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PostPosted: Fri Aug 13, 2021 8:30 pm 
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Hey, guys! I really appreciate all the help! After having problems with the first version of the Brownface Tremolo, I received the updated kit and finally had a chance to assemble it. The new version sounds MUCH better, but...

The DEPTH control seems to work the way it's supposed to, but the speed seems to be fixed at a medium clip (the SPEED control pot does nothing). I made sure the solder points had a good bead, and verified the resistance is correct across the sweep of the pot, but the speed is still fixed at about what I assume is the middle of the range.


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Brownface Tremolo speed 1.jpg
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PostPosted: Mon Aug 16, 2021 10:42 am 
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The speed is controlled by a resistance to ground. The more this resistance increases, the slower the speed and vice versa. If you look at the schematic, you can see that this resistance is made up of the C100k speed pot and a 1k8 resistor. The 1k8 resistor acts as the maximum speed limiting resistor. The C100k pot is wired as a rheostat (a single variable resistance that only utilizes 2 of its pins rather than utilizing all 3 pins for a voltage divide), so not taking component tolerance into consideration, you should have a variable resistance of 1k8 ohms ~ 102k ohms.

I would assume you have some sort of short that is not allowing the speed pot to be a variable resistor, and has turned into a fixed resistor. Perhaps it's damaged. Often a tiny piece of wire strand clipping will get inside the pot and short it out. Maybe it's a solder short. Use your multimeter to measure resistance between the left side eyelet of the 1k8 resistor and ground. You should see the resistance change between 1k8 and 102k as you turn the speed pot, but I suspect you'll see that it doesn't change.

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PostPosted: Sat Aug 21, 2021 11:30 am 
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I checked ground to the 1k8 resistor, and, as suspected, it stays at 11.8 through the whole sweep of the speed control pot. I verified the solder points are all good. What now?


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PostPosted: Sat Aug 21, 2021 12:24 pm 
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MojaveJohnson wrote:
...it stays at 11.8 through the whole sweep of the speed control pot.

Did you enter that value correctly??

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PostPosted: Sun Aug 22, 2021 9:32 pm 
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duhvoodooman wrote:
MojaveJohnson wrote:
...it stays at 11.8 through the whole sweep of the speed control pot.

Did you enter that value correctly??


Sorry, I should have specified I had the multimeter set to 200K ohm, but yes, that's what it read.


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PostPosted: Mon Aug 23, 2021 10:29 am 
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Hmm, OK, but that value doesn't seem to make a whole lot of sense. I would suggest these follow-up actions:

The first thing I would do would be to clean off the solder joints on the Speed pot so that we can visually inspect those joints and the PCB trace connections to them. Right now, the pooled up and partially discolored solder mask residue (see cropped image below) makes it very difficult to see what's going on there. I would use the blade of a small flat-head screwdriver to gently scrape the solder mask away around the pot joints and brush off the loosened residue with a toothbrush or other small, stiff-bristled brush. Once that area is cleaned up, please post a new photo or two so that we can visually inspect the connections.

Next, take a series of resistance measurements across the pot to determine its functionality. Disconnect power from the pedal and place one of your meter probes into one of the corner screw bosses--this is your ground connection. With the Speed pot turned all the way CCW, take resistance readings by placing the other meter probe:

  • On the left lug solder joint
  • On the middle lug solder joint
  • On the right lug solder joint

Since the middle and right lugs are connected by a short PCB trace, they should give the same resistance reading, equal to the approximate resistance rating of the pot (~100 Kohms). The left lug is connected to ground and should therefore show a resistance of ~zero.

If that all pans out, then turn the Speed pot to its midpoint and measure the resistance at the right lug. On my BT, that value is ~16 Kohms. The turn the pot all the way CW and repeat the measurement. Should be nearly zero resistance, or a couple of ohms at the most.

Please post all your results here.

