Another Yamaha

[No1baggiesfan]

Re: Another Yamaha

Voltages were checked with the amp turned on.
15v was the DC voltage measured
Q1067/8 both gave 62v to ground
Q1067 tested 7.2v between b/e and b/c with amp off where Q1068 tested 0.45

[R_J]

Re: Another Yamaha

Voltages were checked with the amp turned on.
15v was the DC voltage measured
Q1067/8 both gave 62v to ground
Q1067 tested 7.2v between b/e and b/c with amp off where Q1068 tested 0.45

If you measured 15 volts on CB101 I suspect D1041 could be shorted
You need to measure the voltages on the two regulator ic's ic101 and ic102. check the input and output and note the polarity also.
Q1067/8 both gave 62v to ground ????? this makes no sense at all,
with amp turned on
Q1067 should have positive62 volts on the EMITTER and about Positive 55-60 volts on its collector
Q1068 should have negative62 volts on the COLLECTOR and about 55-60 volts on the emitter.

[No1baggiesfan]

Re: Another Yamaha

IC101 19.3v IN 11.97v OUT 0v com
IC102 -6.5v OUT 18.2v COM 0v IN
Q1067 62v 63v
Q1068 -62.5 -61.6

Sorry, misread my handwriting, left off the minus

[R_J]

Re: Another Yamaha

IC102 is bad, or you are not mesuring it right. It is a negative 12 volt voltage regulator
It should have about -18 volts IN, ground would be 0v and output should be -12v
The pinout between positive and negative are NOT the same.

[No1baggiesfan]

Re: Another Yamaha

[ATTACH]190438[/ATTACH]

I will double check, but that's what I got all measured to ground.

2nd test:
OUT 1v COM -18v IN 0.005v

Getting a relay click when I test the out voltage, it doesn't effect the result tho

[R_J]

Re: Another Yamaha

In that area, There is a plug W110, You can check the voltages on it. you should see +12v, ground, -12v, +18v

[No1baggiesfan]

Re: Another Yamaha

W110 showing:
12v. 0v. -6v. 18v

[R_J]

Re: Another Yamaha

I would say that IC102 (KIA7912P) is defective. Just to be sure your input voltage is ok, check that you have negative -18 volts on C1076 or R1238

[No1baggiesfan]

Re: Another Yamaha

should the voltages of ic334, ic333, ic457 be similar?

Should I take out ic102 and test I out of circuit ?

[R_J]

Re: Another Yamaha

Of course not, they are different voltage regulators (see schematic) IC334 +5 volt 4 pin regulator. IC457 3pin +5 volt regulator, again not the same.
How would you check ic102 out of circuit? do you have an adjustable bench power supply?
Look at the data sheet for a kia7912 and you will see what is inside.

[No1baggiesfan]

Re: Another Yamaha

C1076 18.75v
R1238 1.4v

It was a suggestion from someone else, as they were 5v regulators.

[R_J]

Re: Another Yamaha

You should be getting NEGATIVE 18.75 on C1076, and R1238 is connected directly to C1076 so how do you get a different voltage on it?
You should have -18 volts on both sides of R1238

[No1baggiesfan]

Re: Another Yamaha

I tested across each, sorry, it was -18 ffs
Ok, each to ground:
C1076 -18.74
R1238 -18.77 and -20v other side

[R_J]

Re: Another Yamaha

Ok, that's better. I just wanted to be sure R1238 was ok.
Here is what is inside of that negative voltage regulator ic.
I am sure the ic is bad, If there was something loading the -12 volt line I suspect the voltage would be 0 and not -6volts

[No1baggiesfan]

Re: Another Yamaha

I guess the next step is to replace it and see what happens ? Or is there more to check ?

Quite a lot going on inside there, it's more complex than I expected

[R_J]

Re: Another Yamaha

Yes, replace it, be sure to get a 12 volt negative regulator 7912

[No1baggiesfan]

Re: Another Yamaha

Having trouble finding those here in the U.K. ��
Does it have to be an exact KIA7912P or can it just be a 7912 negative 12v TO-220 ?

[R_J]

Re: Another Yamaha

It is an all plastic case, correct?

It does'nt need to be a KIA any xx7912 should be ok, It is a total plastic case to220, so you should replace it with the same type. Most to220 have the metal tab exposed so when monuted it would short to the heatsink
The tab is connected to the input pin so it must be isolated from the heatsink

[No1baggiesfan]

Re: Another Yamaha

Ok, thank you very much for your help and your time R_J you are a legend.
I will now go and shop lol, I will update when I get it installed

Thank you

[R_J]

Re: Another Yamaha

I hope it does fix it, I can't really see anything else that would cause the problem.