having a problem in envelope (gate) testing phase

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cchocjr
 
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Joined: Sun Mar 05, 2006 10:57 am

having a problem in envelope (gate) testing phase

Post by cchocjr »

When following the directions for testing the envelope in the fab manual (hook up main power supply, jumper from R146 to R3, test voltage at north side of D35 with jumper connected and disconnected) I get about 11.8 regardless of whether or not the jumper from 146 to 3 is connected. I've followed all the testing instructions up to this point (oscilliscope-less methods) and have had satisfactory results. Before testing the envelope, however, I went ahead and put in the components for the VCA. It was when testing this section, and not getting a gated note, that I went back to the envelope to test it appropriately.

I've went over the envelope components several times, verifying polarity where appropriate, tested continuity where it should be and where it shouldn't, etc....etc...and I'm still getting the same voltage readings a D35 whether or not the gate is activated.

Have any of you intrepid builders out there come across this problem? Any ideas on how to proceed? I've double and triple checked the orientation of the capacitors and the transistors, and I was pretty thorough in checking out the resistors via MM before placing them in the board. For the time being, I'm just going to resolder all the parts in the envelope section just to make sure there isn't a cold joint anywhere.

Many thanks for your time.

guest
 
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Joined: Fri Feb 17, 2006 5:35 am

Post by guest »

measure the voltage at the juncture of
r146 and r144
it should be 0v

measure the voltage at the juncture of
r142 and r143
it should be 12v

measure the voltage across r145
it should be 0v

double check the orientation of q36 and q37

asmodee
 
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Joined: Tue Feb 14, 2006 9:25 pm

Post by asmodee »

Are you sure that you're connecting the gate input to the correct side of R146?

Follow the schematic here http://ladyada.net/make/x0xb0x/files/mainboard_beta.png

Start in the bottom left, this is the gate input into R146. Follow it to D35 as these are the components that you should primarily be concerned with. Specifically look for solder bridges, test continuity and resolder all joints to ensure you don't have any cold joints. Perhaps you have one of the 536 transistors in wrong as they are not as easily identifiable as the 733s in terms of their orientation.

When you do not have R3 connected to R146 what is the voltage on R3? When it is connected what is the voltage on R3? did you do any tests before the VCA like the PSU, VCO and VCF tests?

cchocjr
 
Posts: 73
Joined: Sun Mar 05, 2006 10:57 am

Post by cchocjr »

asmodee wrote:Are you sure that you're connecting the gate input to the correct side of R146?
Pretty sure. I'm not in front of the x0x at the moment, so I will double check. However, after finishing the VCA, testing it, and finding out that something was awry, I went back to the envelope and tested it accordingly. I was thrown off a bit by the "test exposed side of R3" part of the instructions, as, to the best of my recollection, there were no specific instructions regarding this particular component. But, to be on the safe side, I de-soldered R3 and placed it back so that it mirrored the illustration in the fab manual.

asmodee wrote:Start in the bottom left, this is the gate input into R146. Follow it to D35 as these are the components that you should primarily be concerned with. Specifically look for solder bridges, test continuity and resolder all joints to ensure you don't have any cold joints. Perhaps you have one of the 536 transistors in wrong as they are not as easily identifiable as the 733s in terms of their orientation.

When you do not have R3 connected to R146 what is the voltage on R3? When it is connected what is the voltage on R3? did you do any tests before the VCA like the PSU, VCO and VCF tests?
I will try this as soon as possible. During the several times I've sat down and tried to troubleshoot this, I've checked, double-checked, and triple-checked the orientation of the transistors; I've checked and double checked that the appropriate parts were used (for the resistors, I checked all the pertinent ones against the visual data provided in the envelope section of the fab manual, and, also, I was pretty thorough about testing the ratings of the resistors before placing them, unless it was obvious that it was the correct one after cross-checking the part number with the prep. section's BOM--specifically, the number of the particular part supplied.)

