Casio PG-380 Midi Guitar
Several months ago Jason asked me if I could fix a MIDI Guitar. I’d didn’t have the slightest idea how to fix one, and only had speculative knowledge about how they work, so naturally I said “yeah, sure, piece of cake”. If I’d have known at the time the kind of gear lust this project would create I might have turned him down at the outset.
The Casio PG-380 is a guitar that translates the notes you pick on the strings into MIDI Notes. Think of it like a Keytar, only its ACTUALLY a guitar. You may think that the name brand somehow reduces the quality of this particular instrument, but you’d be mistaken; this baby is top of the line. It can translate amplitude, hammer-ons, and string bends with very little latency. I’d soon find out how hard to find, and how expensive, buying one of these would be.
The problem sounded simple: only the bottom two strings of the guitar were producing notes. At first I figured this must be a calibration issue or something, so I tweaked some of the pots on the board, messed with action height, etc in an effort to get the MIDI pick up to hear and translate the notes. This effort proved fruitless so I turned to the web.
How do you translate audio into midi? I had a vague idea how you could do this with envelope followers and some basic filter networks, but I wanted to understand how this thing actually worked before I could say with any certainty what was wrong with it. I looked around for a long time on the web and turned up nothing related to the technical aspects of converting the output of a guitar pickup to MIDI. In the end I relied on the premise that there must be a filter network to divide the audio by string, and a logic device to convert that analog value to a digital stream of bytes. Since 2 of the 6 strings were working, I could assume that the logic device was probably ok. I turned my attention to what I assumed was the filter network.
I cracked open the case and had a look around. I followed the traces from the pickup back to the 6 calibration pots to the series of capacitors that make up the filter network. I didn’t see anything visibly wrong so I returned to the internet to see if there were any already reported issues for the PG-380. Sure enough I came across this post, which identified a common problem as deteriorating electrolytic capacitors in the filter network. It turns out that electrolytic capacitors go ‘stale’ if left unpowered for a long stretch of time. So, just replace the caps, right? Almost.
I’m usually pretty reckless (or overconfident), especially with my own gear, but when it’s someone else’s very expensive stuff on the line I tend to be a little more cautious. I prefer to stick with old PCBS, with large thru hole components. Think of your grandpa’s large print books. This was a modern board with tiny surface mount components, something I’ve never dealt with before. I searched around for some techniques I could use to get these little caps off the board and settled on the “hot tweezer” method. This is essentially taking a blow torch to a pair of tweezers until they’re hot enough to melt solder, then gripping the cap and pulling it off the board. This worked for the most part, though there were some persistent ones that I ended up just jamming a soldering iron under an pulling off. That “technique” ended up being a little messy; there is a plastic separator under the caps that melted all over the place. Those tweezers came in handy for scraping that crap off.
As for the replacement caps, I went with the smallest long lead electrolytic capacitors I could find. I had some of these lying around already and ordered the balance from Mouser. Along with some other stuff for future projects (and posts). Replacement was easy. Cut the leads short, flux the pads, tin the soldering iron, and tack one lead in place. After tacking one lead solder the other post, then fully solder the tacked post. Just like thru hole only you’re tacking the caps on top of the board. It looks a little goofy, but not as goofy as playing a keytar…
Capacitors in place I plugged the guitar in and went to work. Whoa. I hadn’t imagined using a guitar to trigger a synthesizer would be so fun.
Here is a drone sound, with a completely unnecessary string bend at the end:
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Here are some chords, which I thought the pg-380 did a pretty decent job of sensing:
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And how about a silly FM bass chord:
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I’m addicted and I have to give this thing back at some point. Looking around on the internet, these puppies go for upwards of $1500. So, if you have a less than perfect PG-380 for sale, perhaps one that needs some new capacitors, I’ll take it off your hands.
I am experiencig the same problems with my PG 380. Because I want to sell it I need fix that problem. So could you tell me how much capacitors did cost you, and are they casio´s trade mark or I can use any other adequate. Maybe I am asking stupid questions but I am not very familiar with electronic components.
Thank you
I used plain jane aluminum electrolytic capacitors. Nichicon was the manufacturer, here were the mouser part numbers:
647-USR1H010MDD
647-USR1C100MDD
647-USR0J470MDD
Certainly not Casio’s trademark. You may not want to do this repair on your own if you’ve never done something like this. Maybe you’d be interested in selling the guitar to me broken
I ordered the above caps from Mouser, however when I pulled my board to change them i found 470 uf caps not 47 uf, which is part # 647-USR0J470MDD.
or does that mean 47.0? The replacement caps are much smaller than the ones labeled 470
You might take a picture of those and send it. I double-checked everything I have here and the ones I used were definitely 47 uF. It almost sounds like these have already been replaced on this guitar once…
This link should show you how the original board looked, and show you the values of the original caps. Those should be 47uF, not 470uF. And they ought to be quite small compared to replacement caps…
Boy i feel stupid..I pulled the wrong board. You’re right, 47 uf.
I’m going to try the repair tody.I’ll let you know how it goes.
It happens to the best of us Bob
At least you spotted the inconsistency before jumping in and unsoldering the wrong caps. I probably wouldn’t have spotted this until after I put it all back together…and it didn’t work.
