Hi Folks,
I've posted some quick pics of the Priam DataTower here:
http://www.flickr.com/gp/114907644_at_N04/U9htba
After the struggle to accept the fact that these things actually
exist, there were 3 challenges with this unit:
- There was no interface cable to connect the DataTower to the Lisa.
Disassembling the EPROM and reverse engineering the Lisa interface
card, reviewing the documentation (many thanks to BitSavers) for
various Priam controllers, and examining the driver/receiver
combinations at the two ends resulted in a probable cable pinout,
which seems to work.
- Once it was able to communicate, the controller was reporting that
the RAM self-test failed. The controller uses an 8088 family
microprocessor, so it was possible to trace the self-test with a
logic analyzer to observe the point of failure. The problem turned
out to be that when writing to the RAM, the write signal remained
asserted well after the address lines were no longer valid, and so
unintentional changes were being made to semi-random RAM locations.
In this state it could never have passed the self-test, yet the
controller appears fully operational aside from this write timing
problem. As it is unknown as to whether this controller ever worked,
only a minor attempt was made to determine if some component had
failed in a way that produced this subtle change. Instead, a
modification was made to properly terminate the RAM's write signal
while the address is still valid.
- Once the controller was able to pass the self-test, the drive
would unlock and spin up, but then time out. After studying
schematics and theory of operation for other Priam drives, and
substantial hours of troubleshooting, it was determined that two
parts had failed on the servo board. The parts were IH5052 analog
switches (similar to the 4066 and apparently the only CMOS parts in
the unit, which are much more fragile than TTL parts). After
replacing these with currently available equivalents, the drive
operates correctly.
It remains to be seen whether the tape drive is able to read/write
properly, but it does rewind and re-tension on demand. A large part
of the challenge here is fixing up DC-600A tapes so that they spool
properly again.
James
PS. For those of you with any uncommon Twiggy floppy disks, please
back them up before they deteriorate further! If you have working
Twiggy drives, you can use BLU to do this; feel free to ask for help.
If you don't have working Twiggy drives, there are a few people who
have a working Lisa 1 that will be happy to assist. If you are a
collector, consider that a rare or one-of-a-kind original disk is not
going to be worth so much if it is just a label on an unreadable disk
and no-one can find the software it represents.