Guitar Repairs

guitars

      Some basics to get out of the way first. There are lots of guitar makers, lots of different types of construction and lots of different needs of a guitar. In all cases though the primary issues boil down to the same two major points that define a guitar and govern its construction. It takes a couple of days to get a guitar sound box glued together. It takes about a week to get the fingerboard, nut and bridge set up. When you buy a guitar, whether it is an electric or and acoustic, you are buying a neck and fingerboard first, and a body second. It is the neck you want to pay attention to up front when you buy it, and later as it ages. The sound box or body can be considered a passive component. It is the neck and strings you will be laying hands on and this will define the playing experience as good or bad.

Stewart MacDonald is a great resource for tools and tips.
http://www. stewmac.com

Things to look for and the order to look for them.

   — 1. Is the neck straight?

      This check is done with the strings loose (or off), good lighting and an 18" strait edge to check for bow, and a shorter strait edge to check for high or low, (rocking) frets. You should be able to hold the butt of the guitar to your nose and look towards the peg head, down the length of the neck like a railroad track. it should not twist down the face from one corner to the other, or bow up, down, or in any direction when viewed down the side of the fingerboard. It should look as flat as a mirror any way you can look at it. If it is a new guitar it may bow or twist later, so know your brand and trust your gut. A good build feels different than an unfortunate assembly.

Neck Bowed or Strait pix

      This check should also be done every time the strings are changed as that is when you can make adjustments. Bowing of the neck is controlled by the truss rod vs. string tension (ignore heat and humidity as not relevant cause' you can't do anything about it). It is hard to get to the truss with strings on. With the strings loose or off the guitar, there should be no bow in the neck at all. After a set of strings is strung, and tuned up, there will be, and the resulting bow will be appropriate for whatever gauge the string set is. Use the short strait edge to examine any frets that might stand out like bad teeth from the rest of the set. Press down on the ends of a few frets and look for any that spring back out of the finger board (loose ends). They can be set again with super-glue, (don't make a mess).

   — 2. Does the string radius match the radius of the fingerboard?

      Some guitar fingerboards are almost flat. Folk Guitars and some electrics. Whatever the radius (or not) of the fingering board, that radius should be reflected in the bottom side of the string set. The top side will take all the differential of the string thickness increase from thin to thick strings. If you plan to do a lot of finger slide playing, you may want to flatten your radius or find a bottleneck style slide that closely matches the radius of the top side of your setup. Any changes you choose to make in the radius will need to be done by tooling the nut and/or bridge, in harmony with the next step, using thin sawing type tools that won't widen the string slots any. You may be needing to move the string up or down in a slot, not adding any free side-to-side slop. If the string is too low and needs to be raised in a slot, you can powder some bone or hard plastic, pinch some and stuff it into the slot, pack it in with the edge of a credit card, and touch a toothpick tip with a drop of super glue on it to the packed slot. let it dry thoroughly, clean up a bit and continue making checks and adjustments.

String Radius

   — 3. Are the string heights smooth from low, to high strings? And the right overall height for you?

      This is the final check and setup step. It varies based on the players choice and gauge of the string set chosen by the player. Any adjustments in this step will be made at the nut, and at the bridge. Heavy string sets will need more height for the heavier and subsequently larger string oscillations (vibrations). light strings will need lower height so tuned pitch will not go up too much as the string is pushed down to meet the fret. Presuming that checks 1 & 2 are complete, the nut (at the long end of the neck) is first up. Strings tightened up somewhat? Check each string at the first fret. Push each one down to the first fret one at a time and note how far each string has to travel before touching that first fret. The distance should be. . . not much. Just enough so there is clearly enough height so the string doesn't buzz when plucked open, and not so close that you have to look again to see if there is any string height from the fret at all. At the nut there won't be much difference between the fat strings and the thin strings in the height at the first fret. Not a lot of vibration there. There will be some difference at the twelfth fret and that height will be set by the bridge saddle (at the strumming end). Some people use the top or highest fret of the finger board for this check. I use the twelfth fret for consistency and because some finger boards on acoustic guitars take a dive after the heel-joint at the box.

