SOLVED Low tide destroyed pad

[Mentaltossflycoon]

So I've be hoping to keep this thing out of this forum but here is my shame. This was getting close, everything seemed to be working except for the mix knob. Full wet and full dry sounded fine but anything between was a huge volume drop. I assumed that pot to be bad and when I first put this together, I had the right value wrong taper double gang on hand for the slew control thinking "whatever, you know how to remove a pot." Well, I botched this one tonight while replacing both pots taking the pad along with the last lug. 8 out of 9 joints went fine. Any suggestions where I should go from here? Much thanks!

 

[Jonnytexas]

I would follow the trace above the bad pad and just hardwire from that lug of the pot to wherever that trace goes.. No big deal, it will work.

 

[Mentaltossflycoon]

Thanks!

 

[Harry Klippton]

I would follow the trace above the bad pad and just hardwire from that lug of the pot to wherever that trace goes.. No big deal, it will work.

This is usually less brutal than scraping back the top layer to reveal the trace and soldering straight to that I think

 

[Mentaltossflycoon]

Ok so I fixed the slew issue, but replacing the mix pot wasn't the problem there. So it seems I have slightly low output with the level at max and the mix at both extremes and then very low out put anywhere in between. Could this be related to the j201 I have where there should be a 2sk208-y? I'll take some photos and some readings and post later tonight, turn this into a full on troubleshoot.

 

[Mentaltossflycoon]

So here's a few pics. I didn't want to bend the pots back but I can if necessary. If you fear the black tape, look away now. I took these voltages but I don't really know what I'm looking at. The right hand 2n3904 had lower voltages than the others, is that something? Also, if there's a more preferred way to lay this type of info out, I can rearrange these numbers. On the transistors and fets, I just wrote down the values left to right

Ic1
8.8
0
5

Ic2
4.7 | 5
5 | 4.8
4.8 | 5
0. | 1.6-2.8

Ic3
1.4 | 0
4.9 | 4.9
4.7 | 4.7
4.7 | 4.7
5.8 | 5.9
0 | 8.8
5.8 | 5.9
4.7 | 4.7

Ic4
1.6 | 8.8
2.5 | 2.1
2.5 | 2.1
0 | 2.1

Ic5
2 | 5
2 | 2
2 | 2
0 | 2

Ic6
6.4 | 5
2.4 | 2.2
2.4 | 5
2.4 | 6mV
0 | 3.4
0.6 | 0.6
0.6 | 3.1
0 | 1.9

Ic7
2 | 2.7
2 | 2.7
2 | 2.4
0 | 5

J201
6.7
6
6

2sk208y(j201 subbed)
6.75
7.3
8.8

2n4904s
Left. 6.7 | 7.3 | 8.8
Middle 6.1 | 6.7 | 8.8
Right. 3.5 | 3.6 | 5.3

 

[Jonnytexas]

You need to clean that board with some isopropyl to get that flux off. Some of the solder joints look a litle dodgy, especially to the 10:00 of the B100k pot. That ends my troubleshooting skills.

 

[bowanderror]

You need to clean that board with some isopropyl to get that flux off. Some of the solder joints look a litle dodgy, especially to the 10:00 of the B100k pot. That ends my troubleshooting skills.

Agreed, those joints I believe are for the LM13700, which the voltages looks fine for except for pin 16. Pin 1 & Pin 16 are the OTA control inputs, and should be the same voltage.

Both of your JFET ( Q1 & Q4) voltages also look off. My Q1 voltages were around :

• Drain - 4.5V
• Source - 1V
• Gate - 0V

I used a 2SK30A-Y, but yours should still be similar. I don't have my Q4 voltages offhand, but they should be similar as well.

Are you sure they are real JFETs? Even SMD can be fake these days, unfortunately. If you have a transistor tester or the Greatly Improved Transistor Matcher vero layout, you can test them there. I would also try swapping the pins around, as you can't really destroy a JFET in this circuit.

 

[Mentaltossflycoon]

Don't have a tester but I can try some fresh j201 from this batch. Could have toasted them somehow. They're from mouser if that makes any difference.

I went through and rewet everything and scrubbed w iso with no changes thus far.

 

[Mentaltossflycoon]

You're talking about a specialized transistor tester, not the little thing on my multimeter, right? I do have that.

 

[Mentaltossflycoon]

New j201s did it! Ahhhhhhhh mixxxx kknobbbbb. This circuit is very very cool. Can't wait to box it up. I have a ball silver just waiting for some scratches. Thanks for the help, pals.

 

[fig]

You have a tester now....incoming message