Need New LCD for Old B & K Bench DVM

[rotatepod]

B & K Precision - Model 2834

This bench style (120 vac, no batteries) was a real workhorse
for many years. When SMDs came along it was easy to
incorporate all the advanced functions this old meter has into
a portable battery powered unit.

Except for the display, all meter functions work normally. Several
segments on the display are fading. The circuit boards look so
good you would think this DVM was built recently! I cleaned the
rubberized switches with a contact cleaner.

Finding a needle in a haystack may be easier than locating a
replacement display for this DVM. I'll probably keep it even if
I can't replace the display.

Any help finding this part would be appreciated.

Thanks guys.

[Bigglez]

Greetings (No Name Supplied),

B & K Precision - Model 2834
..... Several segments on the display are fading. The circuit boards look so
good you would think this DVM was built recently! I cleaned the
rubberized switches with a contact cleaner.

How is the LCD glass module attached to the PCB?

Often these use conductive rubber strips. Over time the
contact resistance can increase and open circuit
the segment(s).

Comments Welcome!

[Bob Scott]

Except for the display, all meter functions work normally. Several segments on the display are fading. The circuit boards look so good you would think this DVM was built recently! I cleaned the
rubberized switches with a contact cleaner.

I'll probably keep it even if I can't replace the display.

I have never succesfully disassembled an LCD display. Once the glass LCD panel is removed from the conductive rubber contacts, the diplays never work again. Has anyone else been successful?

You might investigate the possibility of incorporating a standard compact 3-1/2 digit panel voltmeter. Most of these read 0-200mv and other ranges (2V, 20V, 200V with added attenuators or built-in attenuators switchable simply by shorting an appropriate contact to ground. They are priced starting about $10. Upwards if you need a backlight.

Two kinds are available. Common power supply where the input voltage and the diplay electronics can share a common ground and isolated power supply where your 200mv ground cannot attach to the meter power.

These meters all seem to contain the very old Harris/Intersil display driver OR an identical function clone: an epoxy blob that converts 0-200 mv right to the display.

If your B+K meter contains this chip, just wire around it. Find the ICs 0-200mV input and redirect it to the new panel meter.

Bob

[haklesup]

Such a paradox: How do you fix your broken test equipment when you need to use it to fix itself.

The elastomer connector (rubber strip) should form a gas tight seal with the glass and PCB and under normal use, does not oxidize or build up resistance. Normally you shouldn't disassemble the display unless there is evidence that it has been misaligned. THe contact surface on the glass is very fragile and alignment and compression are critical

On the other hand, a few faded segments does resemble poor contact. It could just as well be a partial failure of the display driver IC.

If the display is multiplexed (and it likely is) then a poor contact to a segment should show up in a predictable pattern in the other digits same segment.

Which segments are bad, does it follow a pattern within or across the digits. If its totally random or localized to a region, it may be a failure of the LCD or its seal.

Measurements of the segment and digit voltages from the driver IC would be a better non destructive test before tampering with the display glass.

[rotatepod]

This instrument was not your ordinary DVM. It was a full blown
4½ digit multimeter. It had all the advanced features that were
common in laboratory grade meters. I think it cost $450.00.
It had features like peak hold, relative, temperature, period,
frequency, etc. B & K described it as a bridge between their lab
meters that cost many thousands, and a very advanced hobby
meter. They were right!

The segment failures appear to be random. I can't replace the
display with a generic unit because I would lose all the icons and
descriptive words (PEAK-H, etc.) that are unique to this model.

I don't want to throw this meter in the trash or give it to a recycling
company. If I have to I'll box it up and store it in a closet. It meant
a lot to me many years ago when it was new and exciting.

[Janitor Tzap]

rotatepod,

I did a little checking on what this Model 2834 costs.
I was finding units still available for $1500.00!!!

I would check with B&K.
1-(800)766-1212
Ask what they would charge to replace the LCD screen.
If it's at least 1/4 the cost of what you paid new for it.
Then I would say go that route.

Or just ask them if you can get the LCD Screen Assembly, and replace it yourself.


Signed: Janitor Tzap