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My TT-303 (MK1) just died :(
MUFF WIGGLER Forum Index -> Music Tech DIY  
Author My TT-303 (MK1) just died :(
LektroiD
I was using it fine, then I plugged in my RAT distortion using a power splitter cable (the sort you use for sharing 1 PSU between several stompboxes). It flashed few lights, then went off.

It would not power back up (the internal LED is lit when I switch on). I checked the PSU I was using and it is only rated at 300ma, so sharing it may have starved it of current, but I can't see how this would kill my TT.

I found a 1A PSU, and when I power it back up the Function and Accent LEDs are lit for a while then it powers itself down sporadically. Nothing seems to do anything, although I can switch between the Accent and Slide, but that's all - basically the lights are on but nobody's home.

I wonder if a VREG has blown, I'm not sure of the expected voltage or pinouts of the VREG (there are two inside). That said, I am getting voltage at the test points, but the 6V looks low:
TP (5.33) = 5.33V
TP (6V) = 4.32V

Any help would be most welcome
guest
does midi out work? midi in? are there any CV outs/ins that you can test? this will help determine if the problem is on the digital or analog side.

there should be a 12V rail somewhere, check the power pins of one of the opamps. there should also be a digital logic rail, probably 3.3V, but maybe 5V. check the power pins on some of one of the digital logic ICs. if there is a switching powersupply in there, it most likely went. starving a switching supply forces it to try to ramp up the output current, which blows the output transistors.
EATyourGUITAR
I'm pretty sure you just connected the + and - on your power supply. this happens when one guitar pedal is shorting the ring of the audio cable to the negative supply while the other guitar pedal is shorting the ring to the positive supply. it doesn't make magic smoke till you patch them together with a TS cable. I assume you were putting the audio output of the 303 into the audio input of the RAT distortion? one of two things will happen. the smallest copper conductor in the shortest path will become a fuse. or the power supply will die or spike, sag, overheat, go into temporary protection mode etc..

people say 9v negative ground or 9v positive ground but this is actually not a proper description since ground is always 0v in every case to be exact. 9v center negative or center positive only describes the power entry port. it does not describe how the audio ground is or is not tied to one of the power rails. it is best not to share a power supply unless they are all of exactly the same type and the polarity of the barrel connector is checked before hand.
LektroiD
So, the voltages at the test points are as follows:
TP 5.33V = 5.333V (it was initially over by a few mV, so I recalibrated this using the 5.33V trimpot)
TP 6V = 4.583V
TP 12V = 11.946V

Looks like they are all in spec except the 6V rail, which is testing at 4.583V

There are codes on the three SMD VREG's:
Q37: DMw 5G2 G01
Q38: HY 37
Q39: DE 5B4

I will get some batteries later today to see if that brings it alive.
guest
there is a seperate digital rail, be sure to check that. the 6V only powers the headphone amp, so its not likely the culprit (although needs to be fixed). check the signal from the mix-out, is that working ok?
EATyourGUITAR
I believe it is not the + rail that is the problem. I think some part of the PCB has a burned ground trace. the entire circuit makes a network that will put stray voltage into areas that would normally be powered differently. or going the other way around, something got hot and failed closed.

you need to probe both the input and the output of all the regulators. check the regulators are LDO type. if they are LDO they need maybe .5v or 1v minimum drop from input to output. non LDO needs maybe 2.5 to 3v from input to output. dropout for most regulators is around 2.5v. if the input of a regulator is output+1v then the output will be = input-2.4v = 4.583v

you should also check if any regulators are getting hot. this is a good way to find the problem. when I had a blown mosfet one time it was pulling 100ma shorting to ground. the regulator was also sagging because the load was bigger than the rated output. exactly like what you showed here.
LektroiD
guest wrote:
check the signal from the mix-out, is that working ok?


It would be helpful if I could get it to start, but it won't run. Although, I can get it to play random notes when I click between the Accent and Slide buttons though, so the synth side is healthy.

I tried MIDI'ing it up to the Cyclone Studio app, and it just caused the app to freeze.
mush
I burnt a shift-registered on one of mine when plugging in another one via split power cable - while having power on. It was an easy fix for me as I just had some of the buttons dying on me, and could trace them in the button/led matrix to that shift-reg.

That accent and slide buttons "work" makes it sound as the CPU is intact, but you got dead shift registers too.
LektroiD
mush wrote:
I burnt a shift-registered on one of mine when plugging in another one via split power cable - while having power on. It was an easy fix for me as I just had some of the buttons dying on me, and could trace them in the button/led matrix to that shift-reg.

That accent and slide buttons "work" makes it sound as the CPU is intact, but you got dead shift registers too.


Interesting! Can you remember the location and part number of the shift register you had the problem with?
mush
It was on the button/led board. IIRC it was just one kind of IC on that board. I can't remember the exact part, but it was a fairly common SOIC.
Edit: it may have been a multiplexer/demultiplexer ic. But still just a standard ic.

It can be seen on the third picture here:
https://www.instagram.com/p/BY99tktHqik/?igshid=4l48d0hrvcgy
LektroiD
mush wrote:
It was on the button/led board. IIRC it was just one kind of IC on that board. I can't remember the exact part, but it was a fairly common SOIC.
Edit: it may have been a multiplexer/demultiplexer ic. But still just a standard ic.

It can be seen on the third picture here:
https://www.instagram.com/p/BY99tktHqik/?igshid=4l48d0hrvcgy


Many thanks for this. The part in question is a 74HC138AG dmux. I couldn't find the actual part unless I ordered from China, although I managed to find a 74HC138D (which I'm hoping works the same). If that doesn't fix it, I spotted a dmux or two on the main PCB which I could change.

Out of interest, how did you locate the fault? I would never have found that in a million years.
mush
I found out that the tt303 worked, but that the buttons had the wrong functions. I checked what buttons didn't work and traced their signals on the pcb. I assumed it would be a mux/demux/shiftreg or diodes that were faulty as most button-interfaces (or keyboards) are based on a diode-matrix. The diodes did conduct signal, so it was down to the IC that they connected into. (It was a year or two ago, but that is how I remember the trouble shooting process)
LektroiD
None of the buttons on mine are doing what they should. It's basically gone haywire. Let's see if replacing the mux/dmux helps... If not, a friend is sending me the remains of a mostly stripped v1.0 board, which still has all the chips and power circuitry intact.
mush
LektroiD wrote:
None of the buttons on mine are doing what they should. It's basically gone haywire. Let's see if replacing the mux/dmux helps... If not, a friend is sending me the remains of a mostly stripped v1.0 board, which still has all the chips and power circuitry intact.


Sounds like the same problem but you may have toasted more than one IC. It would surprise me if there's anything else giving that kind of problems.
LektroiD
Replaced the mux/dmux chip and et voila, it's alive again! All my patterns are still in place too!
hyper hyper hyper hyper hyper

Huge thanks, mush for pin-pointing the problem! we're not worthy
spotta
LektroiD wrote:
Replaced the mux/dmux chip and et voila, it's alive again! All my patterns are still in place too!
hyper hyper hyper hyper hyper

Huge thanks, mush for pin-pointing the problem! we're not worthy

SlayerBadger!
mush
Wonderful to hear! Guinness ftw!
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