New Crack - resistance checks

[rs01]

Hi everyone,

I built my new Crack kit in a whirlwind last night, but I think I may have damaged a capacitor in the process by nicking it with the iron (there's a little melted bit on the edge where the iron touched) - when I measure terminal 13, the resistance climbs to around 36K ohms then zeros out.  Is a damaged capacitor a reasonable assumption and if so, could anyone point me in the right direction for obtaining a replacement from Mouser or similar?

Thanks,

Ryan

[Grainger49]

Ryan,

How does the capacitor in the other channel measure.  I.E. does it climb and go to zero?  Is it possible it climbs and goes OL, for overload?  That is what is expected, an overload reading.

[rs01]

Grainger,

Actually it does go to OL - it climbs to around 36K ohm then reads OL, thanks, in my excitement I forgot how to read  .

[Grainger49]

Then on to the voltage checks.

[rs01]

I'm a bit confused by these, nearly everything is wrong, expected is black, read values is well, red:

1: 90 -.696
2: 170 -.684
3: 0 0
4: 170 -.951
5: 90 -.953
6: 0 0
7: 100 7
8: 0 0
9: 100 .60
10: 0 0
11: 0 0
12: 0 0
13: 170-.679
14: 0 0
15: 185 -.681
20: 0 0
21: 206 236.5

A1: 90 -.948
A2: 0 0
A3: 1.5 .66
A4: 0 0
A5: 0 0
A6: 90 -.694
A7: 0 0
A8: 1.5 .628
A9: 0 0

B1: 90 -.695
B2: 170 -.685
B3: 100 6.6
B4: 90 -.949
B5: 170 -.686
B6: 100 .9
B7: 0 0
B8: 0 0

On a small positive note, the tubes light and glow.

[Doc B.]

Off the top of my head I'd say the problem is somewhere between terminal 21 and terminal 15

[Paul Birkeland]

Off the top of my head I'd say the problem is somewhere between terminal 21 and terminal 15

Yes, I'd be more specific and say the 270 Ohm resistor that sits between them is missing or not connected

[Doc B.]

See, you get even better info when the guy who designed it steps in. In 1998 I knew every terminal and every part attached to it in every kit we made, right off the top of my head. 15 years later I am really glad that PJ, PB, Josh and the forum members have the patience to get into the manual and suss out the terminals. That part of my brain seems to have died from years of overload. And unfortunately that part seems to have been reassigned to the storage of my guitar playing skills...

[rs01]

Off the top of my head I'd say the problem is somewhere between terminal 21 and terminal 15

Yes, I'd be more specific and say the 270 Ohm resistor that sits between them is missing or not connected

Paul,

Thanks - it is there (assuming you're talking about the one between 21U and 15U), but I'll double check and re-flow the solder tonight when I get home.  Thanks a ton to everyone for all the help so far, it is hugely appreciated!

[Grainger49]

It is easy to check for continuity.  Measure resistance from the bottom holes in the terminal strips.  The resistor should be in the top holes.  

[Paul Birkeland]

I'd also measure the resistance of that resistor.  You can do this while it's in the circuit (but powered down please) by putting a meter probe on either side of the resistor.

The high voltage on one side of that resistor tells me that pretty much no current is making it through the power supply, so there may be lingering voltage at 21U.  If you google "bleeding high voltage supply", you can get some info on handling this situation.

-PB

[rs01]

I'd also measure the resistance of that resistor.  You can do this while it's in the circuit (but powered down please) by putting a meter probe on either side of the resistor.

The high voltage on one side of that resistor tells me that pretty much no current is making it through the power supply, so there may be lingering voltage at 21U.  If you google "bleeding high voltage supply", you can get some info on handling this situation.

-PB

I took the advice on http://www.expertsmind.com/topic/resistors/bleeding-off-charge-9609.aspx - which resulted in a loud crack and a spark from the cap on 20 and 21, so it certainly seems like it's not bleeding through the resistor.  My meter is reading "OL" with probes on either side of the resistor.

http://imgur.com/Gnqrxhn

Is it worth de-soldering both sides and re-attaching everything?

Thanks,

Ryan

[Grainger49]

Once the circuit is complete there is a "bleeder" resistor at the final capacitor.  That is the one that is horizontal in your picture. 

Now it seems that the power supply resistor is bad.  It should not read open (overload).  I don't see that reattaching it will bring it back to life.  It should be burned or otherwise damaged to be open.  You will need to remove and replace it.  Give it a good look when you remove it.

[rs01]

Once the circuit is complete there is a "bleeder" resistor at the final capacitor.  That is the one that is horizontal in your picture. 

Now it seems that the power supply resistor is bad.  It should not read open (overload).  I don't see that reattaching it will bring it back to life.  It should be burned or otherwise damaged to be open.  You will need to remove and replace it.  Give it a good look when you remove it.

I pulled it out and there appears to be no damage at all, or at the least no burn marks.  The underside is a bit uneven, but that seems to be normal from looking at the other similar style resistors.  Through some Googling, it looks like the part number is SQP500JB-270R for Yageo, is that correct? 

Also, have I potentially put any other components at risk with having the resistor open and the amp powered on?

Thanks,

Ryan

[Grainger49]

Ryan,

Since it looks OK measure the resistance out of the circuit.  Yes, others might have been damaged too but let's see if the resistor is bad then move on to the capacitors that would have been molested too.

There should be another resistor between the two caps on the left side of the transformer.  Does it measure as it should?  Again, just measure resistance across it with the amp off.