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Author Topic: debugging a pre-refine pcb  (Read 197 times)

Offline JJMT

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debugging a pre-refine pcb
« on: February 17, 2019, 12:34:30 PM »
Hi Everyone! I thought I would thank everyone for all the help. I’ve read a lot of posts in this forum, and it has helped me out a lot. I just did a PTP conversion on my pre-refine (‘96) Fly Classic. But there was a pretty big bump in that road (it didn’t work ;)), so I thought I would give back a bit and share my experience.

As indicated above, my Fly just got a major make-over. I removed the tape connectors and wired PTP. I replaced the pickups with Rev 2 Dimarzios, replaced the pots (Bourns series 95 on the mags, series 82 on the piezo), replaced the switches with Electroswitch toggles, and replaced the jack with Switchcraft. I also modded out the master volume, used separate volume and tone pots for the piezo, and removed the mono/stereo switch. I also got rid of the tapped center position and replaced it with both pickups in parallel. So, when I put it all back together and it didn’t work, there was a lot to debug. It took all my free time over about two weeks to reach the conclusion that the problem was actually with the pcb. With none being available for sale, I needed to debug and fix the board. I thought I would start a thread for how people repair their boards, given that this is going to continue to be a problem for everyone.

My symptoms: (1) piezo did not work at all – no sound; (2) mags worked, but the volume was very low; (3) interestingly, the mag output was independent of the mag/piezo selector switch – even when set to piezo only there was a little output from the mags; and (4) I had about 5v dc on the tip of the jack. I decided to pull everything back out of the guitar and trace the signal. But my tone generator died a couple years back, and I was unexcited about getting out my scope, as I would have had to clean my bench to make room. So, I took a simpler route.

Tools used:
1. Android phone with the app Function Generator installed.
2. A homemade cable: stereo 1/8 in jack (plugs into phone) and a couple of wires (tip and ground).
3. Multimeter: Fluke 112, used to test AC and DC voltages, signal frequency, resistance and capacitance.

What I did:
With the pcb still in the guitar, I checked the piezo for signal (to make sure it was still working). Using the multimeter’s AV voltage reading, I verified that I had a signal when I strummed the guitar (0 when not strumming, non-zero when strumming). I think I got about 300 mv with a good strum, which actually seemed like kind of a lot. But I could be remembering that value wrong.

With the pcb out of the guitar, but with all the pots connected (I just pulled everything out of the guitar at once), I soldered my home made cable to the piezo input and ground. With the phone I sent in a signal (I randomly selected 220hz) at about 300mv. Oh, I also soldered the battery connectors to the battery and ground connectors, just as would have been in the guitar, and connected the battery. The LED flashed, and I was good to go.

To trace the signal, I used the multimeter and the schematic found here:

http://jmstaehli.com/images/guitars/Parker Fly Schematic.pdf

I simply checked for AC volts as I moved from component to component, and checked the frequency to ensure that what I was seeing was my signal (220hz). My signal disappeared after C1. I checked the capacitance of that cap and go about 1.75 uf, resistance of a few megaohms, and there was continuity from the previous component (R3) and to the next one (C2), so I felt like the cap was OK (although I had no idea what value it is supposed to be). I started looking around.

Because of the odd behavior of the mags and the lack of piezo function, my attention was drawn to Q5 and Q1, which is where the two signals meet. Not really recognizing a problem there, I kept following the connections until I got to the MC33179P. That was supposed to have Vcc one one side, and Vee on the other side (per the schematic). But that was not the case. Rather than seeing Vee (-9v), I got something less that 1v. At that point I was ready to replace the IC. But someone here had mentioned that the two most likely things to fail on the pcb were that IC and the LTC1044. That IC seemed to be working correctly, flipping the 9v into -9v. But I noticed that the -9v didn’t make it to the MC33179P. In fact, Q7 had -9v coming off one leg but less than 1v coming off the other. I started planning to replace Q7, and the MC33179P (just to be sure).

A visual inspection under magnification did not reveal any cracks or anything. I gave Q7 a push with my finger and wiggled it (my finger) a bit. The voltage on the IC immediately went to the right level, and I all of a sudden had signal all the way to the output. Bad solder joint on one leg of Q7. I re-flowed it and added a touch of new solder. Good as new. Oh, and the 5v dc I was getting at the output disappeared. Not sure why.

I still had to check the mag side of the board, so I de-soldered my input from the piezo and soldered it to the mag volume pot input. I quickly verified that I had basically the same signal coming out of the board as I had going in. So I didn’t touch anything else. I put everything back in the guitar.

