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Barton Arpeggiator rev 2.0 Issue
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author Barton Arpeggiator rev 2.0 Issue
Hello all,
I Have been in contact w/ Mr. Barton and he has helped me immensly so far on this issue, but I thought I'd reach out to the community here instead of pestering him too much. I'm fairly new to DIY synth/Electronics, and self taught. I recently got the BMC arpeggiator rev 2.0 without the expander board. I followed the PDF file from his site for this version but I have not been able to figure it out. Usually I can troubleshoot and get it working but this one has me stumped.
It started out as looking like a simple short, the 10r resistor for +12v would smoke. I made sure and confirmed that my power supply was not reversed and tried again, but same thing. Tested w/ a DMM and I am getting a short across +5v and GND. However there's a few other things that come up as well:

-If the 'Move' pot is turned all the way CCW, it shorts, causing 10r resistor to smoke
-switching diodes from 4148 to 1n914, no change
-on a scope, I can see the pulse output from the PIC, but i no longer see it on the other side of the 100r resistors (leading to the trigger output)
-no change when 'CKEN' shorted to GND
-All of my outputs (trig, gate, cv out) show a constant 5v
-checked components a zillion times and all values are correct, trimpot, pots
-Scope shows me pwm and pulse outputs coming out of the tl074 but nowhere else

Mr. Barton was gracious enough to send me a replacement pcb in case it was a faulty trace, but the 2nd one is doing the same thing, and I feel foolish contacting him again saying it still won't work...Anyone has any tips it would be greatly appreciated. I know it either has to be a faulty/incorrect part or a dumb mistake on my part. if a pic is needed I can post it as well. THANKS!
Have you tried replacing the 5Volt regulator?
5v regulator (7805) was replaced w new one, but w no difference in behavior. same as on the 2nd board... confused
post a highrez pic of both sides.
it sounds like a short somewhere. or maybe a reversed part.
here's a pic of the front and back of the board. This is the second one, as I just finished completely desoldering the first.
I did also search through the forum here, I did see one post about a different BMC module w/similar problem, but their solution was that the silkscreen for the power supply was for MOTM and was listed in the build guide as such. Dont think its the case for this one as I'm at least getting 5v (5.16v) on my DMM. Also noticed the TL074 gets pretty warm when i test it out. And I've switched out multiple 074's to make sure it wasn't just a bad one. Could it poss be that it would only work w/the expander board?
Do you happen to have a full schematic? The way it's broken up into chunks in the PDF document is a bit difficult. From what I can see though, the expansion board just takes CVs from the main board and mixes them with an attenuated additional CV, so I don't see why that would be any issue that you don't have the expansion board.

The 074 getting quite warm is concerning though. I would look for your problem around that circuit.!
@devinw1 Much appreciated, i will be checking again around the 074. I know to check for a short between +5v and gnd but not sure what else to check for short wise. Also, i would def check a schematic if it was available, however seeing as it's Barton proprietary i figure i wouldnt be privy to the whole thing. I was given a layout of all the power traces, but still havent found the short or issue. Unless Mr. Barton were to chime in with a schemo, i just figured more heads together from Muff community might help too.
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