C218(100uf/16V) or even C217(0.47/50). What type did you replace them with.
Is the speaker lamp functional? Replaced with LED or lamp?
 
Thanks @mbz and @avionic.

Yes, I did change C218 100uF 16V to a Nichicon UPW(M)
Was this a mistake?
The SM denotes a ‘Z’ cap.. what should this translate to in contemporary components?

C217 I didn’t change, SM denotes an ‘MS’ cap. What would be an appropriate replacement here?

For all the other caps on this board would Nichicon UPW’s be ok?
Would Panasonic FM or FC’s be good alternatives?
Any additional Brand and series combinations would be appreciated as Farnell, my preferred supplier because of shipping costs, don’t always carry the full range of all the components..

The speaker lamp is functional as I replaced it with a lamp, not LED. Pretty sure that it was exactly the right spec lamp.
 
Hifibythekg said:
Yes, I did change C218 100uF 16V to a Nichicon UPW(M)
Click to expand...
UPW/M would be a good choice, likewise for the other caps in the protection/psu circuit. Panasonics would also be fine.

Hifibythekg said:
The speaker lamp is functional as I replaced it with a lamp, not LED. Pretty sure that it was exactly the right spec lamp.
Click to expand...
In some yamaha amps (CR series...) they used the lamps to run down the charge of the protection circuit caps at power off so as to get a quick release of the relay. Using LEDs may result is slower cap discharge/longer relay holding. All good since you used a lamp.
 
Thank you guys.
@avionic did you say that the 'MS' cap at C217 should be replaced by a Wima poly cap of some sort or was this revised, as I can't see it now. Would be grateful for advice on what type I should order for this location.
@mbz thanks. So my C218 Nichicon UPW(M) shouldn't be the cause of the thump.
For Panasonics on the power supply board, are FM or FC to be preferred if I should have a choice?
 
Hifibythekg said:
So my C218 Nichicon UPW(M) shouldn't be the cause of the thump
Click to expand...
A fault free C218 wont cause the thump. More likely a fault in the protection circuit or relay contacts "welded" or ...

Hifibythekg said:
For Panasonics on the power supply board, are FM or FC to be preferred if I should have a choice?
Click to expand...
Don't know that much abaout Panasonics. Looking at the datasheets, I would lean to FM over FC's. From the FM datasheet.
upload_2022-9-17_12-20-32.png

Tan delta and ripple are in the same ballpark as the UPW's so either would be fine.
 
Thanks @KingBubba
Yes, this works. But.. there's more than just me in the house, and not all follow protocol..
Plus, I feel that if the amp's working right that it won't provide a thump in the first place.
 
Actually since mattsd rebuilt my SX-1250 and SX-1280 they both have a small bump both on and off. I use the typical audio mans sequence to protect from transients. I have speakers off and volume all the way down before I fire up the unit. I wait 5 to 8 seconds before I flip on the speakers and volume. I reverse that before turning off the power on the unit.

The big Crown Amps, at the theater where I worked, had to have the volume knobs turned down before they were shut down in order to save damage to the Meyer Speaker clusters. For a while the audio man didn't bother until he lost a Meyer in the main center cluster. After that he also shut the Meyer processor down before powering down the the Crowns. He should have been doing this all along. Dropping the center cluster down was a big pain and involved the use of chain hoists. Not fun.
 
Thanks @KingBubba , yes, good advice. Great anecdote too.
"I use the typical audio mans sequence to protect from transients. I have speakers off and volume all the way down before I fire up the unit. I wait 5 to 8 seconds before I flip on the speakers and volume. I reverse that before turning off the power on the unit."
It's what I've been doing, almost instinctively. Will be interesting to see if the PSU board recap reduces the thump value. At least there's a workaround..
 
@Hifibythekg , Does the thump happen with the speaker switch off as well?

If so it might be as stated earlier that the relay is fused closed, therefore never disconnecting the speakers from signal. That would cause a thump.

Athanasios
 
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