Good luck with the repair, let us know how it goes.
@Grant Muller
The pg 380 is fixed. Great work. Thanks, Grant.
Total cost $7, $5 of which was shipping for the caps. Place in NJ said they would fix it for $275, so I saved a bundle.
Yep, shipping on parts always makes me cringe, the parts are $0.17 a piece tops, man I wish I had an electronics retailer nearby!
Good to hear that it worked out for you!
Hi Grant
I linked to your PG380 photo and article on my new Facebook group. Midi Guitars, Digital Guitars, Technology Guitars, Hybrid Guitars. There are always people on the Yahoo Midi Guitar Group looking for where to get there PG380 caps fixed and or how to fix theirs.
The caps are down on my PG380. So one of these weekends I will have to recap mine. My original caps lasted over 20 years. Thanks for the article.
Thanks Tim. I might have to join this Facebook group now that I have a new love for Midi Guitars
Good luck “recapping”, its not all that difficult, and you’ll easily get another 20 years out of the guitar (assuming MIDI isn’t overtaken by OSC…but I’ll have written a translator by then). Good luck!
Hi Mr. Muller
Reading your notes. Going by your part #’s It looks as though you only changed three. I have been reading up on this and I was thinking if was 6 to 10 cap. that needed to be changed out. I just bought a 380 off e-bay that was to be working fine they said, but when it got to me you could just hear the midi. All six string work but no power, the guitar part is fine.
Might you have interest in the repair of this guitar if I were to send it to you?
Thank You for your time.
Jerry from Michigan
Jerry, it is indeed 10 caps that need to be changed. It only looks like two in my article here because I make it look so easy
Just to make sure you’re dealing with the same problem, you said you could hear JUST the MIDI, does that mean when you plug the guitar into a keyboard or something, that you can play the keyboard? Are you saying that simply plugging in to an amplifier doesn’t work? I need to figure out exactly whats not working here before I take this on, the fix I define here fixes a problem with MIDI only, so if you’re MIDI out is working, doing the steps in this article won’t work…
I have one of these guitars also, I did the capacitor replacement but it seems like im getting noise from the synth volume pot, how would you try fixing that. the synth is working its just covered up by rediculous static
You might just have a bad pot, you can probably just do a one to one replacement on that guy. I’ve never looked at this but as long as it’s not a digital pot and it’s just some 100K analog pot you should be fine. When I’m back at the shop I’ll take a look and see what it is, but if you can replace the caps, you definitely have the skills to replace one of these.
I received PG380 guitar that is very good condition and mostly being in storage not played.
I do not have any additional sound card but would like to purchase card with usefull sounds for guitar player ( nylon string, bouzukki, balalika accordeon etc.
Does anyone know where I can find RaM Rom cards?
Since bass strings does not respond to trigger I believe I have to change capacitors. Is that job that any electronic person can do or I have to have a specialist. I brought guitar in Guitar store and technician is scared to touch it.
Please advise
As for where to find the RAM cards, I have no idea, the one that I was working with didn’t have one either. You might just do some general searching on the internet or eBay or something.
I’m not surprised the guitar technician didn’t want to touch it, it’s a very unusual problem to repair. Their focus is really the mechanics of the guitar. If you follow the instructions, you should be able to handle this on on your own if you’ve ever soldered anything…I’ve been offering to fix these if people want to pay to ship them to me, just send me an email through my contact page and I can try to work something out with you if you want.
Hi folks.
I have done about 6 of these now with another one due in my workshop in the next few days. Several things about surface mount caps. First is sniff! If it smells like the tom cat has been in there then the best thing to do is to start with the main power decouplers and work out to those in the pickup filters. This will pay dividends even if all the notes are working as the response time improves with these changes made.
Dont twiddle! Leave the presets alone until you have swapped out the caps. Pay attention to those that look deformed or misshapen as these should be replaced wherever they live.
I use miniature electrolytics as Grant says although I did see one that had tants. I avoid surface mount in this particular unit as there is space for the better and more long lasting caps in there. The batteries and its compartment are typical of the period and are now rather long in the tooth! I offer a double stabilised power supply plugged in via a mini xlr connector in place of the standard DC power plug and cut out the batteries completely. You only get a couple of hours from them anyway so they really are not worth the trouble. I have also had interesting results with driving an external synth module of the same era namely the Yamaha FB01 which is a very early FM unit with I think 4 operators. Using one of these set to a brass setting you get the most fantastic raw brass section sounds. For a guitar synth of this vintage there is still a lot of life left in them and it is really only relatively recently that better units have come onto the market. If you want more or different sounds get yourself a small stage mixer and either a modern small synth (Yamaha PSR350 that the schools use to teach with would be fine) and mix everything together.
Happy twiddling!
Regards
Dave Tutt
Thanks Dave for the tips. Tants are tantalum capacitors for those who aren’t familiar with the shorthand. Good idea with the power supply modification, I hadn’t thought about doing much other than making it play properly again.
I used to play one of those little FB01 models actually, definitely a fun desktop synth module, but for modern players I would recommend just getting a small USB->MIDI interface for your laptop and triggering any number of softsynths from your there.