Fluke 724 Diode testing

[kleblanc]

I am looking for some help troubleshoot a Fluke 724 board where the left 4 jacks are not functioning.  The only thing I can think of is someone tried to measure >30 VDC to those jacks.  I tried testing the diodes and have numbers all over the place.  I was hoping someone could give me insight or tell me I'm insane to try fixing this.

I am attaching 2 pictures of the board, one whole board and the other I highlighted the diodes.

I am using a Fluke 189 meter and have not removed any from the circuit

- is the the meter
Black is the Diode on the board

+ is the meter
Red is the  diode
Stripe is the diode

             -/Black         -/Red
           +/Red         +/Black
D20           0.572 Vdc      1.625 Vdc
              38.00 Kohm         2.415 Mohm

D8           0.606 Vdc      OL
              1.766 Mohm       OL

D30 Left   0.657 Vdc      OL
              2.613 Mohm        OL

D30 Right   0.657 Vdc      OL
              2.659 Mohm         OL

D4 Left   0.687 Vdc      2.481 Vdc
              2.899 Mohm         7.06 Mohm

D4 Right   0.674 Vdc      3.17 Vdc
              2.874 Mohm         10.61 Mohm
         
   -/Black                -/Stripe
   +/Stripe                +/Black
D19   0.607 Vdc         0.597 Vdc
   27.00 Kohm         29.16 Kohm

D20   0.597 Vdc         0.606 Vdc
   29.11 Kohm         26.97 Kohm

[uncle_bob]

Hi

Those are back to back protection diodes or clamp diodes. They will measure goofy numbers in circuit. Troubleshooting a blown circuit often involves pulling stuff off to check it out of circuit.

Bob

[kleblanc]

Thank you uncle_bob. That would explain why nothing was making sense. I'm nowhere capable enough to try to remove smds to test and not destroy the board or components. Maybe 1 or 2, after that my chances of destruction increase greatly. 

I did some research and there is a company Test Point Inc in MD that will service these. The minimum charge is $150. Short money if the repair is less than $250 for a $2k meter new.

[uncle_bob]

Thank you uncle_bob. That would explain why nothing was making sense. I'm nowhere capable enough to try to remove smds to test and not destroy the board or components. Maybe 1 or 2, after that my chances of destruction increase greatly. 

I did some research and there is a company Test Point Inc in MD that will service these. The minimum charge is $150. Short money if the repair is less than $250 for a $2k meter new.

Hi

I'd check what a used one at auction (not buy it now) runs on eBay before I put a bunch of money into it. The ever popular eevBlog discount looks like it will get you some money knocked off the $2K at TEquipment.

Why check that number first?

It may take a bit of time to find an auction and get a price from it. Once you send the thing in, you likely will get a call that runs:

Ok, we've checked it out (= you owe us $150)
Repair involves replacing the xxxxx, that will be another $554.
Do you want us to ship it back (another $50 maybe) or fix it (maybe with free shipping)?

When the call comes in, you need to know what the "real value" is. They do not want to keep it on the shelf for a month or three while you make up your mind.

I've never done this with that particular outfit. It is how the conversation goes with roughly 100% of the gear I've sent in for professional repair over the last 10 years. ( = that's a mighty expensive thing you are replacing isn't it). I've spent enough time talking to these guys to understand that their margins are not all that high. The $554 charge might net them the same amount as the minimum bench charge. The rest goes to the cost of that board / part they had to swap out.

Bob

[kleblanc]

Thank you for experience. I should have been clearer in the min $150 repair charge. They state most estimates are "free" unless a rush repair. I don't work for free neither should they.

They are listed as A+ from the BBB with only 1 complaint that was resolved. The website states approx $185 to repair a 724.  I have never dealt with them before or heard of them.  I figured it's worth a shot, if all goes well then I might try a 743B with them. If it does not go well, I am out a busted 724 and will accept the consequences. I just might put a review out on Google of my experience either way.

I have dealt with manufacturers repair departments with the same experience you have had. It becomes cost effective to buy new with a calibration cert (and the infamous warranty fairy) for 25% more than the repair and cal.

eBay pricing goes for about $800 to $1000 for auctions. Plus the cost of recal. Unfortunately I don't trust an eBay calibration certificate included.  Proof maybe the unit functions yes, but I would still send it to a cal company of my personal preference.  If you can't trust/believe your equipment then you need to pay the cost to feel confident in it.

