Fluke 8020A blown fusible resistor...

[knockbill]

   

    I was checking ACV with this meter and it stopped reading , opened it up and found a piece of a resistor loose in the case,,, Schematic showed it to be R1 or R2, which are the same value (1K/2W) on the schematic, however the one that blew is color coded Br-Blk-Red-Sil-Blu which seems to be 1k/10%,,not sure what the Blue band is for at the end tho... The other one is color coded Br-Blk-Yel-Sil which seems to be 100k/10% (reads 82K)...

  Questions,,, Should they be different, or was someone in here before I got the meter? What do I replace it (them) with?
    Neither AC or DC functions work,, but Ohms is OK... It looks like one resistor is for Ohms range and the one that blew is for Volts...

    Thanks for any insight or help...   Link to manual/schem...   
http://exodus.poly.edu/~kurt/manuals/manuals/Fluke/FLUKE%208020A%20Instruction.pdf

Regards,
John

[Excavatoree]

The resistors are the same on the random 8020B I took from my pile of 80xx meters.    I'll see if I have an 8020A.    I'm not sure if the 8060 schematic you linked to has the same resistors or not.

[Excavatoree]

I found an 8020A in my "working" pile.  Resistors are as you describe.

[knockbill]

Thanks,,,
I didn't notice I posted the wrong  manual... Is this resistor a Fluke part, or can i get it from Mouser?

[Excavatoree]

The manual (8020a, I can't believe I have it)  doesn't indicate they are anything other than ordinary resistors.

From the manual scan I have:
R1 100K 1 watt  10 percent
R2  1K  2 watt   10 percent

I can't explain why one is listed as 1 watt and the other 2 watt, they are identical on my 8020A.   Maybe one of our repair experts can verify.  They both look like 2 watt resistors to me on two 8020s, an 8020B, and an 8021b that I was able to examine.

[knockbill]

Yeah,,, they are both 2W( I think) in my meter also...  I'll see if anyone knows for sure what it takes, before I use a common one...

[retiredcaps]

I was checking ACV with this meter and it stopped reading , opened it up and found a piece of a resistor loose in the case,,,

@OP, how high was the ACV that killed the 8020A?  1500V? 2000V?

The correct manual for the 8020A is

http://exodus.poly.edu/~kurt/manuals/manuals/Fluke/FLUKE%208020A%20Instruction.pdf

The all important errata manual is at

http://assets.fluke.com/manuals/8020a___imeng0003.pdf

with the following important information on page 2 (cut and paste shown)

R2, a fusible resistor, rated at 1k ohm, 2W can be sourced from modemhead's blog entry at

http://mrmodemhead.com/blog/fluke-87-fusible-resistor/

[retiredcaps]

Neither AC or DC functions work,, but Ohms is OK... It looks like one resistor is for Ohms range and the one that blew is for Volts...

For test purposes, you can solder in any 1k ohm resistor and see if that fixes your DCV and ACV problem.

For the ACV test, I suggest 120VAC or less  until you get the proper fusible resistor. 

[retiredcaps]

The other one is color coded Br-Blk-Yel-Sil which seems to be 100k/10% (reads 82K)...

You may want to verify that 82K om reading by desoldering it so it is out of circuit.  You might have also blown a MOV or two?

But, as a first step replace the obviously bad 1k ohm resistor first and then retest to see if DCV and ACV works or not.

[knockbill]

Thanks for the info,,, I was just checking  the meter as I usually do with a 9V  battery for DCV and then 120VAC+ line in, just to confirm teh V scale is not grossly out of  whack before I use it...
Was thinking of clipping in a 1k just to check the functions before throwing any parts at it,,, I can use a battery for confirmation, I guess... I'll stay away from line or higher V  until I get the  proper parts...

EDIT:  I clipped in a 1/2 W metal film R I had and tested a battery, seems to be all that is wrong with it,,, question is, do I have to go to Fluke for proper replacement,or is it something Mouser will stock ?

[Excavatoree]

Thanks, RC.  That didn't look right, and I've seen 80xx meters repaired with the moder, fusible resistor.  It seems difficult to source in the U.Ss, not sure if Canada is different.   The last time I tried to source the one Modemhead listed, it was unavailable.  The part I used to buy is also unavailable.  I've been lucky enough to find enough NOS parts from fluke distributors, and using pulls, I've JUST been able to repair the "oops" meters I've purchased. 

knockbill - .  I don't believe Fluke stocks these, but since you have the part number, you can ask.  Their parts people won't look up part numbers anymore, but if you have a p/n they will tell you cost and availability.  I can sell you two used resistors, if you'd like - PM me if interested.  As you can tell, I've got a few lying around. 

