[Techtoolslist] Recommend add a fuse upgrade for Fluke 9100 series

[John Robertson]

On 2018/08/19 10:29 PM, Ian Eure wrote:
> John Robertson writes:
>
>> I am now on the hunt for the small switching transformer on one of my
>> 9100s as the original was cooked. Unfortunately it was not fused by
>> Fluke and I am not sure where I am going to find this sucker. It is T1
>> and is called Transformer, Converter 775932 (manufacturers #89536) in
>> parts listing.
>>
> 89536 is the manufacturer code for Fluke.  Many parts in the 9100A
> service manual are listed this way, even if Fluke wasn’t the actual
> manufacturer.
>
>
>> Shy (@ Navatek) hasn't seen one before but is still checking...
>>
>> This is a multi-winding sucker and provides the isolated voltages for
>> the serial ports as well as the 70V for the display. Years ago I had a
>> secondary cap (C101) short on this transformer and it let the magic
>> smoke out. I had set it aside and forgotten, but now I am restoring a
>> few 9100s and dug this out and found the smoked Xformer.
>>
>> In the meantime I have modified all my 9100s lifting the furthest leg of
>> inductor L2 (10uH) away from the power connector J15 and then add a GMA
>> fuse holder in series from raised leg and the PCB. I find a 300ma fuse
>> works just fine. Which is interesting as Fluke put a 1A fuse in the 70V
>> output to the display...obviously overkill!
>>
> The fuse on the 70V line is supposed to be .125A, not 1A.   Maybe the
> original popped and someone put the 1A part in, and that’s why your
> transformer is wrecked.
>
>    -- Ian
>
It wasn't a 70VDC line issue, rather tantalum capacitor C101 shorted 
out, taking the Xformer as that cap was on the -12VDC output...hence my 
recommendation to add a 300MA fuse to the Xformer input at L2.

Tantalums have a bad habit of shorting... Check schematics in Service 
manual, page 7-5 9100A-1001 (3 of 4), there are several that would take 
the Xformer if/when they short out.

Thanks for the reminder about the 0.125A fuse for the display, I should 
have noticed that as it is clearly labeled on the schematic.

John :-#)#

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