Fluke 29 Series II Problem

[M0UKD]

Hi all.

I picked up a Fluke 29 Series II in great condition. It had the common fault with the LCD zebra connections, which was easily fixed.
However, the meter has a strange issue, where some modes do not work.

Volts DC, Millivolts DC and Ohms/Capacitance ranges work perfectly. The issue is with VAC, Hz, Continuity and Amps ranges.

VAC: Displays a random Ohms reading, where probes do nothing. 
Hz: Displays a random mV DC reading with the same value as above and probes do nothing.
VDC: Works perfect 
mV DC: Works perfect
Ohms / Capacitance: Works perfect
Continuity: Displays an Ohms range, which probes have some effect. No continuity.
Amps: Displays a VDC range, which probes have some effect, but not volts or current.

I've had a look at the range switch, but cant see any obvious issues. No poking about will make these issues go away. I haven't took it off yet as that might be a last resort, but I'm not convinced the range switch is at fault.
Anyone have any ideas what this could be or seen this or a similar issue before on a Fluke? Maybe the microcontroller is at fault? Some photos are below.







Cheers, John.

[ModemHead]

If you don't already have it, download a copy of the service manual.

The problem looks like it might be related to the 3-bit function code supplied to the processor by the rotary switch.  Check the switch, the traces, and the pins on the chip.  Looks like F1 may be stuck high for some reason.  If I interpret the diagram correctly, a "high" is 0V with respect to ground (the COM jack) and "low" is Vss.

[M0UKD]

Thanks for that, that's a great help! I couldn't find the service manual, but didn't think of actually going to the fluke website!
I shall take a closer look and get back to you.

Cheers, John.

[retiredcaps]

My only value add here is that I noticed MP7 (+) is corroded from the picture?

C34, which is tied to pin 68 (F1) as described by modemhead, is close to MP7.  Any alkaline spilled juice might be affecting C34?

[retiredcaps]

I couldn't find the service manual, but didn't think of actually going to the fluke website!

Almost all the first and second generation handheld Fluke meters have service manuals.

For sure, none of the recent generation models have any publicly available service manuals.  Example, none for the Fluke 87V, but there is one for the Fluke 87 I (original).

[retiredcaps]

The problem looks like it might be related to the 3-bit function code supplied to the processor by the rotary switch.  Check the switch, the traces, and the pins on the chip.

BTW, modemhead has fixed something like this before. See

http://mrmodemhead.com/blog/fluke-23-iii-dmm-repair/

[ModemHead]

BTW, modemhead has fixed something like this before. See

You remember that stuff better than I do.     Good eyes on the corrosion, I missed that.

Here are the locations for F0, F1, and F2 on the switch.  A logic "0" will be about -3.2V (Vss).  A logic "1" will be about 0V.  Both measured with respect to the COM jack (ground).  The function code inputs are pulled up internally, so an open trace or switch contact would stick the associated bit high.

[M0UKD]

Thanks for all the helpful replies. Managed to get it working by giving the switch and the board a clean, will see how reliable it is.

ModemHead, the service manual really helped. I found F0, F1 & F2 are just over 5v for high and 2.5v for low, when the meter is working correctly (with respect to the -ve battery terminal).

Retiredcaps, yes there is a slight corrosion on the positive terminal although I couldn't see any evidence of it reaching the PCB, but have cleaned it up as best I can.

Thanks again for the helpful replies. The service manual is excellent for troubleshooting!
I shall probably sell my Fluke 115 and keep this meter. There's something nice about the old flukes (or maybe because I'm getting on a bit!)

I might make a video on this meter at some point, there don't seem to be much on the internet about the 29/79's.

Thanks again 

[ModemHead]

Excellent!  I have fixed many DMMs myself with little more than isopropyl alcohol and a toothbrush.

The 79/29-II is a nice 70-series meter with more functionality than the more ubiquitous 77 family.  The worst thing I can say about them is that the LCDs have a limited viewing angle.  The model 76 has the same feature set as the 79/29-II but adds True RMS.

BTW, thanks for putting effort into your original post, to take clear pictures and give a good description.   

[retiredcaps]

Retiredcaps, yes there is a slight corrosion on the positive terminal

This

https://www.digikey.ca/product-detail/en/keystone-electronics/636/36-636-ND/316556

or

https://www.digikey.ca/product-detail/en/keystone-electronics/594/36-594-ND/96741

might be a replacement.

Maybe put it on your next order to digikey or mouser?

[retiredcaps]

BTW, thanks for putting effort into your original post, to take clear pictures and give a good description.   

Yep, it helps a lot and a refreshing change from

"Help me.  this is broken."

which implies the poster has done no homework, research and expects us to hand hold him/her through the entire process.