Victor VC202 - Replacing broken LCD with two dual-digit eight-segment Leds

[WolfmanTech]

This is a meter I got for free years ago when I was taking a summer electronics class, after I fumbled it and the screen broke when it hit the floor. Since it has transistor checking and some capacitance checking ability, which my other meters lack, I figured I might as well try to repair it. I've got what seems to be a fairly close match of the schematic and I've found the data-sheet for the display driver- a 7106 -but I've yet to determine if it can drive an Led display. Pictures and links to relevant data to follow, after I get a nights sleep, but I wanted to give folks here a chance to weigh in with constructive criticism/suggestions and/or obvious problems with building it this way. Thanks in advance! I'll probably be posting a lot of other posts about the various junky old test equipment I've managed to aquire over the past few years, most of it free!

[WolfmanTech]

Hmm, so I'd have to get a 7107 to install after cutting the potted 7106 off the board... As for the TT, I have an older analog tester purpose built for such, so I'm mainly interested in the Capacitance testing functionality. Then, of course, there's the can it be done/can I do it motivation, y'know? That said, thank you for your input!

[janoc]

Hmm, so I'd have to get a 7107 to install after cutting the potted 7106 off the board... As for the TT, I have an older analog tester purpose built for such, so I'm mainly interested in the Capacitance testing functionality. Then, of course, there's the can it be done/can I do it motivation, y'know? That said, thank you for your input!

That's a good motivation, but considering you can get a pretty much identical meter for a few bucks at a hardware store, it really isn't worth the effort. Time is money!

[WolfmanTech]

Sadly, I'm not currently in a position to trade my time for money, so having a project to keep me busy is fairly important. As far as a meter for a few buck at a hardware store, oh if only that were literal... Still, I've collected so much electronic scrap/junk/parts that what I really need is a brilliant tinkering partner to come up with uses for this stuff! I could fill a warehouse with the stuff I could pick up for free in this city! Unfortunately a portion of what does make it to a recycling drop-off point, is sent to the dump! It irks me, but there's only so much I can collect and I've reached that point where I need to get rid of things without collecting more. Hell, I could build several TVs/Monitors with all the parts thereof I have. Anyway, this project will probably stall here until I look into a 7107 for it. Probably should drag out my old 15-mhz analog(?) crt-type o-scope to see if I can get it dialed in and working smoothly with some help from here. Until then. Keep tinkerin'!

[anachrocomputer]

Here's an example of an LCD (in an Fluke 8060A) that was replaced with LEDs:

http://mrmodemhead.com/blog/a-very-unique-fluke-8060a/

Modern LEDs are able to work on very low currents, low enough that LCD drivers can light them (just). So, maybe it can be fixed! If you do fix it, be sure to make a blog post showing how you did it.

[edavid]

You can drive an LED display from an ICL7106, but:

• you will need to add a driver from the 7106 backplane drive pin to the LED common pins, so you get the right segments lit
• segment drive is only 2mA, and the segments will be on 50% of the time, so you will only get 1mA average
• refresh rate will be ~60Hz, so expect flicker
• battery life will be bad
• you can't use 2 digit multiplexed displays, you would need 4 separate digits

Maybe it would be easier to find a replacement LCD.

It sounds like the 7106 is COB, so forget about replacing it with a 7107.

[SeanB]

Another caveat of the 7107 is that while it is almost the same pinout as the 7106, there are 2 very different pins. Power is only allowed to be 5V, not anything between 4 to 9V, and the common pin ( which was BP on the 7106) is likely to have 100mA of current flowing in it. As well you need a -5V rail, which is required to be as well regulated as the positive rail, but it can be made using the on chip oscillator and a pair of CMOS inverters driving a diode voltage inverter so you only need a 5V rail.

Another caveat is the chip using the on board reference is going to have issues on display counts, as the drivers heat up the chip in operation. Most common is an input just short of full scale, where it will blink slowly between 1999 and -   as the die alternately heats and cools.