Fluke 8020A blown fusible resistor... - Page 1
Forum section: electronics / testgear

author: knockbill
author_rank: Regular Contributor
timestamp: June 25, 2016, 12:55:09 am
content: 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.pdfRegards,John

author: Excavatoree
author_rank: Frequent Contributor
timestamp: June 25, 2016, 01:30:20 am
content: 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.

author: Excavatoree
author_rank: Frequent Contributor
timestamp: June 25, 2016, 01:34:13 am
content: I found an 8020A in my "working" pile. Resistors are as you describe.

author: knockbill
author_rank: Regular Contributor
timestamp: June 25, 2016, 01:37:17 am
content: Thanks,,,I didn't notice I posted the wrong manual... Is this resistor a Fluke part, or can i get it from Mouser?

author: Excavatoree
author_rank: Frequent Contributor
timestamp: June 25, 2016, 01:48:16 am
content: 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 percentR2 1K 2 watt 10 percentI 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.

author: knockbill
author_rank: Regular Contributor
timestamp: June 25, 2016, 02:37:54 am
content: 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...

author: retiredcaps
author_rank: Super Contributor
timestamp: June 25, 2016, 05:30:32 am
content: Quote from: knockbill on June 25, 2016, 12:55:09 am@OP, how high was the ACV that killed the 8020A? 1500V? 2000V?The correct manual for the 8020A ishttp://exodus.poly.edu/~kurt/manuals/manuals/Fluke/FLUKE%208020A%20Instruction.pdfThe all important errata manual is athttp://assets.fluke.com/manuals/8020a___imeng0003.pdfwith 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 athttp://mrmodemhead.com/blog/fluke-87-fusible-resistor/

author: retiredcaps
author_rank: Super Contributor
timestamp: June 25, 2016, 05:34:37 am
content: Quote from: knockbill on June 25, 2016, 12:55:09 amFor 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 lessuntil you get the proper fusible resistor.

author: retiredcaps
author_rank: Super Contributor
timestamp: June 25, 2016, 05:52:24 am
content: Quote from: knockbill on June 25, 2016, 12:55:09 amYou 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.

author: knockbill
author_rank: Regular Contributor
timestamp: June 25, 2016, 10:52:19 am
content: 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 ?

author: Excavatoree
author_rank: Frequent Contributor
timestamp: June 25, 2016, 12:46:49 pm
content: 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.

author: retiredcaps
author_rank: Super Contributor
timestamp: June 25, 2016, 01:22:40 pm
content: Quote from: knockbill on June 25, 2016, 10:52:19 amAs 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

author: ModemHead
author_rank: Frequent Contributor
timestamp: June 25, 2016, 01:25:23 pm
content: Quote from: Excavatoree on June 25, 2016, 12:46:49 pmThe 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.

author: retiredcaps
author_rank: Super Contributor
timestamp: June 25, 2016, 01:29:42 pm
content: Quote from: Excavatoree on June 25, 2016, 12:46:49 pmThe 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.

author: knockbill
author_rank: Regular Contributor
timestamp: June 25, 2016, 02:29:37 pm
content: 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...

author: ModemHead
author_rank: Frequent Contributor
timestamp: June 25, 2016, 05:35:27 pm
content: Quote from: knockbill on June 25, 2016, 02:29:37 pmI 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.

author: knockbill
author_rank: Regular Contributor
timestamp: June 25, 2016, 05:52:47 pm
content: Thanks,,, that's more reasonable...

author: knockbill
author_rank: Regular Contributor
timestamp: June 26, 2016, 06:15:18 pm
content: 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....

author: retiredcaps
author_rank: Super Contributor
timestamp: June 26, 2016, 06:45:41 pm
content: Quote from: knockbill on June 26, 2016, 06:15:18 pmUse 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.

author: retiredcaps
author_rank: Super Contributor
timestamp: June 26, 2016, 07:39:06 pm
content: You should also check RT1, the thermistor. It should measure around 1k ohm.

author: knockbill
author_rank: Regular Contributor
timestamp: June 26, 2016, 11:03:13 pm
content: 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...

author: knockbill
author_rank: Regular Contributor
timestamp: June 26, 2016, 11:15:32 pm
content: Checked teh 4 varistors all read open,,, two are visibly cracked...RT1 reads 900R...

author: retiredcaps
author_rank: Super Contributor
timestamp: June 27, 2016, 03:25:54 pm
content: Quote from: knockbill on June 26, 2016, 11:15:32 pmDesolder 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.QuoteRT1 is good despite reading a bit low.

author: retiredcaps
author_rank: Super Contributor
timestamp: June 27, 2016, 03:34:03 pm
content: 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

author: retiredcaps
author_rank: Super Contributor
timestamp: June 27, 2016, 05:32:15 pm
content: 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/

author: knockbill
author_rank: Regular Contributor
timestamp: June 27, 2016, 05:33:33 pm
content: I already lifted one end of the varistors and used a 1k/1/2W to close the fuse... did a check of the resistance range from 20M down to 100R, and its almost dead on... I'm thinking I may cut my losses and use this meter for a dedicated ohms checker, as I don't have anything else that reads over 2M, and as accurately as this...Seems any source that has both the varistors and the resistor/fuse has to drop ship one of them, so the shipping costs will be out of budget, for cheap parts like these... In the mean time I can button up the meter, and use it for ohms, with out exposing it to any Current or Voltage without protection.......Thanks for helping me get it sorted out, if I run into a deal on the parts, I'll re visit it...

author: retiredcaps
author_rank: Super Contributor
timestamp: June 27, 2016, 05:55:33 pm
content: Didn't know there was a parallel discussion over athttp://audiokarma.org/forums/index.php?threads/fluke-8020a-blown-fusible-resistor.722020/

author: knockbill
author_rank: Regular Contributor
timestamp: June 27, 2016, 06:07:29 pm
content: Yep,, the Tube Forum is where I mainly post, but they don't have a dedicated test equipment forum...