One bad resistance on my crack [solved]

[robotlover]

Hey Guys,

I finished building my crack a few days ago and seem to have a a problem

All of my resistance checks line up with the manual except one:

terminal 13 should climb steadily to 270K ohm but mine reads out consistently at 520k ohm.

I've checked my soldering, and had someone else check it at well.

Does anyone know what I should try next?

Thanks,

[Paul Birkeland]

Is your 270K resistor soldered across that last 220uF/250V capacitor?  If so, you can move on to voltage checks.

[robotlover]

Yeah, I was thinking that the last resistor was the problem so I re-soldered all of 12 and 13.

Guess I'll move on to voltages!

[robotlover]

Well that didn't last long... blew the fuse right off the bat.

guess it's back to the drawing board...

[Paul Birkeland]

Check the orientation of the UF4007's, and the orientation of the black 220uF/250V caps.

[robotlover]

I think you pointed me in the right direction with those UF4007s,

Looks like once things got a little cramped in there they crossed each other and shorted out a bit.

With any luck I'll be back to checking voltages tomorrow after a trip to the radio shack for some more fuse

Many thanks!

[robotlover]

The good news is that I'm no longer having trouble with fuses.

The bad news is that I am having quite a few bad voltages:

Terminal| My voltages (expected):
1  | 0 (90)
2  | 178 (170)
3  | 0 (0)
4  | 178 (170)
5  | 79 (90)
6  | 0 (0)
7  | 63 (100)
8  | 0 (0)
9  | 106 (100)
10| 0 (0)
11| 0 (0)
12| 0 (0)
13| 178 (170)
14| 0 (0)
15| 197 (185)
20| 0 (0)
21| 218 (206)

A1| 80 (90)
A2| 0 (0)
A3| 1.6 (1.5)
A4| 0 (0)
A5| 0 (0)
A6| 0 (90)
A7| 0 (0)
A8| 0.15 (1.5)
A9| 0 (0)

B1| 0.01 (90)
B2| 179 (170)
B3| 63 (100)
B4| 80 (90)
B5| 179 (170)
B6| 107 (100)
B7| 0 (0)
B8| 0 (0)

LED to A3 Does light up
LED to A8 Does Not light up

And a picture for good measure

http://imgur.com/ODm4Hq4

[Paul Birkeland]

Check the wiring on your 9 pin socket. 

0V at terminal 1 is a very bad sign - this means that a short is present around the nine pin socket, potentially between pins A6 and A7, or maybe between A8 and A7 (since we can tell no current is being drawn through the LED at A8).

-PB

[robotlover]

Right Again!

This time it was a WRONG connection, you can see in the photo that I had mistaken placed the lead from the pot over to A6 and it was supposed to be at A7!

After that everything checked with the exception of my voltages being at about 79 instead of 90. I figure this will either go away as it burns in a bit, or is perhaps the fault of some less-than-perfect soldering somewhere along the line.

I ended up toasting a couple LEDs but I "borrowed" some from my Speedball kit.

Guess I'll have to email and see if I can get them replaced but for now I'm happily listened to my stock crack!

[Paul Birkeland]

The 79V vs. 90V just indicates that your 12AU7 is a bit more potent than what we used originally to measure the voltages. I'm glad you got it up and running, we can send you some extra LED's.