#51 Fluke 8520A How far does this rabbit hole go Part1

In part 1of this video we tackle a few tantalum capacitors that has gone dead short. We also have to replace a faulty
LM340T-12 regulator after checking the voltage rails. Just how many problems does this "Working EBay Find" have?
I am at a stand still till I do more research...
Pics and discuss on my site:
gokarters.com/smf/index.php?to...
Fluke 8520A service manual:
assets.fluke.com/manuals/8520A...

[@linneypa]

I have recently managed to repair one of these units, with the aid of the service manual. My initial problems were in the Analogue Controller section - and with the aid of a cheap Logic IC tester - I found 6 bad TTL ICs and replaced them to get that section up and running. At that point I then had similar symptoms to this video - with the 'ERROR 01 HV' on Ohms and random and DC and AC voltages displayed. Since everything passes through the DC Buffer - I could prove that this was good, by measuring at it's output and then isolated the problem to the A/D convertor section. I eventually found this to be a bad LF351 Op-Amp and replacing this brought the instrument back to life.

[@TheRadioShop]

Alex, Thanks for sharing that. I am glad you were able to repair your unit. After finding many TTL IC's bad I put the unit down and never got back to it. Perhaps some time in the future I will give it another go.

[@MrCarlsonsLab]

Looking forward to part 2 Buddy! Great troubleshooting procedure, felt like I was doing it :^)

[@TheRadioShop]

+Mr Carlson's Lab Thanks Paul. I am going to try and get part 2 done this week. I want this puppy running. BTW, would have been fun watching you repair this thing. Man I hate logic debugging.

[@RestoreOldRadios]

Buddy - Great troubleshooting you shared. I really like and appreciate how you broke things down and isolated the trouble in each section. Best, Don

[@TheRadioShop]

+RestoreOldRadios Thank you Don. That's the fun part just going through a set and breaking stages down. Always happy to see you stop by. buddy

[@skeggjoldgunnr3167]

My $75 ebay Fluke 8520A had it's transformer pack shift on it's edge-card connector during shipping to me, shorting out and blowing fuse the instant I plugged it in. Having remedied that, I found "Error 14 ROM" show on the display at power-up. I remedied that by replacing corroded legs on ROM chips. Then, I found that my cheap Chinese 4-wire Kelvin leads were the reason that the unit would not zero on low-ohms. (The lead wires spin in the terminal plugs.) A great electrical cart meter now that services industrial automation controls in a machine shop. The bright red LED display is something I will always love.

[@TheRadioShop]

Thanks for sharing that. I really need to get back on mine but time has become hard to get by with here.

[@skeggjoldgunnr3167]

Your meter is not just worth $300 of work to get it going...($300 being the balance of The $400 value a 5.5 digit Fluke bench dmm that you bought for $100 - knowing what you'd get...) It is priceless, once made right. Those pretty red LED's do look the best. Solid, proven, tried, true and robust. Accurate and good looking. Serviceable. They don't make them like this any more. Please show your meter the love, attention and care that it deserves. My new Keithley 2001 (okay, not "NEW", ebay, $950- excellent condition) does not come with schematics. Such a thing a being able to service it yourself is unheard of these days.

[@skeggjoldgunnr3167]

It just occurred to me; I could sell you my ugly - yet working 8520A. I got $100 into it. + You pay shipping. I would do ebay / paypal. Put the two together and keep remains for parts? I even include a few spare fuses! I really don't need the thing any more. I've also got 5 new original power switches on order. (My pushbutton switch doesn't come all the way back out after pushing OFF sometimes...I cleaned and lubed switch internals and got it to come out on it's own every time now - albeit slow and weak...I have not opened it, I had no dielectric grease - only carbon-tet and wd-40.)

[@squirrelsrus1]

Looking forward to seeing what happens when the new caps are installed. I enjoyed watching your debugging process.

[@TheRadioShop]

+Bob Snyder Thanks Bob. I believe part 2 will bring fourth a lot of debugging lol. Those new caps cannot hurt for sure.

[@dirtydon8661]

I like this troubleshooting vid. I always learn from you. Looking forward to some more.

[@TheRadioShop]

+DirtyDon RC Thanks DirtyDon. Glad you get something out of them. More coming soon.

[@jaybats7865]

You’re amazing! I really enjoy your videos

[@larryk4mu240]

Also looking forward to part 2 Buddy! You make it look easy. I have 3 of the 8012A which look like your 8010s. They are still in good condition and are good old meters. I had never seen an 8520A. I can see why you wanted to get it going. Great video, waiting to see the follow up video. 73

[@TheRadioShop]

+Larry K4MU Thanks Larry. I think the 8012A is the European version? I remember reading about them Saturday. These seem to be nice little units. Just need the fuse holder for the 2 amp port. This is the first time I have had my hands on the 8520A myself. Easy? ah just a walk in the park lol. Thanks for the comment my friend.

