MST Dual AD/ ASR Envelope Issues

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Maxx mayhem
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Post by Maxx mayhem » Tue May 24, 2016 5:56 pm

silenttxa wrote:I too have had issues. I've assembled most other MST/Synthrotek modules with no problems until i started working on this guy. I first bought the kit, which was missing some pots and switches from Sythrotek, and they sent out the missing parts.

Never got it to work, so i bought the PCB and put a BOM together of the parts needed for the rear PCB. 2nd try i can get it to work, only if i wiggle the power plug into place. Even then the lights on the front are extremely dim.I noticed that the guide on the site has not been updated to accommodate the latest PCB rev, as some components have been moved, etc.
Sounds like a possible weak solder joint on the power bus connector. I'd suggest reheating those pins and see if you have any better luck.

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Post by calaveras » Wed Aug 31, 2016 10:26 am

well after a busy last 4 or 5 months I'm going to be revisiting this and my bricked MST VCO.
I think I am going to start by checking the diodes and lytic caps.
I've noticed that the lytics in the pic on the build page are quite a bit large than the ones that I used. (I did PCB/panel)
I am wondering if I underspecced these.

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Post by mmm » Wed Aug 31, 2016 11:48 am

calaveras wrote:well after a busy last 4 or 5 months I'm going to be revisiting this and my bricked MST VCO.
I think I am going to start by checking the diodes and lytic caps.
I've noticed that the lytics in the pic on the build page are quite a bit large than the ones that I used. (I did PCB/panel)
I am wondering if I underspecced these.
Here's my notes on the VCO:
The electrolytic caps are just for power input filtering. You can actually not use them if your power is stable. Just make sure they have at least 16WVDC if you do use them.

A couple of things I've run into:
Make sure your FETS have the same pin out as The ones spec'd. Alternate pinouts sorta don't work. Same with the transistors.
Yes, I've been stupid enough to do this....

Make sure all other caps are the correct value and in the right spot.

Make sure you didn't overheat the Polystyrene cap. It's aluminum foil wrapped around styrofoam. The styrofoam melts if the leads are overheated and totally messes up the cap. this is THE VCO core cap. So, it's really important.

Make sure the jumper is off the 2 pin header when you try it the first time. That shorts out the CV inputs from the exponential network at the front end of the VCO core so that the linearity can be set.
Try cranking the LIN trim clockwise to see if it will oscillate at some point.

As usual, look for cold or missed solder joints, make sure all of the resistors are correct, the ICs are in the right direction...typical stuff.

Edit: Oh, yeah, ran into this last week. Make sure the trim pots are in the right spots and the correct value. A friend of mine just put them in thinking they were the same without checking values.
That was fun to troubleshoot....
G

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Post by calaveras » Wed Aug 31, 2016 10:53 pm

Thanks for the pointers.
I went over both the AD/ASR and the VCO and verified all the diodes are good.
I'm going to see if I have another poly cap.

As far as the chips go, I got all TI versions of the CD4011be, TL071cp, LT1013dip and TL074CN.
I didn't deviate from the BOM with those did I?

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Post by mmm » Thu Sep 01, 2016 11:02 am

calaveras wrote:
As far as the chips go, I got all TI versions of the CD4011be, TL071cp, LT1013dip and TL074CN.
I didn't deviate from the BOM with those did I?
Nope. They should be OK.

G

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Post by calaveras » Fri Sep 02, 2016 12:03 pm

couple pix of my stillborn baby.
Image

I'm going to try what another poster mentioned about pulling the chips and checking that the voltages at the various pin positions make some kind of sense. I am guessing that in a few places I am not going to be able to expect more than power and ground, since without the chips, there might not be anything driving a voltage.
Last edited by calaveras on Fri Sep 02, 2016 11:43 pm, edited 1 time in total.

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Post by mmm » Fri Sep 02, 2016 12:47 pm

calaveras wrote:couple pix of my stillborn baby.
Image

Image
I'm going to try what another poster mentioned about pulling the chips and checking that the voltages at the various pin positions make some kind of sense. I am guessing that in a few places I am not going to be able to expect more than power and ground, since without the chips, there might not be anything driving a voltage.
If you get your PSU supply voltage less around a volt at the chip power input pins, at least you know the power input diodes are OK.

the pix are really dark. i can't read the resistor values.

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Post by calaveras » Fri Sep 02, 2016 11:48 pm

updated with a better photo. Haven't had time to test today, my demonic nephew was in town.

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Post by calaveras » Sun Sep 18, 2016 12:37 am

Okay I passed my Certification exam.
I can spare some time to mess with this again.
Pulled all the chips.
Plugged in to my tester supply,
looked up the pinouts of the chippies.
The pins of the TL074 and the 4011 are showing the right supply voltages at least. Also ground seems to be working everywhere it should.
I'm not clear on what the other pins should be reading?

