Tri-Vibe trauma

[T_MBaker]

G'day,

So, I'm having trouble with my tri-vibe build. I've used the PCB sold by Chi_boy, build doc
http://home.comcast.net/~gprause/BuildDocs/TriVibe_V3.1_Build_Doc.pdf

LM13600 datasheet http://pdf1.alldatasheet.com/datasheet-pdf/view/8638/NSC/LM13600.html

Firstly, I have reflowed all solder joints, so there shouldn't be any cold solder joints. I have checked all resistor and capacitor values visually.

In the vibe position there is basically no sound (though if the amp is turned all the way up low volume sound can be heard)
In the other 2 switch positions the signal passes through un-modulated at about unity volume. This tells me that the signal is bybassing the 13600 and instead going through R18 or R19

I've narrowed the probable problem area down to pins 9, 10, and 12 of the LM13600.
Their respective voltages are 1.5V, ~0.2V, and ~0.2V. Based on the voltage lists I have found elsewhere, pin 9 should be 4-4.5V, and pins 10 and 12 should be approx 5.5V. The voltages at all other IC pins measure correctly.

Following the path with a signal probe, the first half of the IC works as expected, that is, signal enters at pin 7 exits at pin 8 with modulation. Depth and rate knobs affect modulation. All working as it should.
Next, following the path from pin 8 through C4(1n5) to pin 10 the signal is as it should be. It is at pin 9 where the signal basically stops. Now, if I absolutely crank the volume on the amp, I can hear the sound of the modulated guitar signal (definately the guitar signal, not some LFO noise).   

So, I'm hoping for some fresh thinking and possibly somebody with a better understanding of the LM13600 or the circuit. I can post pictures if needed, I'm just waiting on the battery in my iphone to charge.

Thanks,
Todd

[cooder]

Hi Todd,
I've also built the TriVibe on ChiBoy board and had a bit of a mission getting it going, by the description it sounds similar to what I had.
I didn't have sound in the middle position of switch and only very faint modualtion (if at all) on the outer position of switch, one switch position was less volume (below unity).
Anyway, I didn't take voltages (but can do so if it helps you), did also reflowing of solder joints and the other thing I noticed was the polarity pads for the LEDs are marked opposite to most other fabbed boards I had so far. The cathode/negative side of LED should be on the square pad of board, maybe you wanna check that out.
I did those things, checked resistor, caps etc, but still no cigar.

What however (to my surprise) fixed my build was swapping in another LM16000 that I had lying around, and bingo it was all good.
The one I replaced it with was from Tayda I believe.
So if you have another spare chip maybe try swapping them. I usually suspect dodgy components last as it's more often a dry solder joint or a mix up of sorts when populating in my experience, but this time it was indeed the IC  for me.

Hope this might help a bit and if you'd like me to take voltages on mine (still haven't boxed it up, but it works fine on testrig), let me know.

[T_MBaker]

Thanks for the reply Cooder.

I don't have the tri-vibe with me at the moment, but I'll double check the LEDs when I get home.
I would have to say that I have been looking at the LM13600 with suspicion. It seemed odd that it wasn't working how it should considering everything else is correct. I'll have to dig around and look for a replacement. Hopefully that'll be the solution!

Thanks again.

[T_MBaker]

Just thought I'd give an update (mostly for those who stumble upon this thread with a similar problem).

I tried one other LM13600 I had with exactly the same result (i.e. not working). Both were purchased from Tayda.

Ordered a few NJM13600s from Small Bear. They just arrived. Stuck one in the socket. Worked!!

So, it is possible that Tayda has a batch of bad LM13600s. I don't have any other circuits I can test them in to be 100% sure though.

[cooder]

Great to hear it's now going for you as well! As said, I had a bad LM 16000 as well and swapping it did the trick luckily. I'm not a hundred percent sure, but I think both my chips were from Tayda, but I believe ordered at different times, so may have been different batches.