Fluke 8050A OL all the time. - Page 1
Forum section: electronics / repair

author: Kryoclasm
author_rank: Regular Contributor
timestamp: August 04, 2017, 03:23:38 am
content: Hi, just thought I would see if anyone here has ever done a repair to an 8050A that is showing the +1 in all modes.Note: during the power on cycle, I do get zeros displayed, then they go away.New Note: This unit does not have a battery. Line voltage only.As I understand, +1 to the left side of the display is the OL indicator. In my testing, the comparator is sending the signal to the OL pin on the microprocessor in a periodic pulse.I don't visually see anything bad or leaking caps.One issue I did find, was my +13 volt rail onTP3TP2, if I remember correctly, was reading just over 11 volts. This seems too low, so I'm suspecting the filter caps because I'm getting just over +14 and -14 volts at the bridge rectifier.Could this be the main cause? I just don't want to have to pull all the caps and find I missed something.Any ideas would be helpful.Thanks.

author: retiredcaps
author_rank: Super Contributor
timestamp: August 04, 2017, 03:57:03 am
content: So just to confirm, if you plug in probes and measure a 1.5V AA cell, you get 0L? Same if you short the probes in DCV and ohms mode?

author: Kryoclasm
author_rank: Regular Contributor
timestamp: August 04, 2017, 04:13:08 am
content: Correct.Quote from: retiredcaps onTodayat 18:57:03

author: med6753
author_rank: Super Contributor
timestamp: August 04, 2017, 07:32:44 am
content: Quote from: Kryoclasm on August 04, 2017, 03:23:38 amGo after that first. My recently purchased 8050A had nearly +14 volts at TP3. You definitely have a power supply issue.

author: bd139
author_rank: Super Contributor
timestamp: August 04, 2017, 08:06:40 am
content: Every 8000 series Fluke I've had, which is quite a few, has had problems with filter caps leading to various bits of weird behaviour. Definitely worth replacing. If it's got the battery option, then things are more complicated so the thing may need modding or replacement NiCd's.

author: lowimpedance
author_rank: Super Contributor
timestamp: August 04, 2017, 09:37:38 am
content: Another easy thing to add would be to cycle through all the push button switches to help break up any contact oxidization if the unit has been sitting idle for any length of time.Does this change anything ?.

author: Kryoclasm
author_rank: Regular Contributor
timestamp: August 04, 2017, 07:07:51 pm
content: I will let you know what I find in the next few days.Thanks for the info.

author: ModemHead
author_rank: Frequent Contributor
timestamp: August 04, 2017, 08:14:13 pm
content: Checking caps and exercising the switches is always a good idea.Is this a battery or line-only model? They each have very different power supplies.I have several 8050As around here and as I recall, that power supply rail varies a lot, I think there's one working unit here that is as low as 10V on TP2 (TP3 is the +6V.) In fact, the printed copy of the manual I have (REV 1 8/80) actually labels that rail as +10V. The downloaded PDF (REV 2 7/84) labels it as +13V. It may depend on board revision.If the power supply ends up being OK, then you'll have to start going through it stage-by-stage. Maybe R2 is open. There's a troubleshooting chart in the manual, good place to start.

author: Kryoclasm
author_rank: Regular Contributor
timestamp: August 04, 2017, 10:26:46 pm
content: Just an update, this isnota battery unit and the 11 volts was on TP2. Ill have more info after work.I'm sorry, I dont know how the "not" got left off. I'm not trying to confuse anyone.

author: Kryoclasm
author_rank: Regular Contributor
timestamp: August 07, 2017, 09:45:33 pm
content: Found one bad cap!I ordered the electrolytic caps yesterday and I just pulled the old ones off the PCB.I dug out my trusty Mastech LCR tester. Either C12 or C13 was bad, both are 470uF -10/+75% 16V Caps.The good one tested solid at about 460uF, the bad one tested at 550uF then kept climbing till it went over 1000uF.Both these caps were connected to the 13V rail.I have a good feeling about the final outcome on this meter.

author: Kryoclasm
author_rank: Regular Contributor
timestamp: August 15, 2017, 04:25:47 pm
content: I have replaced all the power supply caps and Im now getting +15 volts on TP2.Also, I looked with my scope and the DC side is now smooth and filtered.Too bad im still having the same problem. I will now go through each stage, one by one.

author: Kryoclasm
author_rank: Regular Contributor
timestamp: August 16, 2017, 05:12:41 am
content: GOOD NEWS!I took another look at the meter while I am mostly awake and determined that I should put the switches in a position that I can get a valid test.I must have bumped them when I was soldering.She works!So, bad filter caps, easy fix. Thanks for those who chimed in with ideas.

author: bd139
author_rank: Super Contributor
timestamp: August 16, 2017, 06:53:48 am
content: Glad to hear. Congratulations