Tips / Resources for repair on micro boards

[effectsbay]

I may not be asking this right.. so I'll describe what I'm talking about.

I have a T-Rex Tap Tempo Delay pedal that stopped working after a One Spot daisy chain plug touched the enclosure. The pedal still passes signal (on or off) but no effect. No delay, etc. is happening. I thought it might be a fun challenge to get this thing working, but when I cracked it open, it's a board filled with the super tiny components.

Are there any resources for working on these? Special tools? Special tips for the iron? I have a feeling one or both of the ICs might have got fried, and I want to be sure I go about things the right way before getting over my head.

Any advice is greatly appreciated!
Thanks!
hank

[mth5044]

Can you tell if it's based on a common chip set (or more likely) a programmed/computer based circuit? There might be some kind of circuit protection in there that fried you could fix, but is likely that if a chip is gone, you're in trouble.

The tiny components are called SMD or SMT, and there are quite a few posts on this board and a lot of YouTube videos about proper equipment and procedures. I don't know them off the top of my head, but it's been discussed quite a bit.

[effectsbay]

Can you tell if it's based on a common chip set (or more likely) a programmed/computer based circuit? There might be some kind of circuit protection in there that fried you could fix, but is likely that if a chip is gone, you're in trouble.

The tiny components are called SMD or SMT, and there are quite a few posts on this board and a lot of YouTube videos about proper equipment and procedures. I don't know them off the top of my head, but it's been discussed quite a bit.

Thanks. There are 2 ICs on there. Tiny. There is some writing.. and all I can make out is the following:

0820
Z952

Thanks! I'll do a little digging on SMD/SMT
hank

[R.G.]

I have a T-Rex Tap Tempo Delay pedal that stopped working after a One Spot daisy chain plug touched the enclosure. The pedal still passes signal (on or off) but no effect. No delay, etc. is happening [...] I have a feeling one or both of the ICs might have got fried,

What you describe is a fairly standard way to kill a linear regulator that's poorly designed. I don't know the circuit you're describing, but the description of what happened is very familiar. I've posted warnings about this chain of events here in the past.

Linear regulators in general, and also the highly-integrated single chip switching regulators are good at only letting through the right amount of current in the intended direction. There is generally a big, fat capacitor on the output side. If the INPUT side is suddenly held at zero, like by touching the + side to a grounded metal enclosure, that big fat capacitor on the output is discharged through the regulator backwards. The sudden high current kills the regulator.

Every regulator application note I've ever seen shows a diode connected from the output to the input so if the input is shorted to ground, the output cap is harmlessly discharged through the diode. Unfortunately, many "designers" neglect this, as the circuit works OK without it - at least until what you describe happens. When you get the daisy-chain short, the regulator becomes a Darkness Emitting Diode (DED    ) instantly. This may or may not let the chips the regulator was regulating for die when power is next applied.

I ran into this in my day job with TrueTone (formerly Visual Sound). In my once-day-job of power supply designer, I got familiar with what users say when equipment dies - "The power supply killed it!!"  We got some complaints about the 1Spot killing pedals, and I investigated. That turned up the chain of events I just typed. I tried, but I could not think of any way to make the 1Spot make up for the pedal maker leaving off the protection diode inside their pedal. Some things just can't be guarded against.

But we did start offering daisy-chain condoms. These are just little plastic covers that slip over the un-used daisy-chain ports so the exposed positive side (thank you, Boss!) can't touch exposed grounded metal and cause the issue.

I thought it might be a fun challenge to get this thing working, but when I cracked it open, it's a board filled with the super tiny components.

Are there any resources for working on these? Special tools? Special tips for the iron? I have a feeling one or both of the ICs might have got fried, and I want to be sure I go about things the right way before getting over my head.

I do a lot of SMD work these days. First and foremost, you need magnification. If you can't see it, you can't work on it.

I've posted it before, but look for a cheap pair of stereo magnifiers on a head band. I don't know where you live, but here in the USA, we have Harbor Freight and they sell headset magnifiers for aobut $5-10 depending on what sale is happening at the moment. I must have six sets of these. What really makes SMD work easy is a good stereo microscope. I found a used B&L stereo zoom surplus, and its the Right Tool, but they're quite expensive unless you get lucky like I did.

After magnification, you need a fine, pointy soldering iron tip, generally in a lower wattage than for non-SMD; or at least temperature controlled.  You can use ordinary solder, but super-fine, small-diameter solder is much better. It's easy to get too much solder on these.

Sharpened chopsticks are much better for positioning parts than hands. Tweezers, maybe. I like chopsticks used one at a time to slide parts into place.

Liquid soldering flux. A small bottle will last forever.

Q-tips for applying flux.

In your case you're going to need a way to get chips OFF the board. I like soldering tweezers (MCM electronics) with two heated sides to melt all the pins of a DIP IC at once. Quad packages - no good manual way other than either Chip-Qwik, stainless steel shim stock or clipping off leads and tossing the now-leadless package.

And patience. Lots of patience.

[effectsbay]

R.G. that post was amazing. I'll start with the tools and come back to this circuit. My solder is too thick for sure. I think I have a tip on my lower wattage iron that can handle this level of work.

Thanks so much!
hank