Attachment:
BHT_speed_pot_joints.jpg
BHT_speed_pot_joints.jpg [ 61.18 KiB | Viewed 7638 times ]

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PostPosted: Sun Aug 29, 2021 3:11 pm 
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I cleaned up the connections as best as I could, and got a couple more pics with less glare. I wasn't able to get connectivity on any of the screw bosses, but I did get connectivity on the PCB ground connection next to the SPEED pot.

With the pot turned full CCW, and my multimeter set to the 200K ohm range (directions in relation to the top of the pot)
L - 10.0
M - 10.0
R - 0.1

With the pot in the middle position:
L - 1.7
M - 1.7
R - 0.1

With the pot full CW:
L - 10.0
M - 0.5
R - 0.5


Attachments:
Brownface Tremolo speed 4.jpg
Brownface Tremolo speed 4.jpg [ 363.21 KiB | Viewed 7558 times ]
Brownface Tremolo speed 3.jpg
Brownface Tremolo speed 3.jpg [ 427.18 KiB | Viewed 7558 times ]
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PostPosted: Sun Aug 29, 2021 6:14 pm 
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Those results don't all make sense, but it sure looks like you have a C10K pot installed there rather than a C100K! Suggest that you check the label on the top side of the pot.

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PostPosted: Sun Sep 05, 2021 12:58 pm 
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duhvoodooman wrote:
Those results don't all make sense, but it sure looks like you have a C10K pot installed there rather than a C100K! Suggest that you check the label on the top side of the pot.


My multimeter is set to the 200K ohm range, so 10.2 means 102K ohms.

The pot is a C100K, according to the imprint on the top side. It's the one that was provided with the kit.


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PostPosted: Tue Sep 07, 2021 11:30 am 
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MojaveJohnson wrote:
duhvoodooman wrote:
Those results don't all make sense, but it sure looks like you have a C10K pot installed there rather than a C100K! Suggest that you check the label on the top side of the pot.


My multimeter is set to the 200K ohm range, so 10.2 means 102K ohms.

The pot is a C100K, according to the imprint on the top side. It's the one that was provided with the kit.


With your probes between the left eyelet and center eyelet (from the top of the PCB) of the speed pot, can you adjust the resistance from 0 to 102k?

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PostPosted: Fri Sep 10, 2021 7:54 am 
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Yes, but in the middle of the sweep it also read 102K ohms.


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PostPosted: Fri Sep 10, 2021 10:57 am 
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MojaveJohnson wrote:
Yes, but in the middle of the sweep it also read 102K ohms.


It's not a linear taper, so you shouldn't expect it to read 51k in the middle.

Now can you measure an adjustable resistance between lug 3 (left most eyelet again) and R23 1k8 resistor. Measure from the side of the resistor that is closest to the center lug of the pot. Now you should have a resistance between 1k8 and 102k.

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PostPosted: Sun Sep 12, 2021 4:34 pm 
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It reads 1K8 no matter where the pot is set.


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PostPosted: Mon Sep 13, 2021 11:32 am 
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MojaveJohnson wrote:
It reads 1K8 no matter where the pot is set.



There are only two possible explanations for why you would get that result. The first is that the trace on the top of the PCB that connects lugs 2 and 1 of the speed pot to the right side of the 1k8 resistor is broken and that right side pad of the 1k8 resistor is shorted to ground. Or the other explanation is that you aren't taking readings from the correct test points.

If you look at the schematic, you can see that the speed is controlled by the resistance between the C15/16/17/18 junction and ground. The larger the resistance, the slower the speed. The smaller the resistance, the faster the speed. The 1k8 resistor is there as a limiting resistor. It can't go any faster than 1k8 otherwise it will cut out. According to your measurements, the 1k8 resistor is somehow bypassing the speed pot altogether and going straight to ground.

I'm not sure how you could physically accomplish this accidentally, but it would explain why your LFO is working but not able to vary its speed. Would you say the speed it's stuck in is "fast"?

Are you sure you are measuring from the left side pad of the 1k8 resistor and the leftmost pad of the speed pot?

