Re: New Crack Build Voltage Problem [resolved]

mbundock · **on:** February 05, 2021, 02:06:13 PM

I have too high voltages on terminal 5 and 9, in the 140. volts.
and one LED does not light up, the one between A3 and central pin.

the rest is all fine.

mbundock · **Reply #1 on:** February 05, 2021, 02:10:34 PM

I just finished the Crack.
resistance tests were perfect.

But problems with voltages .
I have a high voltage on terminal 5 and 9. Around 140 V.

and the LED between A3 and central pin does not lit up.

Paul Birkeland · **Reply #2 on:** February 05, 2021, 03:14:19 PM

Do both halves of the 12AU7 light up? If the solder joint at A4 and A5 is dodgy and only half of the 12AU7 is lighting up, that will cause the problem you have.

If you're 100% certain both halves of the 12AU7 are illuminated, can you carefully measure the voltage at A3?

For most instances like this, we find that builders will zero in on the LED itself and resolder it until they destroy it, so resist the temptation to go nuts resoldering the LED itself.

mbundock · **Reply #3 on:** February 06, 2021, 06:06:01 AM

Thanks for the answers.

The 12AU7 works fine. And I tried with another tube and the results are the same.

This morning the LED between A8 and central stopped to lit.
The other one is still off.

it is my fifth Crack that I build and I never had any problems of that sort with the 4 precedent ones.

Here are all my measurements.
A1-0
A2-0
A3-0
A4-8 V
A5-0
A6-87V
A7-0
A8-2V
A9-0

B1-86
B2-163
B3-108
B4-146
B5-160
B6-146
B7-0
B8-0

T1-86V
T2-163
T3-0
T4-163
T5-147
T6-0
T7-107
T8-0
T9-146
T10-0
T11-
T12-
T13-163V
T14-0
T15-186
T18-77
T19-78
T20-0
T21-211
T21-211

Paul Birkeland · **Reply #4 on:** February 06, 2021, 06:12:59 AM

A1 being 0V would indicate either a measurement error or some kind of short.

I would also guess you don't have an autoranging meter, as A8 should be more like 1.5V rather than 2V.

0V at A1 and 0V at A3 but 146V at B4 is not a possible set of voltages. A1 wires to terminal 5, terminal 5 wires to B4. You either have made a measurement error or you have a wiring error. It might help to post some build photos.

mbundock · **Reply #5 on:** February 06, 2021, 09:32:09 AM

Previously, there was a bad connection between A1 and 5U that was corrected. Now the two DEL lit up ,

but the resistors are very hot and there is 170 V on T3.

Did I blow the resistors ?

Paul Birkeland · **Reply #6 on:** February 06, 2021, 09:52:09 AM

If you are getting 170V on terminal 3, which is connected to the chassis, then you have a loose black wire in your amp. The most common place I find them when doing repairs is where the two black wires meet on the headphone jack. I would reflow every solder joint in your amp where there is a black wire other than the center post of the 9 pin socket and the power switch.

mbundock · **Reply #7 on:** February 06, 2021, 11:39:02 AM

Problem solved !

You were right. I resoldered a few black joints and all measurements are perfect now.

So is the sound in my Sundara, listening to Thievery Corporation..

Thanks !!!