DMM banana jack inputs

You might drop $17 for a set of ProbeMaster 8000 series leads

All gold-plated, soft silicone leads, lots of accessories available. Gorgeous.

Even if it turns out to be the meter that's broken, you'll be glad to have the leads for the next one!

Cheers

Phil Hobbs

Usually a break in the condutor. If + cross-section form of the male part then at least try generally cleaning male & female and insert razor blade forcibly each way in the + splits .

If the banana jacks really are intermittent, replacement are available: Judging by the number sold (247+105) it seems to be a common problem.

More Fluke parts, from Fluke: Now we know what usually breaks on a Fluke meter.

Hints:

1. Beware of new and improved.
2. That which is most difficult to replace, is usually the problem.
3. When all else has been replaced, that which remains, no matter how improbable, is the culprit.

The cheapest way to test this hypothesis is to get one of the free DMMs fro m Harbor Freight and use their leads on your Fluke. If this fixes the prob lem, you can confidently buy something of higher quality. Most banana jack s and plugs are interchangeable.

No whatever banana I stick in there is intermittent. (I use a lot of BNC to dual banana plug adapters.. then I can watch the fast stuff on the 'scope at the same time.)

GH

Thanks Jeff, looks like I'll be ordering one of those. (As you can see it's hard to get inside the plastic.)

George H.

Grin, for number three I had this circuit that was leaking ~1 Meg ohm, I couldn't figure it out, I'm ripping out everything. I finally pull out the toggle switch. Bingo! We had a box full of toggle switches of which ~10% had a resistance in the meg ohm region when 'open'. (Hmm that might count for #2 also.)

GH.

Then it is in the meter. You may be able to tighten up the contacts with a dental-pick, or you will have to take it apart and look for a broken solder joint or some such.

Peter Wieck Melrose Park, PA

Ah. Those put a lot of torque on the solder joints, of course.

Cheers

Phil Hobbs

Except that while replacing all that stuff, the real fault blew up several of the replacements, so it's quite possible to replace everything and still not fix it!

Cheers

Phil Hobbs

I agree with that but you're using a misleading singular.

THAT.......is THE problem.......... falsely implies only one thing is wrong. I've been fooled a number of times because two things were bad simultaneously. Sometimes one caused the other but sometimes it's just random.

In fact there is no theoretical limit to how many things can go wrong at once.

1. When everything has been replaced, and nothing remains to replace, it's time to give up.

I have a multiyear example of that happening to me. I am the not so proud owner of an IFR1500 service monitor. Over the years, the power supply had become more and more intermittent and refused to function on 117VAC input. However, the 12VDC input does work. In multiple attempts to fix the problem, I have systematically replaced every part in the switching power supply section except the magnetics at least 3 times. The last time, I replaced everything with all new parts before applying power. Something blew up anyway, so I gave up and have been running it on a 12VDC bench supply for about 5 years.

At one point, I even thought I had found the culprit: However, the celebration was premature. It died again in about a month.

My current strategy is to find a 117VAC +5V/+12V only "brick" power supply and replace the entire power supply. I can live without battery operation and DC power. However, I can't seem to find something suitable in a form factor that will fit. My latest scheme is separate +5V and +12V bricks, which hopefully will fit.

At least I'm in good company: "Also, many old IFRs are having power supply problems. If anyone would like to do an article on troubleshooting and repair we'd be happy to put it here."

The solder joints look fine... OK I just retouched them... same deal, (just as well cause I already spent $30 on the part Jeff linked to. :^)

When I replace it, I'll butcher the old one and see if I can find anything.

George H.

If the soldering is fine, then my best guess(tm) is that there's a broken spot weld or press fit connection between the pin that goes into the PCB, and the actual connection to the brass threads inside the banana jack. If I'm right, the pin might fall out when you unsolder it.

Umm... it's called an autopsy.

Banana jacks are so simple that, in the absence of obvious physical abuse, I find it hard to believe that it is intermittently faulty. I would try so ldering test leads directly to the lugs; when that does not fix the problem , I would look somewhere downstream like a crack in a pc board or a cold so lder joint.

I power a lot of prototypes from random laptop bricks with eBay SMPSes hung on them. The eBay units are generally quite okay as long as you derate their output current by about 3X.

Cheers

Phil Hobbs

I should add that you can make negative supplies out of an eBay buck regulator module by applying input power to +IN, grounding +OUT, and taking the negative output between there and the original common ground.

Cheers

Phil Hobbs

An old handkerchief pushed home with a small drill bit is one way to introduce some fluid and clean the inside surfaces.

..... Phil

No! I wiped 'em with IPA and a wooden cotton swab thing. I'm away from the lab for a while so I won't be able to try some other cleaner til I return.

George H.

Oh, sounds like you worked on the first NAP VCR switching power supplies! The parts dept finally came out with a repair kit, I think it contained 8 parts, and it was strongly suggested you replace all parts before applying power.

Mikek