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PostPosted: Tue Sep 14, 2021 10:32 pm 
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byoc wrote:
MojaveJohnson wrote:
It reads 1K8 no matter where the pot is set.



There are only two possible explanations for why you would get that result. The first is that the trace on the top of the PCB that connects lugs 2 and 1 of the speed pot to the right side of the 1k8 resistor is broken and that right side pad of the 1k8 resistor is shorted to ground. Or the other explanation is that you aren't taking readings from the correct test points.

If you look at the schematic, you can see that the speed is controlled by the resistance between the C15/16/17/18 junction and ground. The larger the resistance, the slower the speed. The smaller the resistance, the faster the speed. The 1k8 resistor is there as a limiting resistor. It can't go any faster than 1k8 otherwise it will cut out. According to your measurements, the 1k8 resistor is somehow bypassing the speed pot altogether and going straight to ground.

I'm not sure how you could physically accomplish this accidentally, but it would explain why your LFO is working but not able to vary its speed. Would you say the speed it's stuck in is "fast"?

Are you sure you are measuring from the left side pad of the 1k8 resistor and the leftmost pad of the speed pot?


I don't know how to read a schematic, but I was definitely reading from the left lug (further from the side of the PCB) and the side of the resistor you specified ("closest to the center lug of the speed pot"). As for the trace between the right and center lugs, I really can't tell for sure (and I can't get a decent enough image of it), but I was wondering if it was broken. I couldn't tell if it was an illusion of the melted coating on the PCB. If that's the case, couldn't I just solder a jumper between the lugs to close the connection?

As for the speed, I'd say it's stuck somewhere in the middle (maybe around 80-90 BPM?). It's actually a very usable and musical speed, but I need it adjustable for different songs.


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PostPosted: Wed Sep 15, 2021 2:21 pm 
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Try removing the speed pot and 1k8 resistor completely. Does the pedal still work?

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PostPosted: Fri Oct 29, 2021 4:35 am 
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So.... what happened!? Does it work now?


Also, Hey Keith, What kind of Lunatic Mod can I play around/experiment with, to get the speed down to the gnarliest slowest, stupidest sssssssslowest speeds possible?


Is that a thing?

I'm assuming that I can't just throw a 250k, or a 500k pot in there, and magic will just happen, right....?

and, yes! I am VERY serious about this inquiry.

Please & Thank You!
Best,
-M.A.


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PostPosted: Fri Oct 29, 2021 9:56 am 
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Fattyma4 wrote:
So.... what happened!? Does it work now?

I can answer this portion of your inquiry.

Because the OP was apparently struggling with a confusing/complicated problem, I contacted him by PM and offered to look at the pedal. (No, I don't do this for free, but my rates are EXTREMELY reasonable and I charge nothing except the return postage cost if I can't fix it!) I received the pedal by mail last week and found two problems when I inspected it:

  1. The kit had been sent with the wrong speed pot, a C10K instead of the specified C100K. So the speed control never saw the correct resistance interval across its span and wouldn't control the circuit properly. Fortunately, I had a C100K pot on hand to replace the erroneous one.
  2. During the course of the OP's efforts to get the speed control working, all three of the PCB solder eyelets for the pot were extensively damaged resulting in loss of contact with the circuit. This necessitated running wires between the pot legs and their respective connection points in the circuit, not a difficult fix once it's clear what the problem is.

These two repairs restored the pedal to full functionality and it's now back in the OP's hands.

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PostPosted: Fri Oct 29, 2021 10:58 am 
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duhvoodooman wrote:
Fattyma4 wrote:
So.... what happened!? Does it work now?

I can answer this portion of your inquiry.

Because the OP was apparently struggling with a confusing/complicated problem, I contacted him by PM and offered to look at the pedal. (No, I don't do this for free, but my rates are EXTREMELY reasonable and I charge nothing except the return postage cost if I can't fix it!) I received the pedal by mail last week and found two problems when I inspected it:

  1. The kit had been sent with the wrong speed pot, a C10K instead of the specified C100K. So the speed control never saw the correct resistance interval across its span and wouldn't control the circuit properly. Fortunately, I had a C100K pot on hand to replace the erroneous one.
  2. During the course of the OP's efforts to get the speed control working, all three of the PCB solder eyelets for the pot were extensively damaged resulting in loss of contact with the circuit. This necessitated running wires between the pot legs and their respective connection points in the circuit, not a difficult fix once it's clear what the problem is.

