PLEASE NOTE: The next 3 pages are under finish-up construction. Gathering and editing the information and pictures for these webpages takes considerable time which lags behind real time work. I have posted pictures and comprehensive info regarding tracing down 2 electronic faults found and cured. The pages are current to just prior to reinstalling a fresh electronics assembly. I have also provided schematics specific to this Supro steel guitar (it's factory original). I will add text details in a priority order as soon as I am able to. Additional pictures and info will be posted as soon I am able to.
These webpages are being constructed for my most-deserving Customer; Thank You. I also make such pages for guitars that don't have a lot of information published about them, such as Valco / Supro guitars, ...for the beneift of others that have work to do on Valcos / Supros or folks that just want to see inside "their" Valco / Supros and/or learn some techniques in working on guitars. I am thankful for countless people who have taught me so generously over the past 51 years. I enjoy working on guitars in detail and publishing work online when I am able to. It pleases me when it helps someone.
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~ 1948 Supro Lap Steel Cleanup and Repairs ~
Page 4; Electronics Cleaned Up, Troubleshooting & Repair:
Upon assembling and playing this Steel, I wasn't satisfied with some intermittence in the tone pot and in one side of the pickup. It's not unusual at all for electronic problems to surface once an old guitar is opened up and things moved around to detect faults on the verge of occuring. It passed the meter readings and tapping tests when opened up, but only playing will reveal full functionality. Time to take a look to find out what's intermittent.
This Steel's specific wiring chart; Factory original:
Notice that a 1 Meg aftermarket changeout of the tone pot and a chicken head knob was very common for boo-wah / wah-wah effects; Either as a factory mod or Dealer mod; Which one unknown.
Schematic of fault readings. See fault and correct readings below this schematic.
Readings are in ohms:
CORRECT READINGS SHOULD HAVE BEEN:
Between red points:
Reading across coil on ground side of pickup = 2.5K
Between blue points:
From pot wiper to output ground = 0 to 250K.
From pot wiper to pickup input into pot = 5K.
From pickup input to pot, to pickup ground = 5K.
Between Green points:
From pickup input to ground tap = 0 to 500K.
From ground tap to empty lug = 0 to 500K.
FAULT READINGS:
Between red points:
Reading across coil on ground side of pickup = Incorrect intermittant readings up to 1 Meg+.
Between blue points:
From pot wiper to output ground = Correct 0 to 250K.
From pot wiper to pickup input into pot = Correct 0 to 250K.
From pickup input to pot, to pickup ground = Incorrect 1 Meg+.
Between Green points:
From pickup input to ground tap = Incorrect intermittant 0 readings.
From ground tap to empty lug = Incorrect intermittent 0 readings.
SYNOPSIS:
(1) 1 Meg reveals intermittent open ground-side coil. (reading incidental aged pickup coil casing conductance to ground when open).
(2) Intermittent 0 on tone pot reveals wiper resistance-race worn out; Confirmed and not rebuildable.
See work confirming faults on the next page.
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TECH SCHEMATIC:
See Next Page; Troubleshooting >>>
