Fluke 732a repair

[Bill158]

Can you tell me more about the blinking LED at low power?
[/quote]

I have 6 of  these F732A units and I have never see the "IN CAL" led blink.  There is no circuitry in there to allow this to happen.  The "IN CAL" led is latched on by shorting the LO to the RESET point.  If the battery voltage drops below around 22 volts then the latch shuts off and the led cannot be turned on until you do the RESET.  I set my "float" voltage across the batteries to be about 27.3 volts, as best as I can.  BUT you have to wait for at least 24 hours after installing new batteries so that they can " top out" and get their full charge.  I also set my trip point from constant current (charging) to constant voltage (floating) of the charging circuit to be 29.2 volts.  This adjustment is very difficult to obtain accurately.  So I just try to get it as close as possible, usually between 28.7 to 29.5 volts.  But again this is with a battery pack that has been at constant voltage float for at least 24 hours.  If you set the trip point to 31 volts there is a good chance that it will NEVER trip over from constant current to constant voltage and you will FRY the new batteries!  DON'T USE THE PROCEDURE IN THE MANUAL TO SET THE TRIP POINT!  It doesn't work.  I just watch a DMM closely, pull the 732A AC power plug, plug it in again and try to capture the trip point visually, but the DMM I use has a MAX statistics math function so I just set the PLCs to 1 and then let the math do the job for me.  The charging circuit will NOT go into constant current if you have pulled the battery pack and and then reinserted it.  You then have to pull the AC power plug and then insert it to get into constant current mode.
I have one 732A where the 1.018 or 1 volt output is not correctable because the adjustment is out of range.  I just don't worry about this because the 10 volt output is the critical one and that is the one you want to use.  Going into the oven assembly is just NOT recommended unless you absolutely have to fix something!  You are dealing with ribbon cables which can break off from the PC Board easily.  I would sure stay away from that.  I have gone into one to fix a problem, but I was VERY CAREFUL about what I was doing.  If you need either of the lower voltage outputs use a Kelvin-Varley divider, F720A or equivalent, to get those voltages. 
Bill

[TheSteve]

The 732B will flash the "low bat" LED, I've never seen any flashing from a 732A.

[MegaVolt]

I have 6 of  these F732A units and I have never see the "IN CAL" led blink.  There is no circuitry in there to allow this to happen.

Thank you for confirming. I seem to have mixed up with 732B

[MegaVolt]

But no .... here is a quote from the instructions:

[Bill158]

But no .... here is a quote from the instructions:

My bad for thinking we were discussing the "IN CAL" LED.  Now I see that we are discussing the "BTRY CHG" LED.
How interesting.  This paragraph comes from the "Acceptance Test" section 4-30 after doing repairs.  Since all of my 732As were used and many did not even have batteries installed or completely dead with no chance of being charged I never read that section.  I always just began by installing new batteries before even trying to power up the 732A. Once new batteries are installed the "BTRY CHG" LED will come on, after the battery switch is set to "ON" and then the AC power is removed and then connected.  Then the CI/CV circuit will be in the CI state until the battery voltage reaches 29 volts (if the circuit was correctly adjusted in the past) and then go into the CV state.  This paragraph (4-30 1c) makes no sense because once the CI state starts the batteries will be charging for a while IF they were low in the first place.  About the only time I can imagine where this would happen is if the batteries have gone bad and won't hold a charge because one cell or more cells have a high impedance.  Then the voltage across the batteries would go up to the trip point rapidly where the supply would switch over to CV.  But then the CV mode would be enough to keep the pack at 27.2 volts.  This doesn't explain why the LED would blink.  But I have also seen where the battery pack cannot ever reach the CI to CV switch voltage, because one or more cells have an internal short, and it stays in the CI mode and then fries the remaining batteries, the whole pack becomes too hot to touch and batteries begin to swell and then burst and spill their contents all over the place.  I have had this happen more than once with batteries that had passed the monthly check (paragraph 2-47).  Bottom line here is why did FLUKE think the blinking could happen?  I can't imagine a situation that would cause this in a AC power state.  I am wide open to an explanation.
Bill

[MegaVolt]

I watched the standby voltage on the battery and found a direct temperature dependence.
Although the theory claims that the dependence should be the opposite.
What am I wrong about?
I looked at the circuit and it was designed just like that. Did older batteries require a direct dependency? And the new inverse dependency?
Can this be easily fixed?

[czgut]

In My 732A 1 V also drifted +25 ppm out of nominal value. In my case it seems to drift continuously about +6ppm/8years.
From my measurements it seems, that resistance of 9kOhm Resistor in 1V divider (9kOm + 1kOm) is drifting about -1 ppm/y . 1 kOhm seems to be stable to <2ppm/8years.

[leighcorrigall]

Excuse me for hijacking this dated thread.

Given that the Fluke 732A and 752A share the same enclosure and feet, I decided to replicate the voltage standard feet so that I could produce them for my voltage divider.

Attached is a CAD file for the purpose of 3D printing feet for either unit. They have been printed with a Figure 4 by 3D Systems and tested. Note that the foot replicate is not an exact match because I got tired of dealing with the draft angles on every conceivable surface. They will be suitable replacements regardless. Draft angles are only necessary for plastic injection moulding and serve no purpose for additive manufacturing, to which more members will have access.

I hope this is of use to our community. Please feel free to contact me if there are changes and suggestions to the existing design that you would like to share.

https://xdevs.com/leigh/fluke_7X2A_-_parts/MP18/

Enjoy.

[leighcorrigall]

Does anyone know what the oven insulation foam in made of? I would like to try and replace it in a damaged enclosure. The material is extremely brittle and falling apart.

[doktor pyta]

It looks like two compound rigid polyurethane foam.
I once used this type for thermal insulation: 'EKO PRODUR PM 4032'.

[leighcorrigall]

Attached is a reverse engineering STP file of an insulated anchor found throughout the Fluke 732A and perhaps other Fluke equipment. For example, it isolates parts of the battery module from the rest of the chassis (pictures for reference). I noticed that a lot of them break due to aging! Note that I have not yet printed these parts. I may share additional details depending on the results.

Please let me know if any updates are required so I can upload the next revision here. Thank you.



Enjoy!

[leighcorrigall]

The 732A foam can degrade if the environment is harsh. One of them in my possession was exposed to high humidity for a long time during operation. Not a good combination.

I have reverse-engineered the foam for the ovenized assembly. In my case, I had IKO Enerfoil Sheathing (polyisocyanurate foam) cut with a bandsaw, according to the attached draft. I did not go with the original shelves to assemble the walls. Instead, I applied a simple approach to installing the front and back walls and sides inside the case quickly. The bottom and top are the final parts to assemble. If one wants to, one can take my draft dimensions and redesign how the walls interface.