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Percom Doubler / Model 1 Keyboard interconnect cable questions

B

Biff

Member
Joined
Jul 13, 2017
Messages
43
Location
NE Ohio
Hi,
Some time ago, I procured an older Expansion Interface and it had this plugged into the FDC socket.
I'm trying to figure out what doubler it is. I thought I read years ago that the early Percom units had pots like this one does.
Is this an early Percom Doubler? No identification on it except for "NEB" printed on the solder side.
I do find it somewhat odd that pin 22 "Test" had been lifted so it will not go into the socket.

While it may work fine (I haven't tested it) I swapped it out for one of Mav's reproduction doublers.

Also in the picture, is a Model 1 keyboard interconnect cable, seeing that I have never seen any factory ones that were not white with flat conductors,
I'm guessing that this is a mod? If so - it looks pretty professional to me.

IMG_8897.jpgIMG_8898.jpg

Jim
 
While I can't help you determine what Doubler it is......I know 100% that it is NOT an Aerocomp. I have one of the
Aerocomp in my Model 1.

Ian would be your best bet. He would probably recognize it from 20 feet away.

Larry
 
Funny how I've been at this for so long but every now and then someone turns up something that I've never seen before, and this doubler is no exception.

As best I can tell its a really early doubler with no data separation circuit, also the timing is set by potentiometers.

It would probably work but I would prefer the ones which came after this and had a proper data separator circuit.

Hope this helps,

Ian.
 
Al Hartman said:
That's some no-name doubler. The Percoms all had the Percom logo in metal on the board.

Mav's are undoubtedly better.
Click to expand...

Yep - I agree, which is why I retired this one for one of his.
I just ran across it again the other day while rooting around in my parts box. More importantly to me, is that keyboard cable on my Model 1 factory - or a mod? I never had this style of keyboard before - the one with the metal frame and attached keypad.

Jim
 
Biff said:
Yep - I agree, which is why I retired this one for one of his.
I just ran across it again the other day while rooting around in my parts box. More importantly to me, is that keyboard cable on my Model 1 factory - or a mod? I never had this style of keyboard before - the one with the metal frame and attached keypad.

Jim
Click to expand...

Its probably a mod someone made. Many folks would remove the original flat cable then clean out the mounting holes and insert IDE connectors. Then they would make a cable to attach to the connectors. This way if work was needed on either board a simple dis-connect and re-connect would make things a lot faster.
 
TRS-Ian said:
As best I can tell its a really early doubler with no data separation circuit, also the timing is set by potentiometers.

It would probably work but I would prefer the ones which came after this and had a proper data separator circuit.
Click to expand...

I think the situation may be the other way around: this is a very late-model doubler using the WDC 2791 (not 1791), which has highly reliable internal data separation and simple interfacing requirements. It’s like the 1773 chip on the model 4 gate-array board, but even more advanced, no longer requiring a high-speed 8 Mhz clock input.

http://www.bitsavers.org/components...1986_Storage_Management_Products_Handbook.pdf
 
Googling for "TRS-80" and "WD2791" I found an interesting detailed article from 1986 about a 2791-based Model I double-density board design. It's not the board you have, but, as the author said, "I have never seen an article on how to build a Doubler for the Model I in any computer magazines or newsletters, so even after all these years, this may still be a first."

"TRS-80 Model I and System 80 Single/Double Density 5 1/4" / 8" Adapter", by Maurice Abbott (Victoria, Australia), October 26, 1986, in Northern Bytes, Vol. 7, No. 5, pp. 14-19.
 
Thanks for jogging my memory Alan, I had actually spoken to Maurice a few times in the late 80s (he's a local... in that he was in the same city) and I was about to buy one of these doublers from him, but then a 2nd hand M1 system came along which had one in it. I remember saying to him that I would buy one in kit for and assemble it myself but he pointed out it needed a CRO to adjust the pre-comp which seemed like too much room for error for me.

It's mainly the reason why I went with the doubler design I sell now because it doesn't have pots which end users could inadvertently fiddle with and run into problems.

Cheers,

Ian.
 
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