Help me troubleshoot Toppobrillo 281

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wendallsan
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Help me troubleshoot Toppobrillo 281

Post by wendallsan » Wed Jan 29, 2020 2:38 pm

Hi all,

After a college quarter of working closely with a Buchla 200, I decided I needed some Buchla-esque function generators. The best match I found was the Toppobrillo 281. I have built 4 of these and am seeing the same results in all 4 of them. In short, none of them are working (yet) and one gets a hot chip on it when it is plugged in, to boot. I'll take a good look at that one 'hot' module, as finding the problem should be pretty easy if I compare it side-by-side with one of my 'non hot' boards. But other than that, here is what I'm seeing so far in all of them:

No signal is generated when provided a trigger in either AR or AD mode, or in oscillator mode. I'm guessing that since this is a clone you need to flip the function generator into trigger mode and back into osc mode to get the oscillation started (just like the Buchla 200e module!), but this doesn't seem to be working either. The LED's are not lighting up and no signal is being output.

:deadbanana:

I'm hoping that whatever is wrong is consistent, so I'm starting with one of the 'non-hot' modules. I've included photos of the boards below. Please let me know any initial thoughts you may have or let me know which IC's you'd like readings from. With luck, if I can get one working I can get the rest going as well.

I've checked this particular module over and the IC's have been confirmed to be installed in the proper direction, transistors, diodes, and polarized caps also look promising. Solder joints have been looked at under magnification and one missed solder joint has been fixed.

Many thanks for any assistance! :sb:

Top Front
Top Back
Bottom Front
Bottom Back

I can't wait to get these and my quad lowpass gates going together! Hello Buchla-land!

:buchla:
Student at Evergreen State College's "Advanced Electronics In Music" for the 2019-2020 school year. Built a Roland System 700 clone out of Pharmasonic PCB's. Currently building or troubleshooting a DJ Thomas White Quad Lowpass Gate, a Barton Bytewise Operator + Expander, and a Pharmasonic SYS-700 702 Oscillator.

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Re: Help me troubleshoot Toppobrillo 281

Post by guest » Wed Jan 29, 2020 3:28 pm

looks like a missed solder joint on one of the opamps (righthand side of bottom_back image).

do all the chips have +/-12V and gnd on the appropriate powersupply pins?
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Re: Help me troubleshoot Toppobrillo 281

Post by guest » Wed Jan 29, 2020 3:41 pm

actually, i see 2 more IC pins that arent soldered. id reccomend going over all the joints again.
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Re: Help me troubleshoot Toppobrillo 281

Post by squarewavesurfer » Wed Jan 29, 2020 6:18 pm

The smd caps look like they could use a reflow. You might need more heat and/or flux as there are a few spots that look like cold solder joints.

Also there is an op amp near the bottom left of the "bottom back" pcb that doesn't appear to be properly seated in the socket.

Like others say, check for poor solder joints and bridges with a magnifying glass then test the suspect connections with a multimeter for continuity. I like to get a picture of the unpopulated pcb and compare side by side. It's easy to hide the proper IC orientation under a reversed socket.

The "hot" board is could potentially be a solder bridge or a reversed ic or voltage regulator. If so you may need to swap out the damaged parts.
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Re: Help me troubleshoot Toppobrillo 281

Post by wendallsan » Wed Jan 29, 2020 8:30 pm

Hi all, thanks for the assistance and for pointing out the bad soldering points. I've touched these up and believe I got them all, as well as reflowed the SMD caps.

I've checked the IC's and the 4001's and 4016 don't seem to have any negative voltages going into them. I pulled up datasheets and am guessing that the "VSS" pins are the ones I'm interested in. It looks like each of these IC's is 0V, and I'm guessing I should be expecting ~-11V or so there, like I am seeing at pin 1 of the LM13700 and pin 4 of all the TL062's.

Here is an updated shot of the bottom of that board, with soldering joints fixed.

https://dansteeby.com/wp-content/upload ... back-2.jpg

I wish I had scanned the blank PCB's prior to populating them, but I was too eager. :despair:

I'll try to trace things from the negative voltage input to these pins as soon as I have a chance to do so. I'll post my tracing attempts if I can't figure it out. Many thanks again for your help so far!
:sb:
Student at Evergreen State College's "Advanced Electronics In Music" for the 2019-2020 school year. Built a Roland System 700 clone out of Pharmasonic PCB's. Currently building or troubleshooting a DJ Thomas White Quad Lowpass Gate, a Barton Bytewise Operator + Expander, and a Pharmasonic SYS-700 702 Oscillator.

