Another Yamaha

[R_J]

Re: Another Yamaha

Thats strange? what are the voltages on the input. It was an all plastic 7912 correct?

[No1baggiesfan]

Re: Another Yamaha

Getting
0.9v 0.6 and -0.02v off the new 7912

[No1baggiesfan]

Re: Another Yamaha

Weired, I now have 8-10v on the chassis with just the negative lead on it, getting 0v on the new 7912

[R_J]

Re: Another Yamaha

O.k.You DO need that -12volts, so it might be a pain to trace the fault , but it is starting to look like a bad op amp ic?
After closer inspection that -12 goes to quite a few places

[No1baggiesfan]

Re: Another Yamaha

Wife's taxi, lol, I will have a look in the next hour, ty R_J

[R_J]

Re: Another Yamaha

So what is the voltage on the 7912 now? If it is still low there must be something loading it down. or it could be the cap (C1088) on its output is bad.
-12 volts supplies VIDEO (10) board, unplug CB383 and see if the -12v comes up.
-12 also supplies one side of the relays on (page 141)
The -12 also goes to the op amp ic's on (page 137) and elswhere

[No1baggiesfan]

Re: Another Yamaha

Installed new 7912, still no joy ��
PS value still fluctuating but not as bad: 129-135/129
Still getting ps prt 135 h error
Still no standby led

[No1baggiesfan]

Re: Another Yamaha

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

I hope so too lol 👍🏼

https://uk.rs-online.com/mobile/amp/...ators/6869748/
Min order is 10 but free shipping, mouser wanted £5 to ship 1, crazy.

[R_J]

Re: Another Yamaha

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

[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

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

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

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

[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

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 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

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

C1076 18.75v
R1238 1.4v

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

[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

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

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