As far as my bricky VCO, I'm waiting for a batch of parts to show up. Gonna replace the polystyrene cap. I think I overheated it.
Curious, the Synthrotek site links to a mouser part which is a plain jane poly film, not polystyrene. Is that an acceptable alternate?

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Post by mmm » Sun Sep 18, 2016 11:54 am

calaveras wrote:Okay I passed my Certification exam.
I can spare some time to mess with this again.
Pulled all the chips.
Plugged in to my tester supply,
looked up the pinouts of the chippies.
The pins of the TL074 and the 4011 are showing the right supply voltages at least. Also ground seems to be working everywhere it should.
I'm not clear on what the other pins should be reading?

As far as my bricky VCO, I'm waiting for a batch of parts to show up. Gonna replace the polystyrene cap. I think I overheated it.
Curious, the Synthrotek site links to a mouser part which is a plain jane poly film, not polystyrene. Is that an acceptable alternate?
The Poly film on the VCO should work. I never tried one. I always use the 23PW250 PS cap shown in their visual BOM. never tried the poly film.

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Post by calaveras » Fri Oct 07, 2016 10:00 pm

I stuck the ply film in there, no dice. I'm going through now and checking all the resistors to be sure I didnt bork any of those. Though of course in a few places with megaohm resistors it seem my probes are finding a cheaper path around that resistor.
I'm also going to re-wet a bunch of the joints.

On to the AD/ASR, I'm going to try the same there. Re-flow joints and re-confirm all the resistor values.
le sigh...

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Post by mmm » Sat Oct 08, 2016 12:39 pm

calaveras wrote:I stuck the ply film in there, no dice. I'm going through now and checking all the resistors to be sure I didnt bork any of those. Though of course in a few places with megaohm resistors it seem my probes are finding a cheaper path around that resistor.
I'm also going to re-wet a bunch of the joints.

On to the AD/ASR, I'm going to try the same there. Re-flow joints and re-confirm all the resistor values.
le sigh...
Make sure the jumper isn't connected when you try it. That shorts out the entire CV input to the VCO core and is used for calibrating the core only.
Also, make sure all your trims are centered.

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Post by calaveras » Sat Oct 08, 2016 2:45 pm

Thanks for the input.
Yeah the jumper is not on.
The AD/ASR is behaving such that it outputs a low couple millivolts, which thumps (on the scope) when I actuate any of the switches.
The VCO is not outputting anything when I manipulate the switches.
I'm gonna try and get to this monday. I am at machines in music today and the neph is coming over tomorrow so nothing productive happens. yay.

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Post by stringsthings » Sun Dec 11, 2016 11:43 am

Did you get the VCO and/or AD/ASR working? I had probs with my VCO and it turned out that there was some solder joints on the back that were shorting out to other joints. Using a magnifyer, I was able to find the shorts. I think I actually had three. ( I've since switched to a finer tip for my soldering iron; works much better )

If you need any voltages for the IC's, I can probably help.

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Post by calaveras » Sun Dec 11, 2016 11:54 am

yeah they are still sitting in my 'to fix' pile.
Kinda soured my previously rosy opinion of Synthrotek.
If you could give me a hint as to which parts you found shorted?

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Post by stringsthings » Sun Dec 11, 2016 3:51 pm

It's been a while since I debugged the VCO, so I don't recall exactly which joints were shorting. But I can give you some places that are potential spots for trouble. There are some vias on the board that in addition to being very tiny, are extremely close to solder pads. For example, check the via between R15 and R14. Two more places are between R33 and R36 ( on the right side looking at the back of the PCB ) and between R56 and D3 (left side). If you accidentally bridged one of these vias to a nearby solder pad, the VCO won't work right. Synthrotek does provide a zoomable pic of the front side of the PCB. You'll be looking at the solder side. I recommend using a magnifying glass and your multimeter to check for possible shorts. The vias are so close to the solder pads, it's really difficult to spot a short with the naked eye. There are some other places for potential shorts, but these 3 spots will get you off to a good start so you can check other areas.

While you're at it, check the vias around both pads of C4. Again, very very tiny and very very close to the pads.

This VCO was easily the densest PCB I've every worked on. I went thru several rounds of debugging to fix this. I fried an IC and a few diodes in the process. It was incredibly satisfying to find the problems and fix them. It also prepared me for future MST builds. ( so far, the VCO was the most crowded )

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Post by Hossymandias » Sun Apr 23, 2017 8:38 am

I "finished" my Synthrotek Dual Envelope two days ago (sourced my own parts from Tayda) and had the exact same issues as described by the OP: red LED flashed once on power-up, neither channel fired, output pot attenuated voltages but essentially non-functioning.

