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Yamaha A1 restoration 2021

That's not really your problem (the switch) anymore, I suspect. The Driver circuit board is very unhappy. I suspect you have blown some transistors.
 
So with this reading does it suggest that both transformers are functioning ok?

Is my problem most likely on the
- power circuit board?
or
- the electrolytic capacitor circuit board?
 
the "Drive Circuit Board" has TP1, TP2, TP3

index.php


the "Electrolytic Capacitor Board" has TP1, TP2, TP3, TP4

index.php


index.php


I don't see any test points on the "Power Circuit Board"...

index.php
 
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On the power circuit board, there looks like maybe an unlabelled Test Point just to the right of the VR201 trim-pot?

I do not know why the voltage ranges are +35V ± 1v and -35V ± 0.5V if there's only one test point.
 
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Martin.Ca said:
On the power circuit board, there looks like maybe an unlabelled Test Point just to the right of the VR201 trim-pot?

I do not know why the voltage ranges are +35V ± 1v and -35V ± 0.5V if there's only one test point.
Click to expand...

This is the Power board , the two pins at the top left are the test points , one is +35 the other should be -35 IIRC . I did this in 2016 or 17 I think.
25946033992_8333f013b0_h.jpg



Here is a pic of the drive board, click pic for full size.

25775814403_65522d7a23_k.jpg
 
Hi Nashou66.
Yes, your photo of the power board shows the two TP on the top left (which, like mine, actually are without labels saying TP1 and TP2, just...’TP.’)
 
Good news.
Audio through both speakers and green Speaker light operating. Speaker switch now serves to switch audio on speakers off and on.
Solution was applying some more Kontact40 onto the Speaker push switch and multiple workings on and off. Let’s say a hundred times.
So, to be clear, for power supply voltage one reads the contacts at 'TP' on the power board by putting one DMM lead on each of the contacts. Maybe by just swapping the leads over one then gets the two readings of +35V, then -35V.
Correct?
Nashou66, do you happen to know the part number for that Bourns that you installed, and does it work perfectly in that location.
The service manual doesn't actually mention adjusting that pot to adjust the voltage, so is it ok to do so?
 
Adjusting Idling Current.
Positive and negative leads applied to contacts as per the diagram in the service manual.
(Neg to TP1, Pos to TP3. Then Neg to TP2 Pos to TP4)
But I get a reading of -2.4mV, and -4.8mV. Turning up the volume increases these figures but increasingly Negative, -6mV, then -8mV.
What does this mean? Should the leads be reversed? Usually increasing the load leads to a positive rise in idling current.
Can tell that all these pots, as ever, are worn/grubby, can anyone recommend the perfect Bourns replacements?
But at least it's all working now, just want to have these currents well-adjusted and stable.
Thanks again for all the help and input so far.
 
Hifibythekg said:
Good news.
Audio through both speakers and green Speaker light operating. Speaker switch now serves to switch audio on speakers off and on.
Solution was applying some more Kontact40 onto the Speaker push switch and multiple workings on and off. Let’s say a hundred times.
So, to be clear, for power supply voltage one reads the contacts at 'TP' on the power board by putting one DMM lead on each of the contacts. Maybe by just swapping the leads over one then gets the two readings of +35V, then -35V.
Correct?
Nashou66, do you happen to know the part number for that Bourns that you installed, and does it work perfectly in that location.
The service manual doesn't actually mention adjusting that pot to adjust the voltage, so is it ok to do so?
Click to expand...

I think others are suggesting to on the "power board" put the DMM -ve lead to the chassis or a Earth, and then test the two TP test points with the +ve DMM lead. That's what I think others were saying. the manual is clearly not clear about what to do.
 
Hifibythekg said:
Adjusting Idling Current.
Positive and negative leads applied to contacts as per the diagram in the service manual.
(Neg to TP1, Pos to TP3. Then Neg to TP2 Pos to TP4)
But I get a reading of -2.4mV, and -4.8mV. Turning up the volume increases these figures but increasingly Negative, -6mV, then -8mV.
What does this mean? Should the leads be reversed? Usually increasing the load leads to a positive rise in idling current.
Can tell that all these pots, as ever, are worn/grubby, can anyone recommend the perfect Bourns replacements?
But at least it's all working now, just want to have these currents well-adjusted and stable.
Thanks again for all the help and input so far.
Click to expand...


Idling current should be independent of Volume setting. If you put the -ve DMM lead to the TP1 & TP2 , I'm not sure why you're getting negative readings.
 
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Hifibythekg said:
Turning up the volume increases these figures
Click to expand...
Volume to be set to minimum as per SM, leave it alone

Hifibythekg said:
increases these figures but increasingly Negative, -6mV, then -8mV.
What does this mean? Should the leads be reversed?
Click to expand...
Are you adjusting VR101,2 as per the SM, don't be overly concerned about the voltage polarity, it just means a slight shift in the
bias voltage (at base of npn output), the absolute value is what's important.

Hifibythekg said:
can anyone recommend the perfect Bourns replacements?
Click to expand...
I used 3296Y series, 1k ohm, you will need to bend pins to fit.
 
Thanks again guys.

So, the amp plays very, very nicely already on some small test speakers.
The Idling Current.. with the original trimpots in place reads:
TP4 to TP2 with negative lead on TP2, I can dial in -7.4mV perfectly, and very stable.
TP1 to TP3 reads -0.8mv and rotating the trimpots back and forth has no effect whatsoever.
Volume throughout these adjustments is at zero. (Although, if I do raise volume, then the idle current reading increases too.)

Question: Is the inability to change the TP1 to TP3 idle current caused by a worn or faulty trimpot, or could it be anything else?
 
Hifibythekg said:
Question: Is the inability to change the TP1 to TP3 idle current caused by a worn or faulty trimpot, or could it be anything else?
Click to expand...
Measure dc voltage at O+, black probe connected to GND, repeat for I+
While monitoring the O+ voltage adjust the trimpot, does voltage change, adjust for 1-1.2V at O+
Does your unit have the 4 "bias transistors" TR137,8,9,149?
upload_2021-9-27_6-58-43.png
 
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