Vintage Keithley 130A teardown

Introduction

The latest addition to our vintage collection is a Keithley 130A handheld DMM from the mid-eighties.Keithley is not well known for its handheld DMMs, or at least I’ve never heard of them. It’s a 3.5 digit 0.25% instrument made in mid 1980s

Taking apart and cleaning

The meter came in a carry case with probe. Unfortunately both were in a very rough shape, raining tons of foam particles once opened. So they had to go.

Crusty old probes and case

Crusty old probes and case

Meter face coated in pieces of case

 

It even turns on!

It even turns on!

And of course the battery was left inside, for who knows how many decades:

Battery from yesteryears

Battery from yesteryears

Fused to the case!

Fused to the case!

Battery out

Battery out

Serial Number- does anybody know how to decode them?

Serial Number- does anybody know how to decode them?

Fuse compartment door

Fuse compartment door

Nice touch- a pull tab for the fuse

Nice touch- a pull tab for the fuse

The insides are not looking too bad- mainly coated with case foam particles and with some corrosion wicking up the battery wires. Surprisingly, there is not much there: A Maxim ICL7106  of 1985 vintage in a socket, Ti TL061CP JFET opamp, and a Motorola MC14070 Quad X-OR gate. The rest is mostly 0.1% resistors, two very nice rotary switches and some diodes, transistors and caps. They did use a few precision resistor networks though, which are a bit less obtainable.

Case open

Case open

Dual size fuse holder

Dual size fuse holder

10A range sense resistor

10A range sense resistor

TI TL061- still being made

TI TL061- still being made

Corrosion on the divider network

Corrosion on the divider network

A very obvious 0.1% :)

A very obvious 0.1% ūüôā

Back of the board

Back of the board

Worst area on the back

Worst area on the back

This required some serious scrubbing with alcohol, followed by touch up with a soldering iron and flux to get through the corrosion. While at it, I’ve changed the battery connector and wires to a new set.

As clean as I could make it without full immersion

As clean as I could make it without full immersion

Clean back of the board

Clean back of the board

Moving on to the display, it’s a typical LCD with a ¬†zebra strip connector

All contacts got a thorough cleaning with alcohol.

With all electronics out, it was a good time to give the case itself  a nice bath in warm water and soap:

Bath time!

Bath time!

The results exceeded my  hopes- things look brand new despite being almost 30 years old:

Top case looking brand news

Top case looking brand new

Bottom case

Bottom case

Very cool knobs- note the alignment mark on both sides

Folding stand with a brass screw

Folding stand with a brass screw

Case bottom with both covers

Case bottom with both covers

Case bottom- inside view

Case bottom- inside view

All parts

All parts

The mechanical design is pretty simple, but well thought out, so putting the unit back together was a very simple task:

As good as new

As good as new

Calibration and conclusion:

As described in the ¬†user manual, calibration entails applying 190mV to the¬†inputs with the meter set to DCV range and adjusting the lone potentiometer until the screen readout matches that number. In this unit I was not able to get close to that. Looking over the schematic, it appears that the culprit is most likely the heavily corroded resistor network near power connection- it contains resistors used to setup reference voltage. I can certainly chase that down and fix it, but it’s not worth it. At this stage I have in my hands a nice museum piece for showing and admiring but no longer for any meaningful measurements, so if the readings are off by a bit- big deal.

Schematic

It's alive!

It’s alive!

Resources:

 

 

 

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