j99 voltage off at pin5, possible broken R28????

[yavuz]

I had 2XC84s finished but power up check failed.
Waiting for an answer for what to do on those....
So, I moved onto my 2 X J99s.

I was soooo careful with every step.
I could swear that everything is correct.
However, I have failed at the initial power-up test.
I put negative probe on the Pin4 of U1 and voltage between Pin4 and Pin3 reads 14.45 which is what it should nearly be.
Right?

However, without moving negative probe from Pin4, I move the positive probe to Pin5 and DMM reads 00.4 instead of negative -14.5V.
Why????

Onething I noticed is that R28 keeps turning counter clockwise w/o making any soft click. The other regulator R32 seems fine meaning it makes the soft click....

What could be causing this?????

[tpryan]

However, without moving negative probe from Pin4, I move the positive probe to Pin5 and DMM reads 00.4 instead of negative -14.5V.

With the negative meter probe at J7, pin 2 (second from the front), what voltage do you measure at the negative side of C16? At the cathode (banded end) of D8? And at J7, pin 3? Is U5 getting hot?

Onething I noticed is that R28 keeps turning counter clockwise w/o making any soft click.

Sometimes they don't click. That's why the directions say 25 turns or until you hear a click.

[yavuz]

With the negative meter probe at J7, pin 2 (second from the front), what voltage do you measure at the negative side of C16?.

-29.8V

At the cathode (banded end) of D8?

0.04 (I think...not sure since can not see under the diode)

And at J7, pin 3?

-30.0V

Is U5 getting hot?

No...

[tpryan]

With the negative probe in the same spot as before, carefully measure the voltage at U5, pin 3. Be very careful to not short pins 2 and 3 together, or to short pin 3 to ground.

[yavuz]

0.40V

[tpryan]

With the same care, measure the voltage at U5, pin 2. It should be the same as what you measured at C16.

[yavuz]

No, it's different.

It reads 0.02V...

[tpryan]

Reflow the solder joints at C16 and U5. If you still don't get the right voltages, you'll have to send it back.

[yavuz]

Reflow the solder joints at C16 and U5. If you still don't get the right voltages, you'll have to send it back.

Done that and that fixed it!!!!
Yes....


Off to checking them out.
Now, I have only 1 non-working C84KF left.
I am hoping it is very simple to fix...

[tpryan]

OK, good job. You should probably examine the rest of the board for poor solder joints as well. A bright light and a magnifying glass can help.

[Category 5]

I can't strees strongly enough how much easier it is to get consistent solder joints with eutectic solder (63/37) instead of 60/40 btw.

Eutectic has no plastic phase and seems to have a lower melting temp. It is FAR easier to work with by my experience.

[yavuz]

I can't strees strongly enough how much easier it is to get consistent solder joints with eutectic solder (63/37) instead of 60/40 btw.

That is what I am using.

However, you know how it is...
Late night... Tiredness force you make mistakes...

Also on C84s.... Soo many resistors.
You have to measure each of them etc...

J99s were a lot easier to build for me compared to C84s.
C84s may not be hard either but it requires continous attention and weares you down.