hp e2378a dvm

[wings515]

I  was doing some thermostat measurements with the device under test in the freezer.  The DVM was situated on top of the freezer and I did not tell my wife it was there.  She opened the door and the DVM came crashing down.  Now the resistance measurements only show OL and 0.00 no matter what resistance I place across the leads.
The DC and AC voltage measurements are correct and the Audio continuity test is functional.
I have not tried the Diode test yet but will get to it some time today.

Any thoughts?  I know this is a very old DVM but it was given to all HP field System Engineers to promote the On Site product line.

I opened the DVM and there 'appears' to be something missing labeled "PTC".  The leads soldered to the PCB are about 3/8" apart and there is a residue of solder on each flat piece of material on what would be the ends.  It looks like something was between these two posts and has either broken or shattered.  I did not see any residue of a part in the case.
The location is next to the larger brown ceramic cap.

Regards,
Dan Kahn

[Swake]

Apparently the HP is a rebranded Yokogawa 7534-03 Multimeter.
A 'PTC' is a positive temperature coefficient resistor. Found a picture somewhere on the net of that 'black' component.

However no value.

Manual and specs of the meter attached

[Swake]

2 other sources show a pink component.

Also visible in this post: https://www.eevblog.com/forum/testgear/teardown-of-a-rebadged-yokogawa-()-multimeter/msg976538/#msg976538

Still no indication of value.

I think you'll have to search in documentation of other meters for something similar.

[andersthuresson]

A PTC in this application would normally be a part of protection. The resistance of a PTC get's higer the warmer it becomes. If you didn't find any loose parts or residue it's likely that it's been missing even before your issue happened. Since your meter been exposed to mechanical force I would suggest you look thru the PCB board carefully. Look for broken PCB traces, cracked components or cracked solder joints. I assume it worked fine before the unfortunate incident which should point towards a mechanical fault of some kind.

In resistance mode or diode mode the meter will output a test voltage. Check it that is present when switching to resistance mode or diode test mode.

[floobydust]

Quoted here from another thread, to keep the discussion here:

I dropped my 2378 DVM and a part labeled PTC became disconnected.  The markings are TDK 9309.  I purchased a non working 2378 and removed the TDK park.  This one had markings TDK 9009.  I installed the 9009 into my working 2378 but it is not installed correctly. One of the lead ends became unsoldered and the repair is not very well done.
The fault I had with the missing part was in the Resistance function.  It would only read OL or 0.00.  Now it reads correct resistance values, I tried a 500 ohm resistor. 
I would like to install correctly a new PTC but I am unable to find a replacement.
Anyone have a part number and a supplier for this part.  I think it is a temperature controller resistance.
Regards,
Dan Kahn

You need to know the PTC cold resistance. You could measure the resistance end-end of the piece that broke.
Today 1,100Ω is commonly used by Fluke and 1,500Ω ohms in the low cost chinese meters. To give a ballpark value. It's not critical. Out in the wild I see 500-3,500Ω used.
Pics show two styles of PTC in your meter, a long square part with no epoxy coatings or a black disc in the Mr. Modemhead pics.

From the user manual, max. voltage. rating on Ohms is 500V so a 600V PTC looks reasonable. There are few PTC's that are rated for 600-1,000V on the market, only two manufacturers of decent parts that I am aware of.