[volt-nuts] Fluke 732A pre-regulator revs

[Todd Micallef]

I wanted to pass on some information that may not have been previously
discussed.

I just finished working on a 732A with minor issues. I replaced the R10 and
R20 pots on the A3 board just like on my other 732A's along with the two
big caps C1 and C3. After performing the same battery charger procedure
that I used on the other three references, I could not get the charger to
go from CC mode to CV mode. I checked the output charge voltage and it
never reached the 31V necessary to change to CV. The manual I used was PN
645051.

I went through the board and found four carbon comp resistors out of
tolerance (R3,R6,R15-16), but they didn't seem to be causing my problem. I
changed them anyway and decided to use the procedure in the other 732A
manual PN788414.

The other procedure differs only by the setting of R20. Instead of setting
it to 33V, I set it to 28.2V.
I looked at the schematics and noted that Fluke made some subtle changes to
the design. R17 and R18 were changed to CR29 and CR30. The RT1 thermistor
was also removed. R19 was added through an errata/change. R16 changed from
10K to 100K.

The newer procedure worked fine and I could watch the charger voltage
increase to 31V and then drop to CV mode.

I looked through my other three references. One other had the newer design.
A second one was modified and RT1 was removed. There was an additional 15K
resistor in parallel with R19 near the card edge connector. I removed it
since this resistor does not exist in the newer design.

The last reference is of the older type and has worked fine with the older
procedure. I do not know if the newer procedure will work with the older
rev.

I have adjusted the other two A3 pcb's using the newer procedure and they
seem to be working fine. I noticed that one of the references was having
the same symptoms after a recent power outage. This may have been partially
the reason for some of my battery failures.

I hope this may be of help for those that may be having issues with the
battery charger.


Todd