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Yamaha A-1 amplifier thump on power off.

Hifibythekg said:
Thanks again Athanasios.

Now, a query about the ‘Disc’ button…

if I’m playing music via the Aux input (from a CD player) should depressing the Disc button:

  • just affect the sound a little because it’s bypassing the tone controls
  • OR
  • cut out the sound completely from the Aux input (because ‘Disc’ is designed to work in conjunction with the Phono input.)
Click to expand...

It takes Phono direct to amp , they called a record a Disc before CD's came out ;)

Nashou
 
Thanks Nashou, yes, I’d forgotten that records were referenced as ‘Disc.’
Now, my question is a bit more particular as I try to get this amp going again after the power board’s recap.
Should pressing the Disc button cut in and cut out the Aux’s signal as I play a CD through the amp?
 
Hifibythekg said:
Thanks Nashou, yes, I’d forgotten that records were referenced as ‘Disc.’
Now, my question is a bit more particular as I try to get this amp going again after the power board’s recap.
Should pressing the Disc button cut in and cut out the Aux’s signal as I play a CD through the amp?
Click to expand...


Yes it does., It cuts all other inputs and switches the phono into the amp section directly bypassing all tone controls etc.

Athanasios
 
Nearly there and amp is up and running with no obvious issues. Thump at power off no longer happening after the recap.

Now adjusting the Idling Current and have a new question.

Using a DMM.

To get the correct polarity on the readout (the SM says connect to the DMM’s ‘+’ and ‘-‘ terminals, however my DMM doesn’t have these symbols on the selector dial.)


Connecting TP1 to the DMM’s ‘V Ω Hz F’ input
and TP2 to DMM’s ‘COM’
allows me obtain a stable +7.4 mV


However, if I reverse the leads (as per the SM?) I obtain -7.4 mV but can only adjust the Bourns pot to -0.3mV before the pot reaches its limit of adjustment.


Question:

Is the first arrangement of leads the correct set of connections for adjusting the Idling Current ?








OR

Vice versa?


Doing the first option allows me obtain a stable 7.4 mV

However, if I connect with the ‘vice versa’ arrangement I get -7.4 mV but can only adjust the Bourns pot to -0.3mV before the pot reaches its limit of adjustment.
 
Hifibythekg said:
Nearly there and amp is up and running with no obvious issues. Thump at power off no longer happening after the recap.

Now adjusting the Idling Current and have a new question.

Using a DMM.

To get the correct polarity on the readout (the SM says connect to the DMM’s ‘+’ and ‘-‘ terminals, however my DMM doesn’t have these symbols on the selector dial.)


Connecting TP1 to the DMM’s ‘V Ω Hz F’ input
and TP2 to DMM’s ‘COM’
allows me obtain a stable +7.4 mV


However, if I reverse the leads (as per the SM?) I obtain -7.4 mV but can only adjust the Bourns pot to -0.3mV before the pot reaches its limit of adjustment.


Question:

Is the first arrangement of leads the correct set of connections for adjusting the Idling Current ?

OR

Vice versa?


Doing the first option allows me obtain a stable 7.4 mV

However, if I connect with the ‘vice versa’ arrangement I get -7.4 mV but can only adjust the Bourns pot to -0.3mV before the pot reaches its limit of adjustment.
Click to expand...

there is no polarity setting on the DMM, the black probe is connected to the negative or GND and the red is the positive + connection.

The 7.x mV reading should be done in the positive mode just to make sure your not already in the negative zone which it shouldn't be. That most likely happens if the probes are reversed , and if you know they are, a Negative reading of 7.x mV is ok.

Athanasios
 
Ok, this sounds good. I'll leave things as they are.
Am about to adjust the EQ DC Offset which hasn't previously been adjusted so still has the non-Bourns pots that can be temperamental..
 
Hifibythekg said:
Ok, this sounds good. I'll leave things as they are.
Am about to adjust the EQ DC Offset which hasn't previously been adjusted so still has the non-Bourns pots that can be temperamental..
Click to expand...


yes and that ties in with the 2SK100's that gave me issues. Removing them and cleaning the legs and re installing them solved my Offset issues on that board( which is a pain to get to) .

