Crack & Speedball - Seeking advice re: no signal when powered on

[rburrows]

Hello Bottleheads,

I recently purchased a built-up Crack & Speedball unit from a user on head-fi.org. The Seller touched up the solder joints and verified functionality before sending off. The amp arrived very well-packed, but for whatever reason I am unable to hear sound when the unit is powered on. I am hoping a simple mechanical disturbance occurred in transit but I could use a little help in isolating the issue.

I confirmed proper functioning of source, interconnects, and headphones so I'm pretty sure it's a problem with the unit. Here are the things I have observed:

• After powering on, tube filaments light up in a seemingly normal fashion
• No LEDs in the circuit are lit when powered on, even after some time.
• During a couple power-up trials, I did notice a very faint, crackly signal in the left channel only if the volume control was maxed or near-maxed. It would fade to nothing in a matter of seconds. I cannot replicate this consistently.
• I went through the resistance checks from the manual and found that terminals 1,5,7,9,b3,b6 are all reading infinite resistance. Other terminals match the manual.

I am not very experienced with electronics, and nothing obviously visually wrong with the circuit stands out to me. The seller suggested the following:

"Reading through the manual, points 7 & 9 are what connect to b3 and b6, as well as connect to the larger speedball board. So that's something...

The part that gets me though is that power is out on both sides, which is odd because most of the circuit is two independant halves. Even the large speedball board is mostly mirrored across the middle. I find it very unlikely that there would be the same break/damage on both sides at the same spot. A shared path would be the (I think) ground. There's a wire from point 3U to G (page 25 of the speedball manual) that you could double check. I'm not entirely certain if that's a ground path, but it's the only thing I can think of at the moment."

That connection looks good but I am not sure how to confirm on the multi-meter.

Any advice would be greatly appreciated!

Thanks,
Robert B.

[Doc B.]

The very first thing to do is look over all of the solder connections with a magnifier and see if you can spot what came loose. Go ahead and do the voltage measurements too, and report the deviations from the manual. That will speed up the process of figuring out what is wrong. Since no LEDs are lighting it sounds like the problem is between the power transformer and the amp circuit - the rectifiers, the filter caps, and the associated resistors and connecting wires.

[rburrows]

Hmm, voltages are strange and weak:

1:  .8
2:   0
3:   0
4:   0
5:  .8
6:   0
7:  .1
8:   0
9:  .1
10:  0
11:  0
12:  0
13:  0
14:  0
15: .1
19:  0
20:  0

a1:  .8
a2:   0
a3:   0
a4:   0
a5:   0
a6: 1.3
a7:   0
a8:   0
a9:   0

b1: .8
b2: .2
b3: .4
b4: .8
b5: .2
b6: .8
b7:  0
b8:  0

[Doc B.]

If the heaters are glowing, you can measure nothing but essentially zero DC volts everywhere, and the meter is being used properly you have a problem at the power transformer high voltage secondaries. Switch your meter to AC volts, at least 400V scale, and measure the AC voltage across power transformer terminals 6 and 7 and then terminals 9 and 10. You should see around 150VAC.

[rburrows]

I am measuring 170 VAC between both 6&7 and 9&10. Using V~ 700 on my DMM.

For the VDC measurements I was using the V⎓ 200 setting on my DMM. at the next level up , V⎓ 1000,  those decimal values became zero.

[Doc B.]

OK, power transformer is good. Measure the DC voltage at terminal 21, red test lead to terminal 21 and black test lead to terminal 12. Use the 1000VDC range.

[rburrows]

Measuring 0 VDC between terminals 12 and 21.

[Doc B.]

OK, turn power off, unplug amp. If you have a diode check setting on your ohmmeter use that, if not, use around the 2K ohms or 20K ohms range. Measure across each UF4007 rectifier connected the strip on the right side of the power trans. They should read either around 500 to 1000 ohms or infinity depending upon which way the test leads are oriented. If you see a really low reading, like under 100 ohms, the rectifiers may be blown.

[rburrows]

I'm not sure if these readings make sense, I took them in both 20k and 200k ranges. I was getting all infinite on 2K range.

           20K    200K
          
18->20 : 19.66 : 106.4
18->21 : 18.15 :  92.2

19->20 : 19.55 : 106.5
19->21 :    OL : 109.5

[rburrows]

Silly me, I found the diode check setting on my DMM. Each rectifier is reading around .570 on the scale.

[Doc B.]

OK, assuming that your meter reads like most that means 570 ohms on the 2K ohm scale which is about right. If the rectifiers are intact and everything is connected properly you should have voltage at 21.

So these are the possibilities:

-The rectifier readings are actually .57 ohms and they are shorted out. It's not common that all would be dead, usually one or two blow if there is a short downstream from them in the circuit.

-Something in the power supply wiring may be shorted to ground. Look for a bare lead touching the chassis or a grounded terminal.
 
-Something is wrong with the connection at 21 or 12. It is possible that the black wire that goes from 12 to the headphone jack and then on around to the other ground connections is open somewhere.

-Just to cover all possibilities, it could be that your meter is messed up on the DC volts reading. This however does not explain why the LEDs aren't lighting up, so that is a pretty slim possibility.

-I think you are on the right track thinking that something got moved the wrong way in transit. At this point my best guess is that close examination of all of the connections at every terminal to make sure everything is still connected could find the problem. I would also ask the seller to pick his brains about what might be wrong, as he may recall a problem area.

Hang in there, lately we've been getting the majority of folks with problems up and running in a day or two.

[InfernoSTi]

Can I just say that Bottlehead (Doc, Paul, et al) are the greatest customer service folks in the business?  My hat is off to you guys....

John

[rburrows]

A-ha. So I found that the wire between 18L and 10 was loose at the 10 terminal. I re-seated the wire and added a fresh bit of a solder and now the Crack is making sweet music!

Wow John, no kidding.

Thank you Doc for getting me on the right track so quickly and so clearly. Troubleshooting with you was a breeze

[Laudanum]

A-ha. So I found that the wire between 18L and 10 was loose at the 10 terminal. I re-seated the wire and added a fresh bit of a solder and now the Crack is making sweet music!

Wow John, no kidding.

Thank you Doc for getting me on the right track so quickly and so clearly. Troubleshooting with you was a breeze

[rburrows]

Spent the afternoon demoing some albums on the Crack, and it's sounding really nice. But I have a bonus question

I'm noticing a slight hiss in the left channel only. It remains at a constant low volume independent of volume knob level. Doesn't seem to matter if interconnects are in or not. The right channel is noise free. (just FYI there is a separate, lower pitched hum that is dependent on the volume knob, but is only slightly noticeable when maxed. This is even across the two channels. It's not an issue at all at normal levels but I'm just pointing it out for contrast)

Checked on a couple sets of headphones and the left channel hiss is there for each. Could this be another case of disturbed soldering joints, introducing noise? If that seems plausible I'll go through the connections again.

Thanks!