I perform field calibrations for the biotech industry, big difference than electronic calibrations. My experience is more to process controls and diagnostics, not down to the component level unless it's obvious.

[uncle_bob]

Hi

I'm by no means bashing the repair guys. They have very little control over what this or that part costs. Even the factory "one price fits all repairs" approach it not that bad when I see what they have swapped out. (When I break something it's *BROKE*)

If this is a piece of gear you use for work (and not a hobby item) then the decision is pretty easy. Get it repaired and get it properly calibrated. Pay somebody you trust to recalibrate it to your standards (do you need NIST and at what level?). You have a pretty good feel for what they go for. Whatever they come back with, you can make a decision then.

Bob

[kleblanc]

No problem Bob, I understand where you're coming from. It's the unknown of it all, the repair company, what is damaged, and the potential repair cost. I was just looking for some general feedback for the whole situation.  Sometimes it's nice to bounce an idea out there and see what others say.

This repair/diagnostics is above my level and I appreciate your input on telling me what exactly the diodes are for.  I would have wasted too much time tinkering and potentially doing more damage if you didn't help. The meter still measures volts,mA accurately, as well as measure/simulate thermocouples. It just can't source or measure ohms. So it's not a lost cause (yet).  If everything was bad, I would of cut my losses without thinking about getting it repaired.

LeBlanc

[uncle_bob]

Hi

Well there are certainly things that I should not attempt for fear of butchering a board as well. In this case, who ever it is that does the evaluation at the repair center will likely give you a better estimate on an un-touched board. The worst situation is generally when somebody else got half way in and gave up.

Given that most of the meter works, they may be able to give you a pretty accurate guess at the repair cost over the phone. If it's my money being spent, I always include a written description of the problem (and the not-problem) with the unit. My assumption is that I've done all I could to make sure the guy who looks at it knows at least what I do about the issue.

Bob

[kleblanc]

I agree 100%. I figured I'd give it a go myself and posted on the forum since there was nothing noticeable.  My guess was the diodes since I was getting all kinds of funky readings. But a little insight from you and I'd have to remove to properly test... My diagnosis is to send it to someone else!  Thanks again from preventing me "properly" diagnosing it (big hammer, little pieces, that's the problem with it!).

I did write a detailed description of the issues but basically no ohms source/measure and source volts dc is off.

I'll update the post once I hear what they say. Off to Staples now to ship it out.

[PA4TIM]

You have a 725 according the PCB.
I worked on both. They both had to much voltage on the inputs. There are two separate circuits. Often only one of the two is dead. The parts used are rather expensive.  I spended almost 80 euro for parts on the 724 and that was not enough because it still is dead. The owner decided to buy a new one. Maybe some day I finish it. I think I needs another 40 euro in parts for that.

[kleblanc]

The PCBs must be identical except for some different options. I am missing the 2 Relays on the bottom left.  There is another post on EEV showing a 725 tear down with these two relays and the serial connection on top.

Would you happen to remember what parts you changed and need to change? 

I have already shipped this off to the repair company. Once I get it back, hopefully repaired I will post an update.

[PA4TIM]

I made a mistake, I had a 725 and 726. The pcb's were  not the same. The 725 had a lot through hole parts. Both had also the Martel brand name on  the PCB.

I do not exactly remember the parts. I repair to much to remember details. Things I remember was a LT2051, LT1151, a cirrus ADC's, the FET switch, 2 Max 223, a few opamps. Thinking about it, things that made it expensive was that Farnell nor Mouser had all parts so I had twice the extra costs. From Mouser 20 euro because it was a to small order and Farnell because a part was from USA stock (25 euro extra)

The normal parts did a great job in protecting the movs, fuses and sparck gaps, 
because all protection stuff was still OK (But I think it should be the other way around).

[Nexis]

Did you manage to fix your 724?
Can you help me with the value of R114, this is the resistor which is between the left-hand side red terminals and R11.
Best regards
Neil

[kleblanc]

Unfortunately no, I sold it for parts. It seems that everything on the 72x series is difficult and not cost effective to repair.