[@TRXLab]

very nice video Buddy looking forward to part 2, Hope you are feeling better and will recover soon. All the best my friend. 73

[@TheRadioShop]

+TRXBench Hi Peter. Working on part 2 as I type. It may be a big one. Feel a bit better today. But my head is stuffed up. Thanks for commenting my friend.

[@normanthompson4729]

awesome troubleshooting had me all the way.

[@andypalm7061]

Interesting job. nice gear to! I have a Fluke 8050A that I replaced the display on back in the 90's. I still use it,and have the original case for it. i really prefer those LED displays in the lab; they just are so easy to read at a glance. I just have to see your next Vid on this.

[@TheRadioShop]

I love Fluke stuff, and Leds. I really need to get back on this unit. Perhaps soon.

[@WaterWhiteTuber]

I see you found the special factory option for carbon dating the meter. Most people dont know its hidden under that HV cover. LOL. As always, Awesome video :-)

[@GrandsonofKong]

Excellent debug procedure on those power supplies! From all I've heard those dip tantalum caps were a mixed blessing as time advanced on them in equipment. I have to agree with you on logic debug, especially when Proms and micro-controllers are in the mix.

[@TheRadioShop]

+GrandsonofKong Thanks for the nice words. You are correct on those tantalums. Great devices for tolerance and stability. But when they die it is a different story. Makes for nice fireworks when they explode in your face. Can really makes things nasty. Going to start looking at FET's tomorrow evening and see what is going on in the switching circuit. Thanks for stopping in :)

[@GrandsonofKong]

The Radio Shop I agree on those FETs/MOS-FETs and even the Op-Amps in that Buffer area. Several are wired to the +27V and if that went to +40V as you found, could have damaged them and latch the output to one rail...and that feeds to the ADC for Conversion. The displayed voltages when on VDC and ACV did drop after you fixed the regulator issues. Also somewhere is "logic" that says there is HV on the Ohms line when selected....probably near the ADC as well. Good luck...looking forward to the solution.

[@rick601a]

Those meters are nice while they work. But a nightmare after service support contracts end.

[@dennisqwertyuiop]

great job will follow along on this

[@TheRadioShop]

+DENNIS N Thanks Dennis.

[@mikesradiorepair]

Hmm, magic smoke has definitely escaped. A lot of people think I'm nuts because I replace tantalum caps when I do cap changes. I call it cheap insurance. Manufacturers seem to always rate them to close to operating voltage and I think that is what kills them so I usually double their voltage rating when I replace them. Mike

[@TheRadioShop]

+MikesRadioRepair Agree with that Mike. No not that you are nuts, meant about those tantalums.....Cheap insurance is a good rule with those things. Seen them blow a hole into a circuit board before. Thanks for the comment my friend. Waiting on your next video btw.

[@mikesradiorepair]

+The Radio Shop Yeah I have a pile of them to edit together and upload. Probably be after I get all the radios, test equipment and parts offloaded out of my box truck that I got at auction. Hit the gold mine of HV power supplies. Picked up 3 more HP 712B tube type high voltage power supplies. Makes for a total of 4 of them I have now.

[@TheRadioShop]

+MikesRadioRepair Great, was going to ask you how it went. Sounds like a nice haul. You need to go over to the site and upload some pics :)

[@MrMac5150]

Good troubleshooting.

[@TheRadioShop]

+MrMac5150 Thank you, More to follow.

[@g1fsh]

Hi Buddy hope u are well my friend? Nice job and great video so far you did a great job finding the issues on the positive voltage rails. I would suggest that u may be on the right track with replacing caos. It deffo cant hurt anyway..

[@TheRadioShop]

+Gary g1fsh Hi Gary. Feeling much better today thank you. I have allergies so there is always a sniffle here and there. What I liked about working on this unit is it was telling me the problems along the way. I rather replace those tants before they explode. Thanks Gary.

[@PapasDino]

I knew we were in for a rough ride when I saw "...rabbit hole"! I guess you can take solace in the fact the tantalum's did not fail catastrophically which really would be messy! Hang in there, I know you'll find the problem(s); good timing for you getting a four-wire machine same time Alan W2AEW did his latest video on that subject. 73 - Dino KL0S

[@TheRadioShop]

+Dino Papas LOL Dino. I knew that title would get some attention. When I started the unit and checking it out I started seeing a chain of problems. Was wondering just how far it will go. I think I am down to one problem now. But you never know when someone else has had a chance at it. I was pleased to see Alans video also. Thanks for stopping in as always. 73

[@Beretta96Dan]

Hi, Buddy. About the only help I could give you would be to tell you to sit it on top of the 940 with the dot problem. Lol! Save these to work on when you have some cold ones in the fridge!

