FLUKE 8024A Repair

[ronsr333]

Need Advice! Picked up a Fluke 8024A (No display). Installed a new 9VDC battery,  checked connections from the battery through the On/Off switch to U8. Full battery voltage is present at Vdd/Vss at U8. Need suggestions as to where to go next. Check electrolytics, take display apart and clean??  Clean and reseat U8? Any help?

[retiredcaps]

On my Fluke 8020A, I get about 2.65VAC on the lcd at 50Hz.  On my Fluke 75 II, I get about 1.55VAC on the lcd at 64Hz.

I'm not sure what it is on the 8024A, but see if there is any ACV and the frequency?

I would also take apart the lcd assembly and clean it with IPA.

[ronsr333]

Thanks for reply. Taking today off (Sunday). Will do on Monday and let you know how I make out.

[ronsr333]

retiredcaps:  What pins on the LCD did you make the AC measurements??

[retiredcaps]

retiredcaps:  What pins on the LCD did you make the AC measurements??

On the 8024A, it might be different.  A rare chance for me to "justify" a dual display meter.  My black probe is connected to the 9V battery negative terminal.

[ronsr333]

retiredcaps:  I am measuring 2.98 vac on the same pin as you show. I think the 8020 & 8024 both use the same intersil chip. Can't find my frequency counter to measure the frequency. Will provide frequency when I find it. I think that having a good reading here means that the U8 chip is probably working and that the problem is either a bad connection on U8 or in the flexible connector to the LCD. Will try to take apart the LCD assembly and reseat U8 and clean all contacts. I assume IPA is a good cleaner here.

[retiredcaps]

Will try to take apart the LCD assembly and reseat U8 and clean all contacts. I assume IPA is a good cleaner here.

Yes, use IPA.  Let it dry thoroughly before reassembly.

[retiredcaps]

Since Fluke and Intersil co-developed the 7106, the datasheet for the 7106 shows a test pin (pin 37).

In the Intersil 7106 datasheet, there is a way to do a "lamp test".  I'm assuming this will work for U8?  If it does, it at least confirms the lcd itself is okay.

I haven't done this myself so I don't know if it is a valid test or not.

edit: Found a nice website that shows how to test.

http://www.petervis.com/meters/ICL7106%20and%20ICL7107%20Digital%20Meter/ICL7107%20LED%20Display%20Settings.html

[ronsr333]

While apart, I have measured the resistance of the conductivity of the elastomer ("zebra")  connector. I am getting a pretty high resistance 2K on most of the conductors. Is this normal??

Ron

[SeanB]

Normal, as the LCD is mostly a capacitor. The backplane is a low frequency, typically between 20 to 100Hz depending on the design.

[ronsr333]

Thanks Sean B.  Awaiting a new ICL7106 A/D Converter; purchased on ebay. I intend to boil the Zebra connector (as suggested in another post) and try again to see if anything works. Be back after.

[retiredcaps]

The history of the 7106 and how Fluke and Intersil are involved is detailed below.

https://www.eevblog.com/forum/testgear/old-fluke-multimeters/

https://www.eevblog.com/forum/testgear/old-fluke-multimeters/msg319838/#msg319838

Thus, the 7106 is not an exact drop in replacement for the Fluke IC.