Fluke 73 Repair

[Stormrider]

I got an older, broken Fluke 73 cheap awhile back. First time I looked at it i found R1, the 1Kohm fusible resistor, was open circuit. I dropped a regular 1K 1W part in it's place and the meter seems to work fine. Obviously, until I get the right replacement I'm not going to use the meter.

Owners manual calls it a 2W fusible resistor... Is digikey part# PPC1.0KDCT-ND suitable? Any better suggestions?

This one: Digi-Key - PPC1.0KDCT-ND (Manufacturer - NFR0200001001JR500)

[bob91343]

Call the Fluke tollfree number. They can tell you what to put in there.

[Findm-Keepm]

The 1K fusible resistors go bad if you "juice" the meter when in the ohms or diode/continuity function. The resistor is there to protect the current source that is used in the ohms/diode/continuity function.

Early (series "I") meters used an IRC BWF wirewound fusible resistor - looked like a 1 Watt resistor, but was rated at 2 Watts. Later series "II" meters used a Dale CMF-65 film resistor. These are available commercially, but in quantities of 100 minimum.

Fluke muddied things for a while with three different part numbers, but finally assigned one part number to replace any of them - 832550. Hard to find, but I got two from Fluke back in December. The ones I got looked like metal film resistors with a couple of color bands. 1(800) 90-FLUKE (1(800) 903-5853) gets you to the right people.

We used to replace them by the dozens in the cal lab when I was in the Navy. They also used the same resistor in the Fluke 5220 calibrator.

Cheers,

[bob91343]

What's the resistance value of this part?

[Findm-Keepm]

1000 ohms, 1%. The early (series "I") resistors (R1 on the schematic in the manual) were 5% devices. Accuracy of the instrument is not obtained from these resistors, and the subsequent metal film devices (used in the Series "II" and others) simply were supplied in 1% tolerances as is the industry standard for metal film resistors.

Here's the rub - for troubleshooting, I once put in a 1K, 1 Watt 2% flameproof resistor and verified my Fluke 75 was working. Mind you, the resistor is FUSIBLE, so the original brings a margin of safety and protection. I ordered the part (474080 in my early Fluke 75 series "I", now 832550) from the local distributor, and replaced the resistor. All was well. My original problem was the ohms indication would alternate between a reading (that was incorrect) and "OL"

Cheers,

[bob91343]

Thanks Brian; I once had to replace mine. I called Fluke and they said they had some ridiculous minimum order and I whined and cried on the phone so they sent me one free. I don't think that can happen again so I will have to buy something else if there is a next time.

I caused the problem by trying to measure the high voltage on my ham radio linear amplifier, which is well over 3 kV. I now know better.

[Stormrider]

Thanks Findm-Keepm and Bob91343; I'll contact Fluke and see what they have available.

[imix500]

I blew up the front end protection in my 87 and ordered the parts in flukes online store. Minimum order there as well (it might be lower than phone ordering?) but I just bought a few extra fuses to hit it.

[jlovda]

I just obtained a Fluke 75 (version I believe) for $10 at a flea market. It is very clean and the DC voltage function seems to work fine. The problem is that for low resistance values such as 1, 10, 100 up to about 1K ohms, the meter is way off. Usually about half the actual value. Above 1K the readings are within the tolerance level of the resistor. I measured the large fusible resistor you noted and it is about 1K ohm with out lifting one side off the board. One other interesting thing on the board are several red devices that look like tantalum capacitors but they are cut/sliced down the middle What are they? Any suggestions where to look. Anyone know where o get a free schematic off the internet? Thanks