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Re: Help me troubleshoot Toppobrillo 281

Post by guest » Wed Jan 29, 2020 8:59 pm

those are digital ICs, so will just have 0V on pin7.
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Re: Help me troubleshoot Toppobrillo 281

Post by wendallsan » Thu Jan 30, 2020 10:55 am

Alright, something new learned (no negative voltage needed for digital IC's)! :sb:

I've taken voltage readings of the IC's on the board, here is a pic identifying the IC's by letter assignment:

Image

A
1 -10.75
2 0
3 0
4 0
5 0
6 -11.71
7 0
8 0
9 0.02
10 0
11 11.81
12 0
13 0
14 0
15 0
16 -10.43

B
1 -0.02
2 0
3 0
4 -11.71
5 0
6 0
7 0
8 11.81

C
1 0.14
2 0.13
3 0.13
4 0.19
5 0
6 0
7 0
8 0
9 0
10 0
11 0
12 0
13 0
14 9.71
15 9.71
16 9.71

D
1 -0.01
2 0
3 0
4 -11.71
5 0
6 0
7 0
8 11.81

E
1 -11.00
2 0.31
3 0
4 -11.71
5 7.49
6 0
7 11.10
8 11.82

F
1 10.13
2 0.04
3 0
4 9.71
5 0
6 -0.64
7 0
8 -0.02
9 -0.64
10 9.71
11 0
12 9.70
13 9.70
14 9.71

G
1 9.71
2 0.04
3 0.02
4 9.70
5 0
6 -0.64
7 0
8 -0.04
9 -0.64
10 0
11 0
12 9.70
13 9.70
14 9.71

H
1 -10.99
2 0.31
3 0
4 -11.71
5 7.55
6 0
7 11.14
8 11.82

I
1 -11.64
2 -0.46
3 -0.46
4 -11.71
5 -11.64
6 0
7 11.82
8 0
Student at Evergreen State College's "Advanced Electronics In Music" for the 2019-2020 school year. Built a Roland System 700 clone out of Pharmasonic PCB's. Currently building or troubleshooting a DJ Thomas White Quad Lowpass Gate, a Barton Bytewise Operator + Expander, and a Pharmasonic SYS-700 702 Oscillator.

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Re: Help me troubleshoot Toppobrillo 281

Post by guest » Thu Jan 30, 2020 11:41 am

its going to be tough to help without a schematic, but hopefully this is close:
http://electro-music.com/wiki/pmwiki.ph ... nGenerator

first off, does it respond to any inputs on any of the modes? do the knobs or switches change the output in any way? what voltage is the ouptut stuck at (if its not changing)?

next, apply a gate to the input (be sure to put it in AR mode), and then follow that signal. it looks like it goes to an opamp, then to some NORs acting as a latch, and then another opamp.
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Re: Help me troubleshoot Toppobrillo 281

Post by pre55ure » Thu Jan 30, 2020 11:45 am

guest wrote:
Thu Jan 30, 2020 11:41 am
its going to be tough to help without a schematic, but hopefully this is close:
http://electro-music.com/wiki/pmwiki.ph ... nGenerator
Thats more than close, that is the correct schematic. :party:

Also - someone made a panel pcb for these?!?!
When did that happen?
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Re: Help me troubleshoot Toppobrillo 281

Post by wendallsan » Thu Jan 30, 2020 1:04 pm

guest wrote:
Thu Jan 30, 2020 11:41 am
first off, does it respond to any inputs on any of the modes? do the knobs or switches change the output in any way? what voltage is the ouptut stuck at (if its not changing)?
I'm getting 0V output on both function generators, regardless of the mode it is in or how the attack and release pots are tweaked. It seems like the only 'function' going on here is 'multiply by zero' :hihi:
next, apply a gate to the input (be sure to put it in AR mode), and then follow that signal. it looks like it goes to an opamp, then to some NORs acting as a latch, and then another opamp.
This didn't go very far! I can trace a gate signal into the jack and to test points on the top board for both gate inputs (labelled "TG A" and "TG B"), but I cannot see where these signals going anywhere beyond the test points! I don't see any other traces headed from these jacks (or at least the pin the jack that has the trigger signal on it) that go anywhere but to these test points, and nowhere else. I checked all the pins on the top board that go to the bottom board, and don't see any signals there, so I don't think the trigger is making it to the opamp as shown in the schematic. The schematic doesn't clearly identify which IC this op amp is, so I'm not able to try to trace backwards from the opamp to the trigger.