These two repairs restored the pedal to full functionality and it's now back in the OP's hands.


That's really weird since we took measurements specifically to determine that the speed resistance was indeed between 2k and 102k.

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PostPosted: Fri Oct 29, 2021 11:04 am 
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Fattyma4 wrote:
So.... what happened!? Does it work now?


Also, Hey Keith, What kind of Lunatic Mod can I play around/experiment with, to get the speed down to the gnarliest slowest, stupidest sssssssslowest speeds possible?


Is that a thing?

I'm assuming that I can't just throw a 250k, or a 500k pot in there, and magic will just happen, right....?

and, yes! I am VERY serious about this inquiry.

Please & Thank You!
Best,
-M.A.


No. Not the speed pot. You can't get much more range out of that. It will just cut out on you if you try.

Replace C13 - 18 with 1uF film capacitors.

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PostPosted: Fri Oct 29, 2021 11:04 am 
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byoc wrote:
duhvoodooman wrote:
Fattyma4 wrote:
So.... what happened!? Does it work now?

I can answer this portion of your inquiry.

Because the OP was apparently struggling with a confusing/complicated problem, I contacted him by PM and offered to look at the pedal. (No, I don't do this for free, but my rates are EXTREMELY reasonable and I charge nothing except the return postage cost if I can't fix it!) I received the pedal by mail last week and found two problems when I inspected it:

  1. The kit had been sent with the wrong speed pot, a C10K instead of the specified C100K. So the speed control never saw the correct resistance interval across its span and wouldn't control the circuit properly. Fortunately, I had a C100K pot on hand to replace the erroneous one.
  2. During the course of the OP's efforts to get the speed control working, all three of the PCB solder eyelets for the pot were extensively damaged resulting in loss of contact with the circuit. This necessitated running wires between the pot legs and their respective connection points in the circuit, not a difficult fix once it's clear what the problem is.

These two repairs restored the pedal to full functionality and it's now back in the OP's hands.


That's really weird since we took measurements specifically to determine that the speed resistance was indeed between 2k and 102k.

I think that the multimeter resistance measurement reported in THIS POST was erroneous, i.e. was 10.2K not 102K. A C10K is also consistent with the OP's reported result here: viewtopic.php?p=499455#p499455

And here's a photo of the pot when I removed it--clearly not a C100K:

Attachment:
C10K_pot-HarmTrem.jpg
C10K_pot-HarmTrem.jpg [ 47.19 KiB | Viewed 6871 times ]

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PostPosted: Thu Jul 21, 2022 11:49 am 
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Man, oh man....

I am very glad to hear that this eventually had gotten cleared up!
I believe that my over-interest in this whole jive turkey talk, was because I was going thru NOTHING similar, to that same issue, but I had just built mine, and wanted slower speeds, which I now have the answer for, with the Cap replacements Mod. Whomever it was with that switch & heat shrink, PLUS the sound sample, that's exactly what I'm considering an attempt at.

As soon as I read the first words of your reply, AFtER reading each and every back n forth, between the two of you, I knew EXACTLY what your response was going to be.

I swear, there are plenty of days that I would've spent , learning a heck of a lot more, just hanging around the forum, rather than most of my nonsense ideas, or hairbrained schemes I end up just getting distracted from, either way....

JUst wanted to offer my compliments to you, for handling yourself well, getting it figured out, and BONUS, there was also an additional Speed Cap Mod, when I finished up reading the final post in the thread! Three Cheers for you guys!

Thanks SO much for all of the assistance, throughout the years.

SO MANY MORE KITS TO BUILD, STILL!!!!

Cheers,
Best,
-M.A.


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