CMATMOD Brownie (BSIAB II) Low Volume

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Still reading 001 after green wired removed from circuit board.

Still reading 001 after C1 cap removed. I tested C1 with meter at 200 and got 1...the meter simply doesn't change.

Interesting indeed. Possible another component is faulty as well? Also, for future builds, is it good practice to set the meter to 200 and test each component before soldering it in? Are there components that this method wouldn't work for?

Meanwhile, I've sent my Brownie to Chad at CMATMODS for repair. I did ask him if possible if he could tell me what's wrong with the circuit after fixing/replacing it. I'll have enough on my plate with the BSIAB II and if I have a functioning version of it it'll probably be easier not to get burned out on it. In a sense I'm actually quite enjoying the learning process here and I feel I'm having more fun learning these things than I would be having using the pedal.

Or at least, the same amount of fun.

Ironic, I know

[Slowpoke101]

Odd result. OK on sending the other pedal off for repair. Sometimes it is necessary.

C1 is most likely OK. Testing parts prior to assembly is a good idea but usually parts are fairly reliable. But testing resistors to make sure that you have the correct value is a very good thing to do. Sometimes the colour (color) bands are difficult to see and some can be marked wrong.

Now, where C1 was soldered to the board, set your meter to the 200 range and measure across the two solder pads.
Your meter should show 1.

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Just measured. Across the two pads where C1 was, I am getting 1. I still need to work on neat component removal. I had to use pliers to pull the legs out after sucking as much solder out as I could. I do remember it going in quite tight. I tried to be careful as pulling on parts like that seems it could pull the pads out with it.

I assumed it would come out easily if I removed all the solder. Perhaps I wasn't as thorough as I thought. I could see plenty of light shining through the pads. Just want to make sure my technique is good so I don't damage the PCB by removing other components.

[Slowpoke101]

Removing soldered components can be difficult. It is no always possible to remove all the solder prior to removal of the component. With components with two leads (more leads make this more difficult), heat one solder joint while applying a SMALL amount of lifting force onto the leg being heated, melting the solder and pulling the lead free from the board. Clean up the solder still in the hole with your solder sucker. See if you can find Solder Wick ( De-solder Wick, Solder Wik ). It's a flux coated braided copper flat wire which when placed onto a solder joint and a soldering iron is applied to the braid, heating both the braid and the joint, the solder flows (wicks) into the braid and away from the joint. Careful control of both heat and time are needed to avoid board damage due to excessive heat but the Wick is very effective.

Re-install C1 and redo the last resistance test. The meter should read 1. If it does, resolder the green input wire back to board connection point I
With the pedal in Engaged mode (not Bypassed), with no leads connected to the pedal's input and output sockets, your meter still set to 200, measure across C1 again. The meter should display 1.
If it does display 1. Apply power to the pedal, set your meter to the 20 DC range and measure the voltages on Q1.
Let us know what you find.

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Will get this done ASAP. Broke the leg of the cap trying to put it back in; must've fatigued it with the pliers during removal.

How can you tell if the board is damaged from excessive heat? There was one or two times on the board I think I was holding the iron lazily and it wasn't heating the pad so well, and I could've had the iron on one spot for as long as 10 seconds without the solder melting.

I'll need to buy another cap to replace that one. 250pF ceramic cap...I'll remember that. Might as well got some solder wick while I'm at it.

[Slowpoke101]

That is disappointing. The small ceramic disc capacitors can be a bit fragile and it is easy to break the legs off them. If you have to bend their legs, you try not to bend the legs right at the body of the capacitor. Leave distance of about 2mm (3/32") from the body before bending. That way you don't stress the leg bonding to the capacitor. Not to worry.

When you get some de-solder wick, find a junked electronic item (old stereo, radio, whatever you find) and practice de-soldering. It will not take too long to get the hang of it. I forgot to mention that as you use the wick it will become loaded with the solder that it has "wicked" up. You cut of the loaded (used) section and dispose of it sensibly. I generally de-solder a few solder joints then cut off the used section. If you leave the used section attached it will act as a heatsink, slowing the melting of the solder you want to remove.

Damaging a board through overheating. It is easy to do but boards are fairly tough. You will smell it as it starts to happen. The smell is unmistakable. Visually the board will start to discolour and may bubble up (fibreglass boards). Phenolic boards (brown colour) don't smell too bad when overheated but the copper traces and component pads de-laminate off the board.

Holding the iron to a pad for over 10 seconds is excessive. Fortunately your iron had poor heat conduction at the time so no harm should of been done.

Believe it or not you don't actually need the capacitor C1 to be installed for the next test. C1 is mainly used as an RF choke point, that is it helps keep the pedal from picking up radio stations or other sources of RF (radio frequency). You can perform the next step without C1 being installed.

Set you meter to the 200 range resistance test. Measure across the two solder pads where C1 would be installed. If the meter displays 1, then go to the next step.
Resolder the green input wire back to board connection point I. With the pedal in Engaged mode (not Bypassed), with no leads connected to the pedal's input and output sockets, your meter still set to 200, measure across C1's solder pads again. The meter should display 1.
If it does display 1. Apply power to the pedal, set your meter to the 20 DC range and measure the voltages on Q1.
Let us know what you find.

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Just did the test. Everything cleared.

