SHEcho not working

[ranchak]

I also have a SHEcho that doesn't work. I did repair the trace that is missing above C26. I do not have any repeats with mine, just the straight signal mixed with a bit of distortion. Anybody have any ideas?

[Dean Hazelwanter]

Hi,

Check the voltages, especially the +5v in the digital section. Can you take some pictures of your board?

[ranchak]

Hi Dean, here are my voltages:

Vref= 12.40


Q1

C  12.50
B   6.00
E   5.46

U5

C  12.50
B   0.00
E  .267

U1

1    12.40
2     6.19
3     6.19
4     5.65
5     0.00
6     6.19
7     6.19
8     6.20


U2


1    .630
2   1.782
3   1.782
4  12.34
5    1.786
6    1.783
7    1.790
8    1.783
9    1.783
10  6.68
11  6.68
12   1.786
13   0.00
14    1.782
15    1.782
16     .360


U3


1     0.00
2      .117
3      .229
4      .170
5      .171
6      .173
7      .172
8      .174
9      .267
10    .063
11    .051
12    .056
13    .048
14     .046
15     .080
16     .052


U4


1     .267
2     .110
3     .160
4     .211
5     .159
6     .111
7     .160
8     .160
9     .147
10   .158
11   .159
12   .159
13   .185
14   .164
15   0.00
16  .107
17   .108
18   .121
19    .121
20    0.00
21    .532
22    .068
23    .065
24   .021

[Dean Hazelwanter]

U5 is a 78L05 voltage regulator. It's pinout (looking at the flat face, pins down) is OUT, COMMON, IN. There is no +5v at the output of the regulator, or at either chip in the digital area (U3, U4). So, either the regulator is bad, in wrong, or something in that area is dragging down the +5v supply. If U3 and U4 are socketed you can remove them and see if your +5 comes back, but my money is on U5 being in wrong, dead, or not really a 78L05.

Can you take a component side picture of this area?

[ranchak]

The 78L05 is bad. I bench tested another one and it works fine. I installed it in the circuit and my voltages are a bit higher ( .267 up to .897), but still not 5 volts on the output of the regulator. I'm going to do some troubleshooting in this area and I will get back to you. Thanks, Ron

[ranchak]

OK, I had two bad regulators. I found a good one, I have 4.6v at pin 9 on U3 and 4.6v at pin 1 on U4. I still do not have any echo. I did put a jumper instead of R27, but I did replace it with a 10ohm resistor.






I'm going to check all of my component values next.

[Dean Hazelwanter]

I have 4.6v at pin 9 on U3 and 4.6v at pin 1 on U4.

Those aren't power supply pins - what voltage do you see at U3 pin 8 and U4 pin 24?

Do you have an audio probe? If so, poke around to see where you lose the delayed sound. You do have clean (un-delayed) signal at the output, right?

As usual, get back to me (us) so we can get this thing running for you.

[ranchak]

Dean, I have .362v at pin 24 U4 and .822v at pin 8 U3. I loose my audio at the junction of R2 and R8. I unsoldered R2 and R8, both tested fine. The audio is barely audible through R2, but it is there. Once R2 and R8 are installed back in the circuit the audio is lost at this junction. Oh yeah, I do have clean signal at the output.

[Dean Hazelwanter]

I have .362v at pin 24 U4 and .822v at pin 8 U3

So you still don't have the +5v supply that U3 and U4 need to operate. That's the big problem at this point. Remove U3 and U4 and see if you then have +5v on pin 24 U4 and pin 8 U3. If yes, U3 or U4 (or both) is bad. If not, leave them out and figure out why you don't have +5v. First suspect is the 78L05. If it's bad, it's likely something is killing them, since you had 2 others go south. Check that circuitry *very* closely for shorted tracks/pads. Less likely is that either C21 or C22 is shorted. Did you put in the correct value (4.7 ohms) for R27?

I loose my audio at the junction of R2 and R8.

I wouldn't expect to see a signal at that point - it's Vref. But again, you don't care about this (or anything else) until you get the +5v situation fixed.

[ranchak]

Hi Dean, I have a dyslexia problem. I DO have 4.99v at pin 24 and 8. I was looking at them backwards! The 78L05 are from a previous project and I think I may have fried them in that project. I do not have a 4.7 ohm resistor, I used a 10 ohm (the smallest that I could find). Sorry about that. Now where do we go?

[Dean Hazelwanter]

I DO have 4.99v at pin 24 and 8

With U3 and U4 installed, right? If so, that's good - and it means the 78L05 isn't dead.

I do not have a 4.7 ohm resistor, I used a 10 ohm

Use two 10 ohm resistors in parallel to give you 5 ohms.

Now where do we go?

Back to the audio probe. See where you lose the signal, checking at key places. You have a clean signal, so you should see it at U1 pin 7. Check at U2 pin 10. Still got it? Try U4 pin 2 and 3. Still got it? Try U4 pin 4. Still got it? Try U2 Pin 2&3. Still got it? Try U2 pin 6&7. Once you know where you lose the signal, you have a sub section to look at more closely.

[ranchak]

I have audio at pin 7 on U1. There is no audio on pin 10 on U2. There is audio on pin 11 of U2. No audio past U2.

[Dean Hazelwanter]

In your initial voltage readings, you had U2 pin 13 as 0 v. If that is still the case, that's the problem. If you transposed pins 13 for 4, and you really do have +9 (or +12.34) on pin 13, the voltage to U2 is ok and it's one (or more) of...

- U2 is bad (not possible with 'The Edge')  ,
- One of the components around U2 is bad, or wrong value,
- There is a bad solder joint, broken or shorted tracks in this area.

I would start by cleaning the board, especially in this area. Then you can check for shorts, broken traces etc - use a magnifier of some sort.

[ranchak]

Hi Dean, I haven't had any free time to troubleshoot. I am going to try to look at it tomorrow. I will get back to you and let you know what I find.  Thanks, Ron

[Dean Hazelwanter]

Hi Ron,

I won't have computer access after tonight for a couple of days, so don't take it personally if I don't reply right away.

[ranchak]

Hi Dean, thanks for the update. I haven't had time to look at this project. I'm busy finishing my biasing tool and a power supply. I'll probably be back at it on Wednesday or Thursday. Thanks, Ron