TRS-80 Model 1 Expansion Interface question?

[ben]

On 3/20/2017 9:43 PM, Fred Cisin via cctech wrote:
> On Mon, 20 Mar 2017, Win Heagy via cctech wrote:
>> But, the FD1771 IC, for some reason, was removed from an otherwise
>> apparently functional EI.
>> http://imgur.com/a/3NzOh
>> Is there any reason why this chip would be removed?  I see a number of
>> them
>> on ebay for around $25.  The expansion interface hardware manual
>> indicates
>> it is an FD1771B-01, but the service manual indicates a couple
>> possibilities....FD1771 A/B -01 -11.  Any considerations to look for
>> here?
>
>
> Some owners replaced the 1771 with a daughterboard that contained a 1771
> plus a better data separation circuit.  The 1771 included internal data
> separation, which WD advised not to use.
> "EVERYBODY" used one of those.
> Before selling the Expansion Interface, the previous owner might have
> removed the data separator and sold it separately.
>
> Some owners replaced the 1771 with a daughterboard that contained a 1771
> plus a 179x, called a "Doubler".  That added double density (MFM)
> support. The Doubler included a 1771 because the 179x was incapable of
> writing some of the address marks that Model 1 TRSDOS used in its disk
> format.
> "EVERYBODY" used one of those.
> Before selling the Expansion Interface, the previous owner might have
> removed the Doubler and sold it separately.
>
> Both the Data Separator and the Doubler COULD HAVE used the 1771 that
> was taken out, but usually came with one already installed.
> 1) it made for one less prying out, bending pins and reinstalling with
> bent pins or backwards
> 2) it meant that there was a known good chip going in.
>
>
> Some owners replaced the 1771 with an aftermarket daughterboard that
> contained a 1771 plus some circuitry to do 8" SSSD.  Often that was
> accompanied by a sandwich board for the Z80 in the CPU to remap memory
> for CP/M, and a CP/M for it.
> (such as Parasitic Engineering, and Omikron Mapper)
> "not EVERYBODY" used one of those.
> Before selling the Expansion Interface, the previous owner might have
> removed the adapter and sold it separately.
> (There also existed a "remapped" CP/M for the TRS80 that would work
> without the hardware remapping, although in general no known commercial
> software worked with that setup.)
>
>
>
> In addition to the 1771, does your Expansion Interface include the
> "RS232 board"?  A Radio Shack Computer Store manager asserted that any
> incompatabilities with the standard were legitimate, "because OUR RS-232
> board is RADIO SHACK 232"
> Before selling the Expansion Interface, the previous owner might have
> removed the adapter and sold it separately.
>
>
> There were a few modifications to the EI over time.
> The first version had a simple straight through cable.
> Then they made some changes and switched to a cable with a circuit box
> in the middle of it.
> Then they made some changes and switched to a cable with a circuit box
> in the middle of it, plus a small second cable.
> Then they made some changes and switched to a simple straight through
> cable.
> Make sure that you use the appropriate cable(s) for the level of changes
> that were made to yours.
>
> To keep reliability, do not plug/unplug and move the CPU and the EI.
> If you are going to do so, then bolt both pieces to a piece of plywood.
> RIV-NUTS or NUTSERTS into holes drilled into the bottom of the EI and CPU.
>
>
> You did not HAVE TO put the power supply for the CPU into the
> compartment in the EI.  If you do, cutting a notch in the case means
> that you can tuck the excess cord in there to have 3" of power cord
> between the EI and CPU, instead of a couple of feet going out the BACK
> and around to the front.
>
>
> The RCA TV set that Radio Shack used as a monitor had a great big empty
> space where the tuner used to be.  Plenty of room for a disk drive, or a
> pair of half-height drives.  Mu-metal surround was kinda important.
>
> The CPU needed a trivial modification to add lower-case.  Often
> accompanied by adding a "Control key", and sometimes a mod to give
> reverse video.  Remember to put glyptol on the screw after making
> modifications, since warranty was void if there wasn't any glyptol.

Act quick before Radio Shack closes its doors forever.

>
> --
> Grumpy Ol' Fred             cisin at xenosoft.com
>
Ben.
What happens to my life tube replacement guarantee now?