Re: 7L5 dot frequency reset bug - any clues or a fix?


Dave Casey
 

Cliff -

Did you see my response from December 8? I have a late 7L5 (> B090000) that
doesn't sound like it works any better than yours with respect to the reset
behavior.

Dave Casey

On Mon, Jan 20, 2020 at 12:19 AM Cliff Carrie <cliffcarrie@...>
wrote:

UPDATE:
The change of U830 (dot frequency counter) from PN 155-0117-00 to
155-0198-00 at 7L5 SN B060000 changes this part from a leadless ceramic
carrier to a leaded (DIP) ceramic carrier. I don't know yet if the reset
bug was fixed in the newer chip, Having recently acquired one of the later
155-0198-00 leaded chips, I wonder if it could be installed, temporarily
for a test or permanently in the leadless carrier socket without damaging
it. Pinout seems unchanged. I visualize a plastic backup block under the
chip between the two rows of pins to hold them against the leadless socket
contacts. I can easily create a pressure pad between the chip and the
adjacent circuit board to ensure it doesn't pop out of the socket.

Has anyone ever tried this (installing a DIP leaded chip) in any leadless
socket (not necessarily in a 7L5)?

I certainly don't want to replace the 40 pin socket for a test that may
show no change and/or some new incompatibility.

One more note: the serial number on a 7L5 does not tell the whole story
about the circuit level. Tek released at least 3 versions of a major update
kit 040-0872-xx. If your 7L5 has an added front panel "B - save A" lighted
pushbutton it is B070000 or higher or has this kit installed. Mine with
serial B03xxxx and the 040-0872-01 kit is equivalent to at least SN
B081400. Two boards (Storage and Digital Averaging) were also replaced with
a single board. Note that there are other serial numbers where boards
changed part numbers, but auditing my 7L5 against the manual, there don't
seem to be any circuit changes or improvements not covered in the update
kit.

Cliff Carrie



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