Funky Fluke 87-iii revision

[ogdento]

Yesterday I ran across a post describing a burned 87-iii main/U4 IC, and what was strange is that the board had a different U4 IC number - and just looked different - than any 87-iii board I'd ever seen... but it is absolutely an 87-iii meter.  (if you're interested, the post is: https://www.eevblog.com/forum/repair/fluke-87-iii-burned-processor/)

Of the 10 or so 87-iii boards I've seen they've all had gold plating, almost exclusively used smd components... and had a U4 IC marking of SMX2-87, but this guy's 87-iii has an IC with 921606, which sounded familiar.  I looked at a couple of my old 87-i parts boards and they've got 921606 chips on them! 

(I always thought the 87-iii had a new IC because of the new logic and other stuff that was added... so I wondered if the 921606 IC is the SAME as an SMX87-2.  This would be great for anyone who's got an 87-iii with dead U4)

Anyway, a broken 87-iii I just won on eBay arrived today, and when I cracked it open it had the same weird 87-iii board and U4 chip!!


Here's the back... definitely an 87-iii:


I realize this must be the first revision of the 87-iii, notice that it looks very similar to the CAT-3 rated 87-i (aka 87-ii)... uses the old regulator, selector switch, capacitors, green backlight, etc.  But it's got all the new 87-iii 74HC logic chips on the back, and the extra stuff on the front.

Does anybody know for sure if the 921606 chip is the same as the SMX2-87?

[ogdento]

Here's the shot of a CAT-3 rated 87-i, aka 87-2 (left), the older 87-iii board I got today (center), and the 87-iii board I'm used to seeing (right):

[mzacharias]

I don't see any date codes on that processor on the right side one, but I notice a newer style function switch (cheaper) which obviously would use the circuit board tracks similar to an 87-5.

Very peculiar.

[ogdento]

Hey mzacharias,

Yeah so for that 87-iii SMX2-87 chip all the way to the right, I figured the date code might be the "0039" number?  Maybe the 39th week of 2000?

Anyway, I'm wondering if that SMX2-87 chip is the same as the 921606 on the other two meters - the 87-iii in the center and the Cat-3 87-i (87-ii) on the left.

[bluey]

Fluke service manual rev 5 1996 says they are the same.

[ogdento]

hey thanks bluey,
i always assumed the smx2 was a new chip... didn't think to look for it in the 87-i manuals!!