Yamaha B-2 restoration journey

Thanks to all contributors of this amazing thread, I am working on a recently purchased B2 and I am finding so much useful information here.

Regarding the service manual, I found a very nice PDF version on www.manualslib.com, which comes in color and in high definition (~20Mb download), much better than the other available on hifiengine & co.
 
hi Gang, quick question regarding the B-2 driver boards, respectively the R147, R149 voltage divider:
On a US model that I have, with a later, 10k+ serial number, the actual resistors are 1k each, an even split. On the older <3k serial number units from Japan On at least two of them, the R values match the schematic (R147 =1.5k, R149 =470R)
is anyone aware of a service bulletin that accounts for this change in later models?
boards numbers are different as well
Older: NA06747
Newer: NA06811

is anyone nere aware of this change, or has noted the different (from schematic) value resistors?

@Oilmaster would you happen to be aware of this change?
 
Last edited:
Thanks to all contributors of this amazing thread, I am working on a recently purchased B2 and I am finding so much useful information here.

Regarding the service manual, I found a very nice PDF version on www.manualslib.com, which comes in color and in high definition (~20Mb download), much better than the other available on hifiengine & co.
hi Spagetti, what serial number is your unit and would you please look at R147 and R149 when you are doing the driver boards? Also, is your unit US, EU or Japan?
 
hi Gang, quick question regarding the B-2 driver boards, respectively the R147, R149 voltage divider:
On a US model that I have, with a later, 10k+ serial number, the actual resistors are 1k each, an even split. On the older <3k serial number units from Japan On at least two of them, the R values match the schematic (R147 =1.5k, R149 =470R)
is anyone aware of a service bulletin that accounts for this change in later models?
boards numbers are different as well
Older: NA06747
Newer: NA06811

is anyone nere aware of this change, or has noted the different (from schematic) value resistors?

I don't think it's a big deal all together.

1) During normal operation it does not impact the bias circuit's current or voltage values, as the voltage dividier is not active while the total resistance sum remains the same. (in fact, it's not a voltage divider)

2) During start-up, when the +/-B2 power rails turn on later than the +/-B rails, then there is a minor impact due to the fact the bias circuit (fed via D112/113), since the series resistance from rail to rail will be 1kOhm higher, though that is relatively irrelevant due to R153 (33K) and VR102 (100K max) which dominate by far the DC resistance in that loop.

Frankly, the purpose/benefit of that mod escapes me.
 
hi Spagetti, what serial number is your unit and would you please look at R147 and R149 when you are doing the driver boards? Also, is your unit US, EU or Japan?

@rottalpha right now I can't do that, I'll be back home on friday evening then I'll let you know for sure. I think my serial number is in the range of 4XXX, but I may be wrong, the SN I have in mind could be from my Sansui BA-F1 I've been working on recently...
 
I don't think it's a big deal all together.

1) During normal operation it does not impact the bias circuit's current or voltage values, as the voltage dividier is not active while the total resistance sum remains the same. (in fact, it's not a voltage divider)

2) During start-up, when the +/-B2 power rails turn on later than the +/-B rails, then there is a minor impact due to the fact the bias circuit (fed via D112/113), since the series resistance from rail to rail will be 1kOhm higher, though that is relatively irrelevant due to R153 (33K) and VR102 (100K max) which dominate by far the DC resistance in that loop.

Frankly, the purpose/benefit of that mod escapes me.
Thank you Sir!
It looked like a voltage divider to me, but yes the sum of total resistance is the same.
 
hi Gang, quick question regarding the B-2 driver boards, respectively the R147, R149 voltage divider:
On a US model that I have, with a later, 10k+ serial number, the actual resistors are 1k each, an even split. On the older <3k serial number units from Japan On at least two of them, the R values match the schematic (R147 =1.5k, R149 =470R)
is anyone aware of a service bulletin that accounts for this change in later models?
boards numbers are different as well
Older: NA06747
Newer: NA06811

is anyone nere aware of this change, or has noted the different (from schematic) value resistors?

@Oilmaster would you happen to be aware of this change?
In my European B-2 with serial no. 4027 the color codes of those resistors are as follows (R147 on top):

Capture.JPG
 
In my European B-2 with serial no. 4027 the color codes of those resistors are as follows (R147 on top):

View attachment 1080395
Thank you!

out of curiosity, what is the board model number for yours?

I asked the question, but I think I can answer it for myself...I do have a high serial number (>9000) Japan unit. The US unit is >10000. I just need to pop the hood on the Japan unit.
 
Thank you!

out of curiosity, what is the board model number for yours?

I asked the question, but I think I can answer it for myself...I do have a high serial number (>9000) Japan unit. The US unit is >10000. I just need to pop the hood on the Japan unit.

Capture.JPG
 
yep, same board version as the Japan, early serial number boards I have. So It is based on early vs later unit serial numbers rather than the market region.
your unit has the blue heatsinks, correct?
Yes, the blue ones. I will never forget: no silpads and no mica plates, just thermal paste :D
 
Back
Top Bottom