Crack finish. Volts problems.

[michael30]

Hello everyone
I finished the crack and checked the volts.
First of all,one of the LEDs do not light up.
These are the test results:
terminals-
1:  157.6
2:  173.7
3:  0
4:  174.5
5:  86.6

6:  0
7:  159
8:  0
9:  112.2
10:  0

I over checked all the wiring.. looks good.
i'm new so i can't point at the problem.
Ty for help!

 

[Paul Birkeland]

Do you see both sides of the 12AU7 glowing?

Can you very carefully check the voltage on A8?

Generally this is not related to the LED itself, so resist the urge to reflow the solder joints around the LED, as excess heat can damage them.

 

[Paul Birkeland]

Yes, 12U is OK as a ground.  Terminals 1 and 7 will fall into line based on the information we find from the voltage measurement at terminal A8.

 

[michael30]

A8 Voltage is 18.57.
I deleted the comment before by a mistake.

 

[Paul Birkeland]

That is generally indicative that the LED has been cooked and is no longer working.  You can connect a piece of wire between A3 and A8, then in all likelihood you will find that your voltages are proper.

 

[michael30]

Ok I did as u said.
Terminal 1 read: 86.6V
Terminal 2 read: 112.6V.

I will order a new led.

 

[michael30]

I just found a replacement HLMP-6000 LED in my garage.
it doesn't have banded side like yours.. Can i use it?

 

[Paul Birkeland]

If you can't tell which end is the cathode, it's not a good idea.  They also absorb moisture over time, and a garage is pretty humid.

112V is still a little high, what DC voltage do you see at A7?

 

[michael30]

If you can't tell which end is the cathode, it's not a good idea.  They also absorb moisture over time, and a garage is pretty humid.

112V is still a little high, what DC voltage do you see at A7?

Btw i meant Terminal 7.. but you got me.
anyway i read 0 for A7.

https://postimg.cc/jCSgK6tR

 

[Paul Birkeland]

I would reflow A5 a bit. 

Can you list your voltages on terminals 1-10 again as the amp is now?

-PB

 

[michael30]

Thank you for fast respond.
The new reads:
1)  85.7
2)  179.4
3)  0
4)  179.4
5)  89

6)  0
7)  111.6
8)  0
9)  114.6
10)  0

Both LEDs glowing. https://i.postimg.cc/wTTy1ZCT/IMG-9761.jpg

 

[Paul Birkeland]

That's a working amp.

 

[michael30]

Cool, Thanks!
Can I run it for now with the wire A3-A8 until the new LEDs will arrive?

 

[Paul Birkeland]

You can run it with the wire there forever if you'd like.

 

[michael30]

Update Voltages after soldering wire a3-a8.

1) 85

2) 184
3)0
4)184
5) 0

6)0
7)113.5
8)0
9)116
10) 0

after soldering reasults.

 

[Paul Birkeland]

The 0V at terminal 5 looks unlikely based on the other voltages, can you double check?

 

[michael30]

after 30 min run.
terminals:

1)86.8
2)174
3)0
4)174
5)89.5

6)0
7)110.4
8)0
9)112.5
10)0

Yesterday i checked it with 235v.. now im at my brother house and i get around 223v from the wall.
Also I think can hear diff in volume between left and right ( left +1 -2).  not sure yet.

 

[Paul Birkeland]

Those are working voltages.  You can check the Crack FAQ stickied on this board regarding channel imbalance at low levels on the volume pot.  It's not abnormal and there's an easy modification to fix that. 

-PB

 

[michael30]

Hey Paul .
Just wandering... I wasn’t able to touch the chassis because it gets really hot, is that normal for the crack ? I only using 1/10 of the volume right now.. after 2 min I can’t touch it.

 

[Paul Birkeland]

If the voltages in your amp are normal, then the temperature of the top plate is normal (provided you have also installed the rubber feet).

A stock Crack will produce some extra heat in the top plate around where the 3K/10W resistors are and the Speedballed Crack will produce slightly more heat overall under the plate, but less localized.