Crack resistance check problem [resolved]

[pyflaw]

Hello,

I bought the Crack kit back in 2016. My son completed the soldering a few years back but he thought he melted the power switch a bit while soldering and did not proceed to perform the resistance and voltage checks.

Today, I visually checked the power switch and it looked fine to me. So, I proceeded with the resistance checking. All terminals resistance seems fine except terminal 13 which measured at 0.528k ohms instead of " * will slowly climb to 270k ohms" as per the manual.

Is 0.528k ohms acceptable to proceed to the voltage checks? By the way, I have the same 0.528k ohms reading at terminal 2 and 4.

If not, any advise on what I should check for next?

Thanks!
 

[Paul Birkeland]

Is it 528K?  That would be 528,000 ohms and would be OK.  0.528K would be 528 ohms, and that will blow the fuse as soon as you turn it on.

[pyflaw]

It is 0.528k (528) ohms.

[Paul Birkeland]

Definitely do not attempt to power up this amp.  Can you post some build photos?

[pyflaw]

Let me know if you want to zoom in to certain part or take them from different angles.

Thanks!

[Doc B.]

It's a bit difficult to see the connections of the 270 ohm 5W resistor that should be connected between terminals 13 and 15. I would double check those connections. If it is connected to the wrong terminals it could give the low reading you are seeing - for example maybe miswired to terminal 14 or 16 rather than terminal 15, or to terminal 12 rather than 13.

[pyflaw]

The leads of the 270 ohm 5W resistor (white rectangular resistor) are connected to 15L and 13L.

Thanks! 

[Paul Birkeland]

The diodes going to 21 and 22 look like they have their leads touching. The diode between 18 and 21 is out of position.  Even if this ends up not being your issue, those leads touching will cause major issues.  If they are touching, you'd expect terminal 13, B2, and B5 to be about 540 ohms...

[pyflaw]

The diodes that go from 19 to 20 and 19 to 21 (first photo) seem fine (not touching) but the diodes that go from 18 to 20 and 18 to 21 seem touching each other on the terminal 20 and 21 side (second photo). I have adjusted the leads to keep them away (third photo).

I remeasured the resistance at terminal 13. It is much higher now but it kept changing and did not seem to settle at a final value. It started with a high value like 8, 9 M ohm and went down slowly to may be around 1 M ohm and then jump to 10 to 20 k ohm and then went up in value to around 200 k ohm and then jump back to a couple of M ohm and then went down in value and kept on jumping back and forth. The terminals at B2 and B5 behaved the same way as terminal 13.

Does this pass the resistance check that I can proceed to the voltage check?

Thanks!

[Paul Birkeland]

I did not notice initially that this is the older 1.0 version of the kit, so the wiring instructions for the diodes aren't as specific.  Based on what you see now, you can perform the voltage checks.

[pyflaw]

1. I proceeded with the voltage checks. Most of the terminals are within 10 to 15% of the expected voltages except three terminals 5, A1 and B4. The actual readings for all three terminals are around 56.7 V.

2. Next, I connected a source to the inputs and plugged in my headphones. There was a loud hum on the left channel even the volume was set to the lowest.

Any advice on what I should check for?

Thanks!

[Paul Birkeland]

When you do a voltage check on a piece of equipment like this and the voltages aren't correct, then the amp isn't working.  When you connect your headphones to an amp in these conditions and try to use it, you are plugging your headphones into an amp that isn't working.  This can destroy your headphones depending on the issue(s) you're having and there's no extra information to be gained by doing this.

Now, off the soap box, are the two lugs on the volume pot with black wires on them connected with a jumper?

[pyflaw]

Thanks for your advice on not to connect my headphones to an amp that isn't working.

The two lugs on the volume pot with black wires are connected with a jumper wire.

Thanks!

[Paul Birkeland]

Could you post a closer shot of the 9 pin wiring?

[pyflaw]

Let me know if these are not sufficient or you would like to zoom in to certain pins or take it from different angles.

Thanks!