Resistance question

[BZ58]

Crack was sounding great. Shouldn't have messed with it when it worked.

Decided to remove the speedball and save it to reinstall later. I’ve read that all I needed to do is remove small board, replace the two 22.1K resistors, and it will be back to stock. So this is what I did, but when doing resistance checks, I have found values of 0 at OB and OA on the large board. They should read very high, as it says in the manual.  I also checked terminal 7 and 9, and they read 0. Checked the RCA jacks, and they read 0.

Is it possible that my 22.1K resistors are damaged? Are the resistance checkpoints the same with the same values when the large board is left on?

[BZ58]

Also, if I were to upgrade some of the parts like the caps or choke, would the resistance values change?

[Paul Birkeland]

Are you reading a zero, or is the meter over limit? 

[BZ58]

It is reading 0, meter is not over a limit.

[BZ58]

Replaced the small board. Speedball has been reinstalled, both the small and large board. First thing I did was the resistance check. Measured the resistance at OB and OA on the large board. Readings for both are still 0. Checked the connections of those wires and all looks good to my eyes.

Taking a break from it now. I will redo the connections to OB and OA later and see if it works. Do you have any other suggestions?

[BZ58]

While reading through the forum I discovered that 0L on the meter may actually be OL, an abbreviation for “Over Limit”. Will need to be sure before plugging it in for the voltage check.

[Paul Birkeland]

Touch the probes together and look at your meter, that is a zero reading. 

Getting 0 Ohms at OA and OB on the big PC board means that your heatsink mounting kits aren't installed properly.  If your Crack was working previously, this is extremely unlikely.

[BZ58]

All went well. Thanks!

Then I decided to switch out the potentiometer. I bought it the same time as the Crack. Read that it was relatively easy. Not so easy in my experience today.

I removed the stock without clipping any wires. The one I was going to use doesn't have holes to pass the wire through, it has pins. Tried to solder onto those, and it wasn't going well, so I put the stock one back in. Twice an end of a wire broke from bending it too much. One of the wires was still long enough to use. The other one that broke from bending was the red wire that goes from the center lug of the the volume potentiometer to A7. I replaced this wire with some that I had left over.

Now when I turn it on, there is sound when I turn it up, but at very low volume, and it sounds distant and minimal detail. Kind of sounds like an old worn out cassette tape that you can hardly hear. Have I broken the potentiometer?

The tubes light up, the LEDs are lit.

I attached a couple pictures. Please pardon the sloppy appearance. Doing the best I can.

[BZ58]

picture 2

[BZ58]

Picture 3

[Paul Birkeland]

How are your voltages?

[BZ58]

Terminal  Voltage
OA    63.5 
OB   59
G    3.5
B+  190.6

[Paul Birkeland]

If you have 3.5V at G, then there's a bad solder joint between G and wherever you have your meter connected.

Your meter, however, might be showing you 3.5mV or 3.5uV, which wouldn't be a problem.

I sure would carefully inspect every solder joint in the amp where a black wire connects, I bet one is loose.

[BZ58]

Thanks, I’ll check my connections and work on it in a couple days, when I have a day off.

Really enjoy working on this amp, especially when it works!

Planning on rewiring some of the amp. Just ordered 22 gauge solid “hook up wire kit” that has 6 colors of wire in the package.

[BZ58]

I have a Film Capacitor 250V 2.2uF 10% PCM27.5

I am planning on connecting it to 20u and 21U. I'm doing this while leaving the stock 220μF 250V capacitor in place. This is referred to as the last power capacitor. The film capacitor is bipolar, so it doesn't matter which wire I connect to 20u and 21U.  Is this correct?

Reading the forums here, I am picking up bits of information to put together. I figure it's better safe than sorry to ask.