Man, talk about the project you don't want to make a mistake on. I finally got my pots in, and was ready to wire this thing up. After connecting all the footswitch boards and jacks, I connected it to the AC power supply I bought, and...nothing. I probed around, and noticed that nothing was happening at IC1. So I checked the test voltage pads, and they were way off. So hack to the build doc I go, and I noticed that I put the regulators in upside down (heat sinks toward the PCB). I flipped them, but burnt a pad off REG1 (the 7815 positive power supply). I can see that the power test pad has -15V where it should, but REG1 isn't making the connection now and the positive test pad is around -11V. So I have a series of questions.
- What are the chances that I've fried all the components and/or the board? Should I just give up here and start over? What's the effect of putting the wrong voltages through ICs?
- There's a big electronic supply store in Kansas City, and they have some 7815's in stock, but I can't seem to find a data sheet on them. They're 7815JP6 from Jim-Pac. Has anyone had any experiences with them? http://www.eskc.com/product-p/sr_7815tjp6.htm (http://www.eskc.com/product-p/sr_7815tjp6.htm)
- When I burn out pads, I normally use some thin trace wire and put that on top of the board. However, this pad connects to a series of components, making that more difficult. I scraped down to the trace, and think I can connect the component's lead into the 2 traces coming out of the pad (It's the V0 pad on REG1 if you look at the schematic), but I wanted to know if anyone has any helpful tips when doing this
Thanks for the help! I'm hoping that it's salvagable, but I'm also preparing for the worst (from both time and expense).
I would bet that it is still manageable to rescue the board. I'm not sure about the ICs, but I would start with getting the voltage regulator operational.
Which pad of the regulator did you burn? Only one side or both? depending on that, you could probably wire that leg of the regulator to the next component it connects to and/or use some jumpers to fix the rest. once you get the correct voltage there, I would check the functionality of the board and if it doesn't work replace one IC after the other. I hope you used sockets...
Quote from: m-Kresol on January 22, 2017, 06:52:51 PM
I would bet that it is still manageable to rescue the board. I'm not sure about the ICs, but I would start with getting the voltage regulator operational.
Which pad of the regulator did you burn? Only one side or both? depending on that, you could probably wire that leg of the regulator to the next component it connects to and/or use some jumpers to fix the rest. once you get the correct voltage there, I would check the functionality of the board and if it doesn't work replace one IC after the other. I hope you used sockets...
That goodness for sockets. That board has 13 ICs and transistors. As far as the pads, 2 of them are rough for wear but should still be usable. One is totally gone, but the trace that runs through it goes to 4 different components. I think I can scrape the mask off, the run some jumper wire across the trace and connect it.
Quote from: Timko on January 22, 2017, 08:33:56 PM
Quote from: m-Kresol on January 22, 2017, 06:52:51 PM
I would bet that it is still manageable to rescue the board. I'm not sure about the ICs, but I would start with getting the voltage regulator operational.
Which pad of the regulator did you burn? Only one side or both? depending on that, you could probably wire that leg of the regulator to the next component it connects to and/or use some jumpers to fix the rest. once you get the correct voltage there, I would check the functionality of the board and if it doesn't work replace one IC after the other. I hope you used sockets...
That goodness for sockets. That board has 13 ICs and transistors. As far as the pads, 2 of them are rough for wear but should still be usable. One is totally gone, but the trace that runs through it goes to 4 different components. I think I can scrape the mask off, the run some jumper wire across the trace and connect it.
it's a double sided board, so you have traces on the front and back and some traces might connect to the other parts from other component's pads. So which pad is it? centre, left, right?
depending on which it is, check the datasheet to see if it's the GND, in or out connection. once you've got that figured out, check the schematic and have a look where that pad is supposed to be linked to. Take your multimeter and see if those connections are maybe still there (eg from the pad on the other side of the board?) and check if some of the components that it's supposed to be connected to are maybe still connected to each other. hope that makes sense...
if they are connected it could be as easy as running one wire, if not multiples. your method of scratching the solder mask off and soldering to the trace might work, but is hard too.
Ok, here are the pictures.
This is where on the PCB the pad is burnt:
(http://i.imgur.com/5mcgJef.png)
Which corresponds to this location on the circuit schematic:
(http://i.imgur.com/3k3iQXr.png)
Now, I am fortunate in that all of the trace coming out of that pad is on the back of the board. I've marked the pad, as well as the part of the trace I scraped off as well as the parts of the trace that aren't scraped off that need to connect to the components on the board:
(http://i.imgur.com/3bp8Fhv.jpg)
I think this is going to be very doable! Did you check for continuity between C57 and RX3? If they are connected you can either solder the leg of the 7815 to the opened trace or to one of the pads you labelled. if they aren't connected you need to connect those two areas of components too (d10/c57 and rx3/c59)
It doesn't look like you would have had reverse voltage or overvoltage on either of the rails - just no voltage or not enough - so there is a chance that other components down the line are OK. I'd say that as long as you get continuity between all the traces that may have burnt (using jumpers as necessary) then you should be OK. But what I'd do is remove all the ICs from their sockets before plugging it in again. Make sure you get +15 / 0 / -15 at the test pads before putting them back.
Quote from: aion on January 23, 2017, 06:22:18 PM
It doesn't look like you would have had reverse voltage or overvoltage on either of the rails - just no voltage or not enough - so there is a chance that other components down the line are OK. I'd say that as long as you get continuity between all the traces that may have burnt (using jumpers as necessary) then you should be OK. But what I'd do is remove all the ICs from their sockets before plugging it in again. Make sure you get +15 / 0 / -15 at the test pads before putting them back.
Agreed. All of the components are coming off the board prior to me starting again.
One other question. Can I use an LM in place of the MC regulator? Looking at the datasheets of the 7915 parts they look really, really close. The only difference seems to be the MC7915 can handle more voltage. If not, no worries. Someone in the PIF offered me a couple of the LM line, which would be nice because it doesn't require a Mouser order.
In the schematic there is a LM 7915 so I guess that will be no problem.
Yeah, they'll perform identically. I put a MC in the parts list just because it has slightly better specs but it won't make any difference here.
I got a couple of new regulators in the mail today, so I put this back together. The thin trace wire I have worked perfectly over the trace on the board I soldered on top of. The good. Eww is that the pedal has sound now and everything seems to work. I still need to go through each IC and make sure they're functioning as they should, but this board will survive!
Thanks to tcpoint for regulators hook up!
Here's the solder bridge I built. It turned out pretty clean.
(http://i.imgur.com/WmsUsk4.jpg)
Fwiw, a good reference for this kind of thing, or even general assembly is IPC-A-610. It helps manufacturers determine appropriate workmanship standards. You can download redlined copies in PDF, right from IPC. (Or download a bootleg copy if you search. No judgement.) We used to live and breathe it in my past life.
Many of the highest standards are way overkill for pedals, but you can still learn a lot by paging through it, and get some ideas of what to do in the event of a problem like this. At the least, it may provide some reassurance that a mistake can be repaired.
I figure few people here know this exists, and I hope it helps someone.
Mostly, I'm glad you were able to get this awesome pcb working again!