Even String Heights       

Wrong!   Poor string heights. Check the Nut and the Bridge, notches and saddles.

      Once you are happy with the nut and first fret string heights and radius, you move to the other end. The bridge. It is usually resting free in a slot on acoustics and can be lifted out with your fingers after loosening the strings or removing them. If not, make it so. On the top, some bridges have only the notches the string has cut into it over time. Others are cut and shaped deliberately to set string spacing wider or narrower, and some are stepped forward and backward to adjust the string lengths individually to get the intonation of the whole set more precise. You choose (look at the width of your finger board closest to the bridge). Ask yourself, "Do I slide off the edge of the finger board when I bend strings?", or "Are they so close together I can't get my chubby fingers to press just one of them?". There are other questions you can come up with but this pretty much covers the basics. Back to the setup, you will be grinding the bottom edge of the saddle on fine sandpaper or an emery board laying on a flat table surface to lower one end, the other end, or both ends of the saddle while keeping the bottom (slot edge) strait and flat across it's length. If you take it down too much you will just have to get a new piece of bridge material and start over, so work slowly and put the bridge back in and tighten up the two outside strings, re-checking often. Again, do not over shoot or it's shot. Be conservative here and don't try to set a world record for lowness. You are tuning the two outside strings up to pitch, and plucking them to get the string set low without going too low and getting fret buzz. if it doesn't buzz plucked open than it won't at any fret either (with the first two steps done correctly). This is why changes in the order of the setup process is not an option. If the heights for the outside strings are good than the rest will fall in where they may unless you need to work one of the particular string saddle points to correct a fault. Sometimes the radius of the bridge will result in a flatter outlay than at the nut. This is called a compound radius. Usually reflected by a compound radius in the finger board as well, but not necessarily. Some players just like it flatter there for strumming, Others may prefer more radius for finger picking styles or even bow use.

Joined Top Pieces  

A difficult repair job. Quite lucky actually, being able to collect all the original broken pieces and get them back together.

      You can't really see many of the repairs. This soundboard was kicked in accidentally during a little surprise brawl at a beach party and the top split into nine pieces. Being my friends favorite 6-String for daily song work he asked me if I could please put it back together again for him, using the original pieces for MoJo. Since there was not much else that could go wrong, I went about removing the rest of the top, readying it for the repair while he sent someone back to the beach to retrieve one missing strip from the fragmented splinters of wood.

      I would not have thought the arch top on this old harmony guitar would have been made from anything other than plywood, but it was a solid top and the pieces seemed to fit together pretty well. It went back together one or two strips at a time since I wanted to be able to watch and handle each joint individually without getting too many going to do a good job. Eventually I held half a top in each hand and I could clear the bench and concentrate in the final center length single joint with blocks and clamps set to force it back to a flat rim with the arch joint tight and clean. A process of defining and pinning the rim to the final profile and piling books on to bringing the wood together on the top of the arch and close the center gap. I used an epoxy resin wood glue to make the split repairs, and a nice liquid hide glue to refit the top on the guitar so it could be serviced if needed later. I had very little scraping to do on any of the joints. It all fit back together very nicely. I had so much top finish scraped off that he decided he liked the look and had me scrape the whole thing down, opting for a hand rubbed tung-oil finish. A little hand stripping with white lacquer around the edge and it was done.


Fly By Wire

A problem unique to the Piezo Bridge on a Parker Fly Classic (Hard-tail) Guitar.


      Once when I changed the strings on my 1993 Parker Fly Guitar I noticed that one of the high strings would not sound (electrically). I thought something had gone wrong with that element on the Piezo pickup. The others sounded, but not that one string. What I found was that the individual piezo saddle button (with the string slot in it) sits on top of the ceramic piezo element saddleand is not connected electrically to the saddle or bridge, except for the string resting on it and grounding through the barrel end to the tailpiece. So I looked with a multi-meter to see if any of the other saddles were grounded, (all of six string-slots floated, no contact with the saddle). Saddles on newer Fly's I have looked at seem to have some sort of foil packing wrinkled around the button to make contact. PaintBallThe string set I had put on was D'Addario with (painted) color-coded barrels which broke the usual electrical contact with the machined aluminum tailpiece. I noticed that the saddle of the Piezo element needed to be grounded (by way of the string) when one of the other string wires I had not trimmed off yet at the tuners touched the offending string post, whereupon it grounded (through another string) and started sounding again. Use only strings with bare bronze or the newer anodized barrels and the problem never comes up. If you have no choice but to string up a set of D'Addario's with the painted barrels, leave the tails on at the tuners and braid them together to get through the night. The wound strings will usually have enough bale around the barrel to make contact with the tailpiece, but the light strings may just clear through, with only the barrel contacting the string hole for electrical grounding. Watch for it.