And yeah, before getting too a little too ahead of myself be going on to the VCA before adequately testing the gate function of the envelope, I had tested the PSU, VCO, and VCF after each section was built out.

I will perform the tests you folks have very kindly suggested and get back with you. Aarrgh, this is aggravating--but not unbearable. I'm sure it just comes with the territory.

And anyway, anything worth having must be worked for. :D

cchocjr
 
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Post by cchocjr »

Also, I have already resoldered the vast majority of the envelope's components, though not methodically enough to rule out a cold joint. I am pretty confident, though, that there are no bridges, as I've done a good bit of continuity testing--and even more visual inspection of both sides of the board with the aid of my light and magnifying glass.

cchocjr
 
Posts: 73
Joined: Sun Mar 05, 2006 10:57 am

Post by cchocjr »

guest wrote:measure the voltage at the juncture of
r146 and r144
it should be 0v

measure the voltage at the juncture of
r142 and r143
it should be 12v

measure the voltage across r145
it should be 0v

double check the orientation of q36 and q37
V at juncture of R146 and R144 is 1.15

V at junctre of R 142/3 is 0

V across (?) R 145 is 0, although the 'east' lead yields a reading of 11.8

Q 36/7 are oriented properly

Does this mean anything to anyone?

Thanks

cchocjr
 
Posts: 73
Joined: Sun Mar 05, 2006 10:57 am

Post by cchocjr »

asmodee wrote:Are you sure that you're connecting the gate input to the correct side of R146?

Follow the schematic here http://ladyada.net/make/x0xb0x/files/mainboard_beta.png

Start in the bottom left, this is the gate input into R146. Follow it to D35 as these are the components that you should primarily be concerned with. Specifically look for solder bridges, test continuity and resolder all joints to ensure you don't have any cold joints. Perhaps you have one of the 536 transistors in wrong as they are not as easily identifiable as the 733s in terms of their orientation.

When you do not have R3 connected to R146 what is the voltage on R3? When it is connected what is the voltage on R3? did you do any tests before the VCA like the PSU, VCO and VCF tests?
I traced from R146 to D35, and there was continuity where it was supposed to be, and no continuity where it wasn't supposed to be. As an aside, it turns out that I had bridged D35 and 36 (or is it 34, whatever the one next to 35 is). I couldn't see a bridge anywhere, even with my magnifying glass, but I went ahead and removed the two diodes, vacummed out the solder, and put in two new diodes. I had hoped that this was it, but alas, the same results.

FWIW. the voltage on R3 is 5.33 with or without it being jumped to R146.

Thanks for your consideration.

cchocjr
 
Posts: 73
Joined: Sun Mar 05, 2006 10:57 am

Post by cchocjr »

This is sort of an aside, but is there anyway to test the resistors after they have been soldered in place. I've visually inspected all of them, but it wouldn't hurt to cross-check them against their supposed resistance. I REALLY don't want to desolder all of them to do it, but if push comes to shove...

Thanks again.

guest
 
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Joined: Fri Feb 17, 2006 5:35 am

Post by guest »

the voltage readings are very confusing
were they all taken with the gate drive off

to measure the voltage across an element
you place on probe on one side
and the other probe on the other side
and this gives the potential difference
between those two points

the rest of the voltage readings
should be referenced to ground


im not sure which lead is the east lead of r145
but one end of that resistor is tied to ground
so if there is 0v across it
the other side should be at ground as well
so it would be impossible for it to be at 11.8v
perhaps the solder joint to ground is bad
you can measure the resistance between
that lead and ground to check it

it is also odd that there is 1.15v at
the juncture of r144 and r146
what are the voltage drops across both of those resistors

it is also odd that there is 0v at
the juncture of r142 and r143
the only way this could happen is if
there is a short to ground from that point
can you measure the resistance
from that point to ground

cchocjr
 
Posts: 73
Joined: Sun Mar 05, 2006 10:57 am

Post by cchocjr »

guest wrote:the voltage readings are very confusing
were they all taken with the gate drive off

