Eico Model 232 Vacuum Tube Volt Meter Restoration

The Eico Model 232 Peak to Peak VTVM (Vacuum Tube Volt Meter) was first introduced in 1954 both as a kit and a complete unit. This meter was revolutionary at the time because it could measure Peak to Peak instead of RMS AC voltage and it's high input impedance, 11 meg DC and 10 meg AC, did not load down the circuit you were measuring.  The assembled Eico Model 232 VTVM was used in many vocational electronic programs during it production years. In fact the Model 232 was still being used in my high school T and I (Trade and Industry) Vocational Electronic program in 1986! I found this fine specimen at a rummage sale and look forward to cleaning it up and bringing it back to original specifications.

Eico Model 232 Assembly Manual PDF Download

Step 1 Initial Testing

The first step was to determine if there were any initial issues with the Eico VTVM. I plugged it in and let it warm up for a couple minutes. I put the meter in the DC+ Function and 15Volt Range and was able to successfully measure the voltage of a 9 volt battery. In addition, I put the meter into Ohms function Rx10K Range and was able to successfully measure a 1K resistor. Note, it is important to put the Uni-Probe switch into DC position to measure the battery Voltage and AC/Ohms position for measuring a resistor's resistance. The only issues I notices were that the Zero and Ohms Adjustment Potentiometers were touchy, probably due to being dirty, and that the Rx100K and Rx1M scale did not work.  

Step 2 Cabinet Removal

Two screws, circled in red below, hold the cabinet of the Eico Model 232 in place. Once the screws have been removed, place the VTVM face down on a soft cloth then carefully thread the power cord through the center hole while pulling the rear cover up and off.

Look at this ancient D Cell battery installed in the VTVM! When was the last time a D Cell cost 20 cents?  The D Cell battery is a current source used when the meter is in the Ohms function setting.

Step 3 Test Vacuum Tubes

Unlike Solid State components, such as Diodes and Transistors, Vacuum Tubes have a finite life and should be checked using a Tube Tester.

Step 4 Electrolytic Capacitor Replacement

As electrolytic capacitors age, their electrolyte dries up causing their electrical capacity to drop and leakage current to increase. It is definitely a good idea to replace 50 year old electrolytic capacitors!

The Eico Model 232 uses a 10uF 150Volt electrolytic capacitor, labeled C5 in the manual, to filter the DC ripple from the power supply. 

I replaced C5 with a modern 22uF 150Volt Radial Capacitor I had in stock.

Step 5 Cleaning and Lubrication

I spray electrical contact cleaner into the open slots of the Zero and Ohms Adjustment potentiometers then rotate the knobs back and forth, full clockwise and then counterclockwise, to clean the wiper connected to the center terminal.

I then use electrical contact cleaner to clean the metal contacts on the Phenolic and Ceramic wafers that make up the Function and Range rotary switches. I spray the metal contacts then work the switch back and forth through each setting.

I use Labelle 107 model train oil to lubricate the shafts of the rotary switches and potentiometers connected to the front panel, then work the oil in by moving them through each position. Labelle 107 oil is great as it will not harm plastics parts like other lubricants. 

The Function and Range switch use a ball bearing under tension to produce the ratcheting action needed to lock you into each setting. I use Labelle 106 model train grease to lubricate the race the ball bearing travels on. Labelle 106 Grease will not harm plastic parts.

Q-Tips, moistened with Windex, work great for cleaning hard to reach places on the VTVM chassis. Look how dirty this Q-Tip is after an initial cleaning of the top of the chassis!

Mequiar's PLASTX, meant to clean and polish plastic car parts, also works great on removing the yellowing of a meter face cover! Note, this is a "before" picture of the meter face cover.

Step 6 Rotary Wafer Switch Repair

One of the ceramic wafer decks of the Range switch fell apart during cleaning, I suspect that it already had hairline cracks. This is probably the root cause of why the Rx100K and Rx1M Ohms Range didn't work!

I used Super Glue  (Cyanoacrylate) to adhere ceramic parts of the Range switch wafer back together. I then used nylon ties, wrapped around the circumference of the switch wafer, to add permanent strength. I clipped the ends of the nylon ties once the glue dried.

Step 7 Paper/Wax Capacitor Replacement

Paper/Wax capacitors deteriorate with age due to acid in the paper. I decided to replace them with modern Polyester Capacitors.

Here is the original .025 uF 400Volt Paper/Wax Capacitor, designated C3 in the Construction Manual. 

Here is the replacement .027uF 630Volt Polyester Capacitor replacement installed.

C2, as designated in the Construction Manual, was also replaced with a  .027uF 630Volt Polyester Capacitor.

Here is the original .003 uF 400Volt Paper/Wax Capacitor, designated C4 in the Construction Manual. 

Here is the replacement .0033uF 1600Volt Polyester Capacitor replacement installed.

Here is the original .1 uF 1000Volt Paper/Wax Capacitor, designated C1 in the Construction Manual. 

Here is the replacement .1uF 1000Volt Polyester Capacitor replacement installed.

Step 8 Cabinet Cleaning

In order to do a thorough cabinet cleaning, you must remove the three chrome button covers, that cover the calibration controls, on the side. 

I also remove the leather strap, it is held in place by two by a screw and nut on each side of the cabinet.

A thorough scrubbing in a dishwashing soap bath is in order to remove years of dirt, grime, and tar from tobacco smoke. Rinse then completely dry the cabinet when finished.

Mequiar's Motorcycle All Metal Polish works great for removing rust from the three chrome button covers. Note, this is a "before" picture of the button covers.

I apply two coats of Mequiar's Motorcycle Liquid Wax, buffing it with a chamois between coats, to get the cabinet to shine like when it was new.

Cabinet cleaning is complete, I then reattach the leather strap and installed the chrome button covers.

Step 9 Uni-Probe Repair

The insulator on the ground lead had snapped off.

I used Super Glue (Cyanoacrylate) to adhere it back together. The tie strap holds the assembly together while it dried. 

The Uni-Probe was in bad shape. It was held together with electrical tape!

Here is what I found when I removed the electrical tape. The Uni-Probe case was cracked and several pieces of the case fell off. The Uni-Probe contains an internal switch. You rotate the white part of the lead to the DC or AC/Ohms position depending on what is being measured.

I used rubbing alcohol to remove all of the electrical tape adhesive residue from the Uni-Probe. Then, I used Super Glue (Cyanoacrylate) to glue the pieces of the Uni-Probe case back together. A screw with a large head holds the innards of the Uni-Probe in place. This screw is insulated from the probe lead so there is risk of electrical if you touch the screw head while taking High Voltage measurements.

Step 10 Calibration

It is important to re-calibrate the Eico Model VTVM Model 232 after the Electrolytic and Paper/Wax capacitors have been replace. Consult the Eico Model 232 Instruction Manual for the calibration procedure. 

Eico Model 232 Instruction Manual Download

Calibration is accomplished by adjusting the AC Balance, DC Calibration, and AC Calibration potentiometers located toward the rear bottom of the chassis.

Performing Calibration on my restored Eico Model 232 VTVM!

Conclusion

With the help of inexpensive replacement capacitors, Super Glue (Cyanoacrylate), some common household cleaning products, motorcycle wax and polish. I was able to make this vintage Eico Model 232 VTVM shine and operate like the day it was built!