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Yamaha A1 restoration 2021

Hifibythekg said:
Thanks Nashou, glad you mentioned. The battery isn’t new any more, and it recently showed a one-off battery image. I’ll try to get a new one v soon.
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I wouldn't trust the reading from your DMM if the battery is weak. Get new one before using it for any voltage readings especially.

And some resistance reading need to have one leg lifted , as it might be parallel or in series with another component unless you verified in it with the schematic .

Athanasios
 
Hifibythekg said:
I tried to measure the little white fusistors between the small heatsinks but the measurements are all over the place going up and down while the test leads are connected.
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Needs to be isolated from the circuit. Sounds like it is back feeding through a capacitor.
 
Thanks for the advice Nashou, I didn't realise.
I've now inserted a brand new battery and all the readings and meter behaviour are virtually identical.

So, getting down to replacing components would the following plan seem fairly rational.
Order and replace:
5W 0.47 ohm resistors (x2)

Anything else?
How about the two brown resistors at R104 and R102, is there anything that would better match R101 and R103 that look to be original?

Replace trimpots with Bourns.

Also check the the 68 ohm fusistors if they test bad with lifted legs.

Insert all these and see how the new pots behave ?
 
One pot is working already, you don't know the other one isn't working yet. If you do change the trimpots, when you take them out , measure their resistance (setting) and preset the new one to as close as you can before installing.

Not that it's been proven yet they need replacing.
 
Good point Martin. Agreed, I did the same sort of thing on my NAD 3020. And, yes, that pot may not be faulty.
But the essential changes to get started on testing appears to be only the ones I suggested above?
The original R102 and 104 are listed in the service manual as carbon resistors and they’re all blue. Being a novice are the replacements on the other side, brown, likely to be different?
 
Yes, that’s what I thought, but in the SM those locations are listed as carbon resistors, even though the originals are blue.. oh well.
 
Hifibythekg said:
Yes, that’s what I thought, but in the SM those locations are listed as carbon resistors, even though the originals are blue.. oh well.
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Carbon or metal film.. Machs nicht both will get the job done. Metal is suppose to be " quieter " than carbon film ..
 
Just awaiting arrival of some components get this A-1 to the next, hopefully final, stage of repair.
Thanks to all for your help so far.

Would like to have the same type of resistors on both channels in location
Can anyone tell me the correct spec for these?
R 101,102, 103m 104.
Service Manual says they’re “Carbon 330ohms” but to order I need to know what are the additional specs?
Which:
-power rating?
-resistance tolerance?
-voltage rating?

Am also seeking help on a simple cheap way of using a 70W dummy load to set the bias and offset if anyone can help?
 
Hifibythekg said:
Am also seeking help on a simple cheap way of using a 70W dummy load to set the bias and offset if anyone can help?
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I never use a dummy load to set offset or bias... No input, volume at min. and no load. and no dim bulb.
 
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