to measure the voltage across an element
you place on probe on one side
and the other probe on the other side
and this gives the potential difference
between those two points

the rest of the voltage readings
should be referenced to ground


im not sure which lead is the east lead of r145
but one end of that resistor is tied to ground
so if there is 0v across it
the other side should be at ground as well
so it would be impossible for it to be at 11.8v
perhaps the solder joint to ground is bad
you can measure the resistance between
that lead and ground to check it

it is also odd that there is 1.15v at
the juncture of r144 and r146
what are the voltage drops across both of those resistors

it is also odd that there is 0v at
the juncture of r142 and r143
the only way this could happen is if
there is a short to ground from that point
can you measure the resistance
from that point to ground
Alright; here are some further test data.

voltages with gate connected
- V across R145 = 11.8
- V @ juncture of R144/6 = 8.9
- V @ juncture of R142/3 = 0

voltages with gate DISconnected
- V across R145 = 11.8
- V @ juncture of R144/6 = 0
- V @ juncture of R142/3 = 0

Resistance between R145 and ground = 10K
Resistance between juncture of R142/3 and ground = no reading

Resistance across R144 = 10K
Resistance across R146 = 22K

I'm going to start a BANNED of checking the resistors resistances and resoldering each component; ugh.

If anyone has any further suggestions, hints, etc...they are insanely welcome.

Thanks

cchocjr
 
Posts: 73
Joined: Sun Mar 05, 2006 10:57 am

Post by cchocjr »

Alright. I just resoldered all of the parts in the envelope phase--part by part. Still, I get ~12V at D35 regardless of whether or not R146 is connected to R3. Is there any possibility that the problem might lie in an 'area' other than the envelope?

I'm sure of the connection between R3 and R146, so that is not the culprit. Is there any way that one of the transistors is bad?

I am trying to be of good cheer, but I really don't want to press on until the friggin' gat works.

guest
 
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Joined: Fri Feb 17, 2006 5:35 am

Post by guest »

can you try removing r143 and see if the
problem persists

the r144 and r146 juncture should never go
above .6v
if it does there is a good chance q37 is blown

the same goes for q36
its base shouldnt drop more than .6v below
the 12v supply

what voltage are you applying to r146 to test the gate

cchocjr
 
Posts: 73
Joined: Sun Mar 05, 2006 10:57 am

Post by cchocjr »

guest wrote:can you try removing r143 and see if the
problem persists

the r144 and r146 juncture should never go
above .6v
if it does there is a good chance q37 is blown

the same goes for q36
its base shouldnt drop more than .6v below
the 12v supply

what voltage are you applying to r146 to test the gate
Removed R143; the voltage to the north side of D35 dropped to 0, with or without R146 connected to R3. I'll probably go ahead and try putting in new transistors, but all advice is still insanely welcome.

Thanks yet again.

evilxsystems
 
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Joined: Thu Jul 07, 2005 10:23 pm

Post by evilxsystems »

yeah I blew q37 (and my microcontroller) by sending voltage from the wrong side of r3...twenty some volts instead of twelve...while testing the gate...

cchocjr
 
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Joined: Sun Mar 05, 2006 10:57 am

Post by cchocjr »

evilxsystems wrote:yeah I blew q37 (and my microcontroller) by sending voltage from the wrong side of r3...twenty some volts instead of twelve...while testing the gate...
I think that I did the same freakin' thing, man. The first time I test the gate, I attached a clip to R3--I didn't think it mattered which side, and the fab manual didn't specify--other than "the exposed side," even though during the 'prep' phase, when this resistor was installed, it was not made clear that it had to go in any particular way. It could be a practice so common though that I ought to have known.

Any way, long story short, I replaced Q37, and now I get 11.8 volts at R35 with the gate engaged, and nothing when it is disengaged, which is close enough for me!

Now I'm just going to have to figure out where to track down one of the 'rare' transistors that I am now short on--weak.

On to testing the VCA. Thanks for everyone's help...it was dearly needed, as I was getting pretty pissed.

Thanks again.

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