Probably the solder joint had been strained when I removed the tape connectors from the board, but I really don’t know what happened. The guitar sounds better than it ever did. :) I though I would post just to let everyone know that having your pcb "die" in your pre-refine need not be the end of the world.

Re: debugging a pre-refine pcb

Offline Patzag

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Re: debugging a pre-refine pcb
« Reply #1 on: February 19, 2019, 01:40:22 PM »
Cool story.  I had to read the whole thing to realize that you had handled it successfully.  Well done!

Some photos would be nice!
Teal Fly Classic 1998 / White Deluxe Hard Tail 1994 /Axe FX II

Re: debugging a pre-refine pcb

Offline JJMT

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Re: debugging a pre-refine pcb
« Reply #2 on: February 19, 2019, 09:07:37 PM »
Cool story.  I had to read the whole thing to realize that you had handled it successfully.  Well done!

Some photos would be nice!

LOL. Yeah, I was wondering whether anyone would have the patience to read the whole post. It was one of those things where I just had to tell *someone*. ;) Not many people in this world would care....

I'm in the DC area and it looks like we're going to have a snow day tomorrow, so I'll see what I can do about pics. What I can say now is that I've owned this guitar for 22 years, and I've never liked it more than I do right now. I guess it's good to have some sweat equity in it.

Re: debugging a pre-refine pcb

Offline Patzag

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Re: debugging a pre-refine pcb
« Reply #3 on: February 20, 2019, 06:51:16 AM »
That's cool.  And yes, pictures would complete the story and give others a chance to see what the conversion looks like.

Oh ... welcome to the forum!
Teal Fly Classic 1998 / White Deluxe Hard Tail 1994 /Axe FX II

Re: debugging a pre-refine pcb

Offline JJMT

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Re: debugging a pre-refine pcb
« Reply #4 on: February 20, 2019, 08:50:26 AM »
OK. Let's start with the finished product, shall we?

https://ibb.co/TY6Ybk7

From my perspective, the improvement in functionality with the new pots and the new knobs is huge. The Fly is a guitar that encourages you to play with the knobs all the time, and I never liked the originals much. The Bourns knobs have a better feel (subjective), and the Ernie Ball tele knobs feel nice in the fingers and don't screw up the aesthetics too much. The switches look good and feel better to me (again, subjective).

The guts are here:

https://ibb.co/0CR45Cj

The solder work is a bit messier now that my first time through (with virgin parts). Sigh. The whole project started when I decided that I wanted to improve the shielding to get rid of a minor RF hum issue. I should have used paint, but I didn't have enough, so I went with the foil tape (which I had a lot of). I did use paint on the pickup cavities. It was during that process that I tore a tape and everything reeled out of control after that. Well, it all turned out OK. The guitar is dead silent now, even when not touching anything.

Finally, the jack is here:

https://ibb.co/6yBZfjq

I still have that hole to fill. I couldn't find a plug locally, and Amazon has not yet delivered. Honestly, even the hole is better. I found myself obsessively checking the stereo switch all the time. It just wasn't healthy. :P

Re: debugging a pre-refine pcb

Offline jb63

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Re: debugging a pre-refine pcb
« Reply #5 on: February 20, 2019, 09:58:33 AM »
This is really great! I may have to do that to mine when it starts to buzz.

Probably the inappropriate place to ask, but I could really use that red button stereo switch if you are done with it! Its one of about 4 parts I've been searching out for about 3 years!

Re: debugging a pre-refine pcb

Offline JJMT

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Re: debugging a pre-refine pcb
« Reply #6 on: February 20, 2019, 10:07:16 AM »
could really use that red button stereo switch if you are done with it!

PM me, or whatever this forum allows....

Re: debugging a pre-refine pcb

Offline Big Swifty

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Re: debugging a pre-refine pcb
« Reply #7 on: February 20, 2019, 03:13:36 PM »
Nice work, and a lot of it too!

(De-bugging....what a pleasurable pastime it is... :-) )

Glad you got it all going again, Parker on!!

B.S.
94 Fly Deluxe
2010 DF 524
The system can't get you in your dreams.

Re: debugging a pre-refine pcb

Offline Patzag

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Re: debugging a pre-refine pcb
« Reply #8 on: February 20, 2019, 04:57:48 PM »
Wow. Nice and neat job there.  Very pro.
Well done!
Teal Fly Classic 1998 / White Deluxe Hard Tail 1994 /Axe FX II