clinic-audio
all on YAMAHA untill 1990
Great speed for research , Dave !
Yamaha B2 driver board diagnosis
- Thread starter belgianbrain
- Start date
belgianbrain
Super Member
Thanks for the tips guys.
On another note, schematic of driver board says R153 should be 33K. For both of my driver boards R153 measures ~18K.
Is this a typo on the schematic?
On another note, schematic of driver board says R153 should be 33K. For both of my driver boards R153 measures ~18K.
Is this a typo on the schematic?
In circuit or out?
Don't have a B-2 handy at the moment.
belgianbrain
Super Member
In circuit or out?
Measured out of circuit, of course.
It basically measured the same in circuit too, though.
Does it look OEM ? Are there any markings on the resistor? Could be a typo. What does the parts list call for?Measured out of circuit, of course.
belgianbrain
Super Member
It looks original. It has coloured stripes on it like all the others, but they're getting faded to read with certainty. The parts list in the SM is not exhaustive - doesn't list to that detail, does it? I don't see many resistors on the list, just the fusibles and a few metal films.
belgianbrain
Super Member
Found a bad 2SC1775A.
I think I'm going to replace all transistors just for peace of mind. I already did TR107-110 and TR121-124.
Does anyone have suggested equivalents for:
2SA872A
2SA872BV
2SC1775A
2SC1775BV
2SC1439B
2SC734Y
2SA561O
2SA858V
I think I'm going to replace all transistors just for peace of mind. I already did TR107-110 and TR121-124.
Does anyone have suggested equivalents for:
2SA872A
2SA872BV
2SC1775A
2SC1775BV
2SC1439B
2SC734Y
2SA561O
2SA858V
clinic-audio
all on YAMAHA untill 1990
Hello
I think I'm going to replace all transistors just for peace of mind.
I will not do it at your place , this is not necessary . Just replace bad components
I think I'm going to replace all transistors just for peace of mind.
I will not do it at your place , this is not necessary . Just replace bad components
clinic-audio
all on YAMAHA untill 1990
To answer to your questionR153 is 33K on schematic
R153 is not listed in parts list
R153 is 18K on all the driver boards I have (more than 14 pieces )
If you watch carefully in SM the orange 100nF capacitor next to R153 is symbolised by a " strap" ......
Many mistake in service manual
not enough time to list them all here
View attachment 1328630
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belgianbrain
Super Member
Thank you, sir.
The reason I suggest changing transistors: I have two boards not functioning quite right. The first one balances fine but wants to adjust between +/- 5 and +/- 8 volts for PG and NG. The second one has more of a challenge with balance, and wants to adjust between about 26V and 40V PG and much, much lower on NG.
I have tested all resistors, capacitors, and diodes twice on both boards and everything looks good. But, I do not have a curve tracer. I can only do basic DMM test on transistors. At one point, I tried moving TR 119 and 120 from second board to first board and suddenly I could adjust first board to perfect +/- 13.5V. Then I had my probe adventure and we are back to +/- 6V.
I have one bad 2SC1775A and I'm quite sure there are more transistors that are passing DMM test but are still not functioning properly.
clinic-audio
all on YAMAHA untill 1990
Original B2 transistors are really rare and deserve to be replaced only if they fail
You can send your boards to somebody who knows very well B2 " Vint Age " he is like you in Canada
I am in France and shipping charges will be more expensive
You can send your boards to somebody who knows very well B2 " Vint Age " he is like you in Canada
I am in France and shipping charges will be more expensive
belgianbrain
Super Member
Are you saying equivalent transistors for most of the transistors on the B2 driver boards are not available?
clinic-audio
all on YAMAHA untill 1990
no , original transistors are difficult to find
I don't talk about substitutes
I don't talk about substitutes
belgianbrain
Super Member
I was tinkering with a driver board today. It balances to 0V just fine and gives me an even +/- 21V at PG and NG. BUT, VR102 has absolutely no effect on changing PG and NG. And yes, VR102 is working.
Thoughts?
Thoughts?
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belgianbrain
Super Member
So, to recap: all passive components on this driver board have been checked and verified.
It now has brand new replacements for all TR117 -> TR124.
I'm still at the situation where it balances to 0V just fine and gives me an even +/- 21V at PG and NG, but VR102 has absolutely no effect on changing PG and NG.
Does bias adjustment rely on something else that I'm missing?
It now has brand new replacements for all TR117 -> TR124.
I'm still at the situation where it balances to 0V just fine and gives me an even +/- 21V at PG and NG, but VR102 has absolutely no effect on changing PG and NG.
Does bias adjustment rely on something else that I'm missing?
Does the other board adjust per manual?
belgianbrain
Super Member
Not yet! They both have issues, and I'm tackling them one at a time.
Interesting observation: VR102 didn't adjust anything because my dyslexia kicked in and I installed R153 back in the wrong position - the only position on the board that has an unused resistor spot.
So, what is interesting is that without R153 installed I get a balanced +/- 21V for PG and NG.
Once I reinstall R153, I can get PG to +15V but NG hovers around 0.
What base voltage are you seeing on TR123 and 124? What transistor part number is TR123? 124?
belgianbrain
Super Member
R124 base is about -0.9V. R123 base is about .75V.
Parts are Toshiba TTC004B and TTA004B.
Parts are Toshiba TTC004B and TTA004B.