Here is my trace:

Image

Is this supposed to be a '2 pin header' that goes between boards? I didn't see anything about a 2 pin header in the BOM or elswhere in the build notes, but they DO line up with empty holes on the bottom board below it. I checked these points on the top board and am not seeing the trigger signal there, so this may not be related to my gate tracing issue.

Image
Student at Evergreen State College's "Advanced Electronics In Music" for the 2019-2020 school year. Built a Roland System 700 clone out of Pharmasonic PCB's. Currently building or troubleshooting a DJ Thomas White Quad Lowpass Gate, a Barton Bytewise Operator + Expander, and a Pharmasonic SYS-700 702 Oscillator.

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Re: Help me troubleshoot Toppobrillo 281

Post by emmaker » Thu Jan 30, 2020 1:29 pm

pre55ure wrote:
Thu Jan 30, 2020 11:45 am
Thats more than close, that is the correct schematic. :party:
That's for the single version of the 281. The dual version shares chips and you won't find that in that schematic. You're going to pin numbers on chips that won't match up.

This is a great example of doing a project which is focused on making the build easy and trouble shooting it a major pain.

Jay S.

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Re: Help me troubleshoot Toppobrillo 281

Post by guest » Thu Jan 30, 2020 1:45 pm

it looks like all 9 headers might match up to the bottom board, except only 1 pin is used in all but 3 of those headers????
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Re: Help me troubleshoot Toppobrillo 281

Post by guest » Thu Jan 30, 2020 1:50 pm

i just checked the synthcube BOM, and it lists 9x 2 pin headers, with 1 pin removed on them. so you should connect all of them.
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Re: Help me troubleshoot Toppobrillo 281

Post by wendallsan » Mon Feb 10, 2020 10:14 am

My 2-pin headers arrived and I was able to finish these modules this weekend, along with a comb filter. Amazing how they suddenly worked fine once the 10-or-so connections between the boards that weren't there were added. :sb:

Looking forward to making some Buchla-esque sounds, especially when I finally finish my quad lowpass gate!

:buchla:

Image

Once again, thanks for the assistance in identifying all those remaining holes on the boads were not test points and actually had to be connected. The modules' two boards are definitely well held together with all these headers (13 headers in all!). This works out well, since there are no holes on the top board to screw standoffs into. This must be what happens when someone builds a pots-and-jacks board to go with an existing circuit board that wasn't originally built with the second board in mind!

Image
Last edited by wendallsan on Mon Feb 10, 2020 2:35 pm, edited 2 times in total.
Student at Evergreen State College's "Advanced Electronics In Music" for the 2019-2020 school year. Built a Roland System 700 clone out of Pharmasonic PCB's. Currently building or troubleshooting a DJ Thomas White Quad Lowpass Gate, a Barton Bytewise Operator + Expander, and a Pharmasonic SYS-700 702 Oscillator.

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Re: Help me troubleshoot Toppobrillo 281

Post by wendallsan » Mon Feb 10, 2020 10:16 am

Also the one board with the 'hot chip' problem was an easy fix. I found two unsoldered solder points, and the hot chip in question a (TL062) had cracked and was ruined. A couple spots of solder and a new chip in the socket, and we are good to go!
Student at Evergreen State College's "Advanced Electronics In Music" for the 2019-2020 school year. Built a Roland System 700 clone out of Pharmasonic PCB's. Currently building or troubleshooting a DJ Thomas White Quad Lowpass Gate, a Barton Bytewise Operator + Expander, and a Pharmasonic SYS-700 702 Oscillator.

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Re: Help me troubleshoot Toppobrillo 281

Post by guest » Mon Feb 10, 2020 12:58 pm

glad to hear theyre up and running!
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Re: Help me troubleshoot Toppobrillo 281

Post by elmegil » Sun Feb 16, 2020 12:03 am

pre55ure wrote:
Thu Jan 30, 2020 11:45 am
Also - someone made a panel pcb for these?!?!
When did that happen?
STILL WAITING FOR ANSWER :-)

Seriously, I have a couple of the 281's lying around (I *think* the duals) and would LOVE a panel PCB.

Actually never mind, I just dug them up and they're the singles.

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Re: Help me troubleshoot Toppobrillo 281

Post by synthetek » Sun Feb 16, 2020 6:30 am


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