Fluke 77 DVM

[N_Cook]

Otherwise trusty meter, whenever I try on a Weston Cell it is always the
same voltage registered. But now on the ohms scale will sometimes read
10 or 12 meg with no probes in place. Good battery.
Something to do with the screen shielding? Without any metal covering,
ie the top cover removed and no replacement for the now missing sticky
backed foil over the shielded tinplate box, the meter will not pass
POST, all segments lit on display permanent and no beep on changing
rotary sw setting, normal ?.
So start with cover in place , turn to ohms, and remove cover , it goes
to the floating 10s of megs. Twizzle sticking does not show suspect
switch , preset or anything, and gradually drifts to over-scale, >30M.
Something going leaky with age?

[N_Cook]

Since the last time I looked Fluke has placed the SM and schematic out there
http://transmille.net/ProCal/Procedure%20Library/Fluke%20Digital%20Multimeter%2023%20MKII%20%5B1.10%5D/Technical%20Data/Fluke%2070%20Series%20MKII%20(PN%20896204%20July%201991%20Rev%201,%2009-92)%20Service%20Manual.pdf

[mike]

Did you try cleaning the gunk out of the probe sockets?
Probably have to remove the board.

Some meters have a split contact in the socket that sets off an
an alarm if you try to measure volts with the probe in the current
socket. Gotta be some voltage somewhere to sense. Can that
leak thru socket gunk?

[Phil Allison]

"Nutcase Pommy Kook" <div...@tcp.co.uk>

> Something going leaky with age?

** It's covered in a thick, sticky layer of your asinine bullshit.




.... Phil

[William Sommerwerck]

I would simply flush out everything inside with contact cleaner. It's more
likely to be an accumulation of schmutz, than something wrong with the
electronics.

[N_Cook]

The uk has been permanently damp for about 2 months now. Perhaps
something has gone hydroscopic. Brushed meths over both sides of the
lower part of the pcb and allowed to dry off. Much the same 10s of megs.
When powered up and open I played a distant hot air gun over the dvm,
held in hand at the time so only hair drier temp and the o/c ohms
suddenly dropped to 10s of K . Let it cool down and gradually went to
>33M and repeated switching on/off the last few times has stayed that way.
Reminded of a batch of Marshall amp pcbs that had contamination inside
them combined with damp perhaps and marked increase in conductivity with
relatively slight warming of the pcb, but HV there in that case

[William Sommerwerck]

"N_Cook" wrote in message news:lb8t8s$l63$1...@dont-email.me...

On 16/01/2014 13:45, William Sommerwerck wrote:

>> I would simply flush out everything inside with contact cleaner.
>> It's more likely to be an accumulation of schmutz, than something
>> wrong with the electronics.

> The UK has been permanently damp for about 2 months now. Perhaps

> something has gone hydroscopic. Brushed meths over both sides of the
> lower part of the pcb and allowed to dry off. Much the same 10s of megs.
> When powered up and open I played a distant hot air gun over the dvm,
> held in hand at the time so only hair drier temp and the o/c ohms
> suddenly dropped to 10s of K . Let it cool down and gradually went to
> >33M and repeated switching on/off the last few times has stayed that way.

Glad to hear the patient is improving. What about the switches and the jacks?

[N_Cook]

When the dvm was in errant mode , saying say 15Meg, stressing rotary sw
wafer or sockets etc with a plastic pen barrel made no marked change in
the reading, wavering much the same +/- 10K or so, long term wavering
10M to 20Meg, whether twizzling or not. Will see tomorrow if the ohms
scale opens at 10s of megs rather than >33 megs

[bud--]

http://transmille.net/
gets you into the directory structure with access to other strange and
wonderful stuff including a calibration manual for Fluke 187/189

[Michael Black]

My DMM acted like that at one point, and I took it apart, thinking the
switch was dirty. But no.

It turned out the fuse was bad. It still had continuity, but not zero
ohms. A new fuse fixed the problem.

Michael

[Shaun]

"Michael Black" wrote in message
news:alpine.LNX.2.02.1...@darkstar.example.org...

There is also a resistor that fuses open (fusistor) when too much current
flows. It's usually light brown or blue in color near the input jacks.
It's either 1 Kohm or 1 Megohm. It has been over 18 years since I worked on
these so all the details arn't clear. If it's blown, it will give funny
reading too. For cleaning the PCB - use electronics grade Isopropyl alcohol
and a new clean tooth brush. Scrub the board top and bottom near the input
jacks, then rinse with more alcohol and let it dry properly.

Shaun

[N_Cook]

I've had that failure before on another Fluke and the symptom then is
that readings are about 1 percent of what they should be, no wavering.

Another rain-soaked night in the UK, but trying out this 77, shows
>33meg for open probes and Weston Cell reading 1.017V (on DCV scale) as
it always has been over 20 years and using the same cell

[N_Cook]

well over a week on of daily use and no return to wavering digits