On Q1 I get:

Gate: 0.99
Source: 0.99
Drain: 5.28

[Slowpoke101]

Looking good.
OK, next test.
Meter set to 200 range resistance check again, no power applied and no output lead connected.
Pedal set to engaged mode and no input lead connected.
Measure across the input connector - yellow wire and black wire. Your meter should show 1 (no short circuits).
If this is right the on to the next step.
Connect an input lead with nothing connected to the other end (not plugged into your guitar) and retest across the input connector. Your meter should show 1. If it shows other than 1 - say 000, the input socket is shorting somewhere, usually to the pot body under it.
Let us know what you find.

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So test the lugs of the input jack, right? If that's correct, I did that and got 1. Seemingly it checks out.

It also read 1 while a jack was plugged into the input jack. Same reading: 1.

[Slowpoke101]

This is looking very good. Now for the next bit that will make you think that I have lost my mind.
Look at Q1. Notice that the flat face of its body faces towards the centre of the board.
Take Q1 out (unplug it from the socket) and rotate it so that the flat face is now facing the outer edge of the board (plug it back into the socket).
Connect your guitar and amp. Apply power and test your pedal.
If it still isn't working correctly, measure the transistor voltages again and let us know.
Good luck.

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With the transistor reversed, it still doesn't work, but with the knobs all the way up I do get at least some signal. About 5% as loud as my clean volume but still something. For a while it was not having any sound at all. However, the lack of drive/distortion was still there. I only mean that there was guitar signal going through and coming out, instead of complete silence, but the original problem remained the same.

After being on for about 2 minutes, though, all the sound went out, and was replaced by a loud static/crackling sound that only goes away when I switch the pedal off.

Now it reads, with Q1 reversed:

Q1:

Gate: 6.14
Source: 0.65
Drain: 0.00

Q2:

Gate: 6.22
Source: 6.22
Drain: 8.55

Q3:

Gate: 1.95-2.21*
Source: .9-1.3*
Drain: 1.2-1.4*

Q4:

Gate: 1.86-2.31*
Source: 1.25-1.41*
Drain: 8.57

Q5:

Gate: 0.06
Source: 1.09
Drain: 3.55

The * numbers simply indicate the meter looked very unstable when testing these. All the other numbers got a solid, static result...when I tested these, the meter seemed to jump very quickly between higher and lower values in the indicated range, and wouldn't settle on a single voltage reading.

[Slowpoke101]

OK. The reversal of Q1 answered my concern that you may have had a transistor that had its Drain and Gate transposed. It happens a lot these days.
Put Q1 back into the normal position and try the pedal again.

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Does that mean that on a lot of transistors made today the Drain and Gate legs are reversed?

I put Q1 back in the normal position and tried again...nothing but static/crackling that seems to get louder and louder over time. No signal. Measuring Q1 normally oriented:

Gate: 0.84
Source: 0.84
Drain: 5.26

If the pedal worked with Q1 reversed, would that indicate that the Drain and Gate legs were reversed? Do the measurements indicate that they're properly oriented since the Drain read 0.00?

[Slowpoke101]

Part of the problem with TO-92 packaged FETs (Field Effect Transistors) is that the most common units that are used in effects pedals are no longer manufactured in large volumes and they are getting hard to obtain. So some units may be low specification devices - they work but may not work as well as you would expect. Some manufacturers did use different pinouts for the same series - because someone ordered them that way or it was a manufacturing error. Most suppliers do try to supply the pedal builder fraternity with good FETs but sometimes bad or not so good units make it through. Ebay can be a nightmare to buy these types of FETs through. I gave up a few years ago.

It can be a bit of a effort to sort through what is currently available. But there are ways to sort the gold from the dross.

Now it reads, with Q1 reversed:

Q1:

Gate: 6.14
Source: 0.65
Drain: 0.00

If the gate was actually the drain and the drain was the gate, the measurements would be good. But the pedal sort of worked like this. Pity Q2, 3 and 4 voltages where very odd. So we shall now attempt to lay the pin orientation problem to rest now.

Set your meter to the 2000 resistance test range. Place a transistor (let's call them FETs) on a non conductive surface, flat side up and the legs facing towards you. Place the meter's red lead to the centre pin and the black lead one of the outer legs. If the black lead is connected to the drain the meter will read anywhere between 150 to 650. If the black lead is connected to the gate the meter will show 1. Now move the black lead to the other outer leg and see what the meter displays.

Between the source and the drain the meter will show anywhere between 150 to 650. Between the gate and the source the meter should show 1. You have now identified the gate leg and which legs are source and drain. Now you may be wanting to identify which leg is actually source and which one is drain. There is no simple test for this and with these types of FETs you don't need to know. Why? Because with these types of FETS the drain and the source are transposable. It doesn't matter which way they are connected. Please note that this test only applies to this sort of FET.

If you are interested, place the black lead on the centre leg and then place the red lead onto the gate. The meter will now read around 1000. The device is a sort of diode so gate polarity does matter.

Check all the FETs out and see if you have any that are different. If you do, plug those back in to the BSIAB2 in the opposite direction. You can't hurt them in a low voltage unit even when incorrectly connected. But there is one thing that I think that you have noticed and that is once the unit has been running for a while (but still not working correctly) the unit will start to fail badly and to get it to work again, you have to unplug it and let it cool down. That is actually what you are doing - letting it cool down. Depending on the amount of current flowing in the FET junction (when incorrectly installed), the junction will heat up and stop working. There usually is no damage from this but it can happen, so be aware of this.

See what you find and good luck.