I was discouraged to read through this thread and find no real solution, but when I reheated and flowed solder on all IC sockets and male headers...viola! It works perfectly except that I think the green channel LED is blown. That channel works, except the LED doesn't light. I'll replace and I expect the unit will work as advertised.

I hope this is helpful to those who have a similar problem and are afraid there is a more specific problem with parts or ICs or something. Cheers!

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Hint for fitting U2/U4

Post by ground_state » Mon May 08, 2017 11:03 am

Do the socket pins like so:
Image
Then note that the IC pins are quite narrow compared to the slots in the sockets. Insert U2 as far forward in the socket as possible; U4 likewise but as far back.
Works quite well, although they are pretty much touching.
I don't have a pic of the finished board with me atm, but I'll upload one later.
EDIT:
Pics or it didn't happen ;)
Image
Last edited by ground_state on Wed May 10, 2017 8:08 pm, edited 1 time in total.

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Issue with 2nd channel AD/ASR switch

Post by ground_state » Mon May 08, 2017 11:15 am

Yeah, self-congratulation on a good build aside, $subject. It's basically a power switch :eek: i.e. turns the unit off... Everything else works as it's supposed to. I examined the traces/solder joints as best I could, and continuity testing for the switch itself shows that at a minimum it works the same as the one on channel 1...
I can live without it, but it's puzzling.

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Post by creativechaoscom » Tue May 09, 2017 10:32 pm

Hi,

I can add another failed build to the list with a twist. Mine is working 50% in that the top AD/ASR seems to be working fine, the bottom one however does nothing.

I already sent some pics of my build to Synthrotek to see if they find something and they suggested to check for blown diodes. So far everything checks out normal.

George: thanks for posting some more details in terms of which voltages should be where. I suggested to Synthrotek to have the build instructions in stages with test points along the way (something I got used to in the ham radio world of kits).

Any additional pointers are welcome.

I also built the VCA, VCLPF, Stereo Mixer, and VCLFO. All are working fine.

Cheers,
Michael[/img]

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Re: Hint for fitting U2/U4

Post by Mr_Mojo_Risin » Mon Jun 05, 2017 8:28 am

ground_state wrote:Do the socket pins like so:
Then note that the IC pins are quite narrow compared to the slots in the sockets. Insert U2 as far forward in the socket as possible; U4 likewise but as far back.
Works quite well, although they are pretty much touching.
I was able to get my MST Dual AD/ASR Envelope module working just fine on the first try.
I'm using the most recent PCB version which was purchased on 05/28/2017.
This PCB rev. differs from the images shown at the Synthrotek website.
The TL074CN and CD4011BE IC's are from Tayda.


Luckily, I read this thread before starting so I was able to avoid the pitfalls re: the spacing problem between IC #U2 and #U4.
I applied a similar strategy as used by Muffwiggler user "ground_state" for the IC sockets.
Since I use machine tooled sockets, they tend to break if you bend the pins so instead, I slightly tilted up the socket used for IC #U2 where it butts up against IC #U4.
After doing this, there's still enough clearance to avoid the PCB above and there is also enough room below the solder pads for the socket pins to stick out for rigid solder connections.

This newer PCB rev. doesn't seem to have any issue other than lack of spacing between IC #U2 and #U4. Works great!

Image

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Post by Hossymandias » Wed Sep 20, 2017 5:41 am

Well, I'm having more trouble with this module. I had gotten it working to the point that both channels were firing, but the top LED didn't flash. So tonight I took it apart and went over all solder joints. Now, it doesn't work at all, except that on power up, both LEDs flash, then nothing.

Tell me if I'm wrong, but I assume I have created a solder bridge and/or a short to ground?

:bang:

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Post by StudentsOfTheFuture » Wed Sep 20, 2017 3:12 pm

Have you tested any signal w/ it like that?

Granted it looks bad, and could be - but mine was stuck like that for a bit during troubleshooting, having to do with how the jacks were set to cycle.

I'm blanking on what exactly I did but I think checking socket joints and plugging and unplugging cables into the gates helped. Maybe mode switches as well?

As for bridges and shorts, some of the best advice I got was to scrub HARD with some isopropyl and a brush cause flux and tiny solder strands can mess up your day. You'll also get a good look at any questionable joints this way.

If it's still not working, post some pictures? Maybe it's something obvious.
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Post by Hossymandias » Wed Sep 20, 2017 7:44 pm

Thank you studentsofthefuture, it's working perfectly now. I cleaned out the gates, cleaned the back of the board, and it's firing on all channels. I think I must have had a tiny bridge on the back of the board. Thanks for keeping me calm and logical. 8-)

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