The Flex-Tapes in a Parker Fly Classic Guitar.


      Click for a larger view.
Parker Flex Tapes

      The flex-tapes in the first Parker Guitars were an almost mandatory step in the application and evolution of modern design techniques and technology's. With new technology coming out almost every day it makes people get all exited about what can be done and they just go out and do it, without even pausing to consider whether they should, or what will happen if it fails to perform as expected. I must admit I love technology but there are practical issues to think of before throwing a new idea into production.

      Unfortunately using flex-tapes in a guitar cavity resulted in a completely unserviceable design for the working world of the guitar player. I simply needed to tighten a loose pot and was very surprised when the tape simply tore like aluminum foil at the slightest stressing. I was even holding the back of the pot at the time and it did not get turned more than 15 degrees.

      I scraped down to the traces and patched over the three torn circuits with resister leads, and immediately began reverse engineering the entire guitar in anticipation of more problems with light weight components in what would be a heavily used guitar. I was going to reproduce these tapes and these drawings are to scale, but I decided to abandon the tapes in favor of point-to-point traditional wiring.

A Reverse-Engineered Full Schematic of the Parker Fly Classic Guitar.


      Click for a larger view.
Parker Fly Schematic

      Maybe my own work will help you some day. This is a schematic of one of the very early fly guitars. The newer Parkers have gone back to more traditional wiring and changed a lot of things since this issue was made. There are more out there though, so if you have one these older Parker guitars, this drawing will be of value. I have looked for full schematics and never found one that really got down to it. So here is the whole original design, reversed engineered and laid out for you.

      I have completely removed all the flex tapes from mine, made modifications to remove the master volume pot entirely as the function is redundant to the stacked volume pots for piezo and electric pickups which are placed much more out of the way. I also removed the red mono/stereo button switch, wired a new and sturdier stereo output jack. Wired it mono output, using the traditional ring-to ground for power switching with plug in. I removed the piezo/elect. selector since the blend is controlled and isolated in the on-board pre-amp already. I don't use stereo output, so that goes in favor of a simple and solid plug connection. I would use a pedal if I want volume swells so the little finger reach of the master volume is not desired as much as swing space for strumming. Of course my work is entirely reversible so as to allow the restoration of a true classic, (assuming it had new flex-tapes to rebuild it with). Anyway, here is the research on what is going on inside. You can decide what you want to accomplish with it.

Have an old Parker Fly that needs hand-wiring to replace a torn circuit tape,
reduce the controls to recycle components or remove redundancy?


Click for PDF. -
OEM Switch 4P-3T
Parker OEM Full
    Click for PDF. -
OEM Switch 4P-3T
Mod: Min. Wiring
    Comparison:-
OEM Switch &
Aftermarket Alt.
       Here are work sheets for pulling out the flex-tapes circuit wiring in favor of hand wiring. The first page examples the fully wired schematic using the original (OEM) Parker switch and showing all the controls in place. The second page shows a minimal configuration using the original (OEM) Parker switch. Explanation is given to allow you to remove parts and functions selectively and retain restorability with a do-no-harm policy. Pay special attention to the pickup wiring as there are different 4P-3T On/On/On three position selector switches you could run into. You will want to map out any switch you are not sure about. Do not just hook up pickup wires to any old switch with 12 lugs on it or you will be just guessing at the contact pattern. The trick is in understanding the mag-pickup switching. The Original Equipment Manufactured switch has an odd latch configuration and is not the same as other 4P-3T switches. So check difference like the ones shown in the comparison sheet and adjust your plans accordingly.
Flextapes   No Tapes

A Quick List of General Repair Tips:

      I will just throw these tips out and work on the details and more stuff later.