[retiredcaps]

EDIT:  I clipped in a 1/2 W metal film R I had and tested a battery, seems to be all that is wrong with it,,, question is, do I have to go to Fluke for proper replacement,or is it something Mouser will stock ?

As I mentioned earlier, modemhead's blog has this information.  Moyer Electronics.  Call them to see if they have stock.

http://www.moyerelectronics.com/BVModules/ProductTemplates/MoyerProductTemp/Product.aspx?productid=37a1f44f-b860-407d-93b6-a7601a4423d8

[ModemHead]

The last time I tried to source the one Modemhead listed, it was unavailable.  The part I used to buy is also unavailable.

The Vishay or the NTE?  The NTE one seems to be available still at Moyer, at 2/$1.00.

I'm away from home right now so I can't look at my 8020A, but I seem to recall both R1 and R2 were carbon composition.  The parts list calls out R2 as wirewound.  The revision notes indicate a part # change for R2 at rev F, so that may explain the inconsistencies.

[retiredcaps]

It seems difficult to source in the U.Ss, not sure if Canada is different.   The last time I tried to source the one Modemhead listed, it was unavailable.

The Vishay's are sold out, however, I know modemhead still has some Vishay's left over.  I got mine from Moyer. I ordered 5 packs for repairs.  I don't blow the input protection myself, but fix other people's oops.

[knockbill]

Thanks for replying,,,,
Yep resistors are 2/1.00 but shipping is 7 bucks,,,   I'll wait and see if I can scare these up locally,, now that I know what the problem is...
Thanks to all for the info...

[ModemHead]

Yep resistors are 2/1.00 but shipping is 7 bucks,,,

I was in email contact with Moyer about availability, and the rep offered to put them in a USPS envelope for me, so they only charged my card $2.00 for postage instead of the $7.  Might be worth asking, they seemed quite friendly even though I wasn't ordering hundreds.

[knockbill]

Thanks,,, that's more reasonable...

[knockbill]

Update,,,
I put a 1k/1/2W resistor in place of the one that blew,  and went thru the "Intitial start test" in the front of the manual, and found some of the functions don't work...  I started with the  resistance test, and according to the troubleshooting guide, RV1-RV4 (varistors) seem to be damaged,  possibly U1 also... So,, I guess this 40 year old meter could be repaired,  if I can get parts ...  At least the schematic, board layout and parts list is available... Other than for experience, its probably not worth it, tho....

[retiredcaps]

RV1-RV4 (varistors) seem to be damaged,  possibly U1 also

Use another meter to measure the resistance of RV1-RV4.  All of them should measure open circuit. You can make the measurements with RV1-RV4 in circuit. If one or more show a non open circuit reading, remove it and retest out of circuit.

When the fusible resistor is blown, it is not surprising that other input protection components go bad as well.

[retiredcaps]

You should also check RT1, the thermistor. It should measure around 1k ohm.

[knockbill]

Thanks for replying,,, at least 2 of the  varistors are bad, they have splits in them...  I'm game for trying to sort this out, until I reach a point where parts aren't available, or are cost prohibitive...

[knockbill]

Checked teh 4 varistors all read open,,, two are visibly cracked...
RT1 reads 900R...

[retiredcaps]

Checked teh 4 varistors all read open,,, two are visibly cracked...

Desolder all 4 varistors.  The meter will work without them, but you lose the input protection.  See if DCV and ohms works with the varistors removed.  If the meter works, you can get varistors from the usual places like mouser, digikey. 

I seem to recall a thread about someone replacing the varistors with disc ones and having a hard time fitting all 4 new ones in? I will have to search for that.

RT1 reads 900R...

RT1 is good despite reading a bit low.

[retiredcaps]

Found it.  Read post 6, 5, 4 and then 3 for it to make sense.  Drtaylor was on the original Fluke 8060A team.  Note his advice to replace all 4 varistors with matching ones.

https://www.eevblog.com/forum/profile/?area=showposts;u=99881

[retiredcaps]

Another thread regarding the varistors.  Here I suggested 5mm 430V ones from digikey.  44 cents each.

https://www.eevblog.com/forum/testgear/fluke-8020b-teardown-30yo-dmm-technology/25/