Athanasios
 
OT's are MJ21193G's.
Had to replace all of them because I couldn't track down an original one that had blown.
Wish I could do an A/B to see if there's much, if any, difference detectable in the sonics.
 
Hifibythekg said:
OT's are MJ21193G's.
Had to replace all of them because I couldn't track down an original one that had blown.
Wish I could do an A/B to see if there's much, if any, difference detectable in the sonics.
Click to expand...


when I had to replace mine I found some originals and bought a few extras to have on hand as I have about 5 of these A-1's .
 
Hi guys.
A-1 has been sounding awesome.
Recently got a set of Canton Plus-S and the matching subwoofer and the sonics are fantastic..
BUT.. the amp suddenly cut out!!
Speaker light went off. I immediately switched off the amp by its power button.
Rigged the amp up to two test speakers and powered it back on 10 mins later.
After 3 mins it cut out again with the speaker light switching off, although the power (white) light was still on.
No nasty thumps or bangs or smoke or heat etc.
Clue.. the speaker relay had been temperamental earlier in this repair thread and instead of buying a new relay I thoroughly cleaned its contacts (they were grubby and had obviously been cleaned, scratched, during a previous repair.)
All voltages for DC,Idling etc etc have been pot on and stable.
Do my A-1's symptoms suggest that it just needs a new relay? Is there anything else worth checking?
 
Hifibythekg said:
@avionic kindly gave me the exact reference for the replacement,
https://www.mouser.com/ProductDetai...afety/MY2-02-DC12?qs=NHN4o8quFyQ4cbbzu8bEeA==
but I didn't replace it because I couldn't find a UK stockist and Mouser etc had a huge single order/US shipment surcharge otherwise I'd have put a new one in while the old one was off the board.
Farnell have this one but is it correct?
https://uk.farnell.com/omron/my2-12dcs/relay-dpdt-250vac-30vdc-10a/dp/186235?st=my2-02-dc12View attachment 2684537
Click to expand...

I think these are MY2 and not MY2-02 (with pcb terminals). Below is what @avionic posted above, Omron’s data sheets can be very lengthy and confusing at times.

D97EA25E-370D-4094-9A77-0F015608F682.jpeg

Added:
Potentially you could use this through relay sockets but I really really really (did I say really?) don’t recommend that. I did that for a while as an experiment to find out if there were any audio quality difference using different relays but from time to time I was getting intermittent speaker connection or losing one speaker entirely because the relay was not sitting rock solid in the socket. I finally did away with the socket and soldered in the ones I liked best. Just for your reference though, here’s the link to the socket too:
https://uk.farnell.com/omron-indust...ket-pcb-8-pin/dp/1181252?MER=sy-me-pd-mi-acce
 
Last edited:
Thanks @Sparkplug very helpful.
Just before I order a replacement are there any other components or connections that could be faulty and contribute/cause the relay to open?
Or is this ‘random’ activation of the relay the behaviour of an old ‘tired’ relay even one with freshly cleaned contacts.
In all other regards the amplifier is performing beautifully and to spec.
 
Hifibythekg said:
Thanks @Sparkplug very helpful.
Just before I order a replacement are there any other components or connections that could be faulty and contribute/cause the relay to open?
Or is this ‘random’ activation of the relay the behaviour of an old ‘tired’ relay even one with freshly cleaned contacts.
In all other regards the amplifier is performing beautifully and to spec.
Click to expand...

As I’m not a fan of carpet-changing components, no, I can’t think of anything at this time. Since the problem comes and goes, my guess is that you have a physical problem somewhere, a loose solder connection, a temperature dependent cold solder joint, a crack somewhere in pcb that acts up with change in temperature. I suggest doing a complete reflow of all suspect (and maybe non-suspect) solder joints including the RCA connectors. 9 out of 10 the problem with these old amps is physical failure rather than electronic. The old relays got to go.
 
Last edited:
Thanks for your thoughts @Sparkplug
Yes, think I’ll get the relay changed and see if the fault occurs again. If so, as you say, check all the solder and joins. Would do this first but have done it a few times already as part of other fault finding and repairs.
Cheers.
 
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