  • Scratches. Use toothpaste. It has a mild abrasive in it and cleans up with water. Test anything you use as a polish for a water cleanup before using it. If it does not mix with water, it is either petroleum based, or silicon based.

  • The silicon polishes give an artificially fast shine by filing in fine scratches, and glossing over the problems. It will not last and worse, it seals the finish from other treatments and repairs. It is hard to clean off and gets into cracks preventing glues, finishes, and other polishes and repairs from working. In short it contaminates any surface it is in contact with. I can not think of a single time in twenty thirty forty years of supporting guitar players where I have used, heard of using, read about using, or been asked to use any silicon product anywhere near a musical instrument.

  • Petroleum based polishes work by softening slightly, the existing (polyurethane) finish and pushing it back in to fill fine scratches. As you work, it dries and then takes on a new shine. You can smell it. and you will see it picked up on the polishing rag. Be sure you are working on a finish that is a petroleum base finish. Avoid using petroleum polishes on fine instruments finished with natural oils or water-based hand applied varnishes or shellacs. Natural finishes should be handled carefully and not contaminated. Just spend the time to polish them with a hand towel.

  • Dents. Again, know what the finish is first. (Assuming a polyurethane finish), try a drop if super-glue. Let it dry and reapply until there is enough fill to scrape down with a scraper blade. Then polish out fine scratches as above.

  • Electrical problems. The first place to look for electrical problems on acoustics with pickups and electric guitars is at the moving parts. It's always the moving parts. Scratchy sounds when turning the knobs, wiggling the plug, throwing a switch. These are the places where electrical contact is sketchy at best. Lick your cord plug and put it in again with a twist. Spit makes a good dielectric in a pinch. Later you can clean and lube things using the expensive stuff in the small spray can you get from Radio-Shack, (not a sponsor). It's called "Control/Contact Cleaner and Lubricant". Cat No. 640-4315. The reason for this is two fold. First, It works and lasts about a year between uses, so it is actually cheaper in the long run (don't let your friends run off with the stuff). Secondly, many larger cans of contact cleaner have no lube in them, can attack some finishes, and have so much pressure in a new full can that the freezing effect of the propellant is enough to actually shatter the cheaper clear-plastic armature inside potentiometers used as factory equipment in foreign assembled, low-end guitars. Boy can I be cruel. Yeah, that's right, the wood parts may be the same, but buy an American assembly if you want the good hardware on the outside and the good parts put inside.

Gibson Les Paul Standard (1968)

      This classic suffered a broken peg head from being stepped on. Broke it clean off. A simple broken wrist type split leaving a rather clean grain to work with. Someone had tried to repair it before and thankfully did such a quick job of it they neither fixed it, or messed up the damage much by trying. That gave me the opportunity to clean it up and fit it back together with waterproof Weld Wood® two part powder and resin epoxy which conveniently was dark plumb/burgundy like the finish I had to re-apply to the back of the neck. I went around for a week looking for an off the shelf translucent lacquer that would be close enough to use. I had about given up when I was looking in a local Fred Meyer department store for unrelated items and stumbled into the arts and crafts section. There I spotted the transparent plastic cap on a small 6oz can of spray paint. Sure looked like the right shade. What was it? It was tiffany glass fake paint beside the tube of lead-like putty to simulate that effect on some cheap glass. What are the chances it's lacquer I thought. I turned it around to see what it cleaned up with and read, "lacquer thinner". It worked out just perfect. Lacquer finishes have their own problems when trying to get a good one and it takes good timing and skill to avoid any fish-eyes or over working of the finish. The point is I was able to match it without needing to set up a full paint station to do it. The person I did this repair for said he later sold the guitar to Robbie Laws.

1968 Les Paul repair pix_01 1968 Les Paul repair pix_02
1968 Les Paul repair pix_03
1968 Les Paul repair pix_04 1968 Les Paul repair pix_05
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