[@TheRadioShop]

+Beretta96Dan LOL. Trust me, the fridge is stocked! Well, the Kenwood is full of design flaws. I think (hope) the Fluke is just tired from old components. And maybe it will come to life quickly. We will see. Thanks for posting my friend.

[@brucefriend3760]

I am restoring a Fluke 8120A DMM with Nixie tubes. Turned out the thing just needed cleaning, a set of new binding posts and the fuse holder replaced. Now my problem is finding 1/8 A SB fuses! I saw a couple of these for $50 OBO on Ebay and wondered about them. Having a 4 wire DMM would be nice.

[@TheRadioShop]

+Bruce Friend Hi Bruce. Amazing what a little cleaning can do. those 1/8 SB's are getting harder to come by also. $50 bucks eh?

[@vidasvv]

Great video Paul, thank you ! 73 N8AUM

[@TheRadioShop]

Thank you

[@ruhnet]

Good stuff! Thanks for sharing!

[@hermannschaefer4777]

Rule No 1 with old electronic: Get rid of all tantalum caps.. before turning on or anything.

[@TheRadioShop]

Well said!

[@StarGazer7373]

How about some of those op amps in the dc buffer circuit that had about 70V put across them when the 27V went to 40V? U210, U211. Are they fried? The DC Buffer supplies the measurement signal to the ADC input. If it is no longer buffering correctly, the ADC will measure voltage when none is present. I suspect the Error 01 is because the unit thinks it is detecting voltage on the inputs, and you can't measure ohms with a voltage input, so it refuses to go into that mode. When you pull the dc buffer jumper plug out, the output of the buffer goes to 0V, and the ADC reads 0, so it thinks it is ok then to go into ohms mode, and no error 01. See if the high voltage blew something. There is voltage going out to A/D input that shouldn't be there when the buffer input is 0V.

[@TheRadioShop]

Impressive!. This was my thoughts also. Specially when I pulled the jumper out and saw the error went away. Good troubleshooting my friend. I do think you hit the nail on the head. Will get back to this one in a few weeks. So many things going on in the shop and at work. Thanks for you input.

[@billmoran3812]

StarGazer7373 I agree. I think when the 27V rail went high, it took out one or more chips on that buffer board. Anything that gives the ADC a signal that voltage is present is the culprit. Could be tough to locate.

[@1903A3shooter]

Well that was fun. OK for me it was fun.

[@TheRadioShop]

Thanks, I am glad it was fun

[@yago1467]

Good stuff Buddy. Just trying to catch up with vids, I lost my YT account again! Lordy I am hopeless of late! :P

[@TheRadioShop]

+Yago LOL, again mate? You better engrave that on the wall or get it tattooed on you arm :) Always good to see you stop in.

[@rickgunther7328]

i have the same multmeter in storage . I think i will pull it out and go throuht it again it has the same problems this is why i watch your videos ricks radio shop.

[@TheRadioShop]

+Rick Gunther Thanks Rick. Yes pull it out and get started on it. Do you remember what it was doing when the error occurred? That could help in troubleshooting. Thanks for watching.

[@Partsocaster]

So what happened? I can't find part 2. Great job so far.

[@TheRadioShop]

Still working on it. Taking care of the customers stuff is a first. I did get all the caps changed out and now troubleshooting it.

[@Partsocaster]

+The Radio Shop Understand that completely. Thanks for the reply!

[@firozsunderji6940]

Hi i bought this meter 6 months ago, FLUKE 8520A Meter is working fine, but i cant get zero on the display in ohms when i touch 2 probes together can you help thanks.

[@davidhaney1394]

R256 is the one thats blown ...

[@shana_dmr]

Sadly it's typical to find these mA fuse holders missing as they contain 10$ HRC fuses inside so resellers will usually "borrow" expensive fuses and throw holders in junk bin.

[@TheRadioShop]

Agreed. Funny I have not been able to find replacements. Good thing I have a few dozen more meters to use.

[@danielgoldman677]

the second part is in the parallel universe ...

[@bekiil]

The diode looks cracked. Noticed it? Labeled cr215? kzbin.info/www/bejne/i320o6KNf7qNmtkm7s

[@danieljohnson8437]

Radio