ET-3400 Revision Questions

From: Lawrence Walker <lgwalker_at_mts.net>
Date: Thu Oct 24 21:54:57 2002

 Can't be of much help cause my model is the same as on your schematics.
with the extra 2112s. I do have the Heathkit Lab manuals that we used the
3400 to train on. They were available from Heathkit at last check (some time
ago).

Lawrence

> Guys,
>
> I just got an ET-3400 that was partially built. On average, the
> construction seems to be fairly good. I haven't yet plugged the rascal in, I'm
> still doing a visual checkout and comparison to instructions and schematics, and
> trying to find the point or points at which the kit has remaining steps.
> Mechanically it seems to be in great shape: the labels for the case haven't been
> applied, and the case is completely unscratched. Soldering is generally good,
> but flux hasn't been removed so it looks untidy. The keys still have the thin
> plastic film over their caps, and it's obvious that this unit has had little if
> any use. Perhaps the builder had a problem and wasn't able to diagnose it, I
> don't know.
>
> I have a manual with schematics, but it's apparent from inspection that the
> manual refers to an older revision (part numbers different, parts changed or
> absent, etc.). The main board is part number 85-2712 (-2). Unfortunately, I
> don't have the x-ray views of the board, and the component side is completely
> covered with a white plastic mask that carries various labels and graphics, so
> traces on that side are all but invisible.
>
> Before I break out the probe, I've got a couple of questions, for those who may
> know:
>
> The 6800 in the schematic is a 6802 on the live unit, and the 6875 in the
> schematic is absent altogether, and there's no trace (no pun intended) of a
> location for it. This seems to make sense; the '02 has its clock generator on
> board, correct? Where is its 128 bytes of RAM mapped? There are also two
> 2114's on this board, rather than two 2112's and two empty sockets for
> additional 2112's.
>
> There's a jumper soldered between U4 (a 74126) pin 5 and the nearest
> resistor (part of the 8-LED assembly). Not on the schematic, but it seems
> like it quite possibly could be a pull up or down (pin 5 is an input to a
> tri-state buffer, pin 6 is the output to the DBE signal on the MPU, at
> least, according to the schematic I _have_). Again, I can't tell easily in this
> area of the board because the component-side traces are covered with the white
> plastic mask.
>
> The ROM is 444-364, so I suspect the source listing in the manual I have
> (for ROM part number 444-17) won't nearly cut it and routines have probably
> moved. Does anyone have a listing of this ROM they'd be willing to share?
>
> IC1 is listed as a 'LS241 on the schematics I have, but there's a 'LS240 in the
> socket. I can't visually verify that the change is appropriate, or just a bad
> substitution by the builder, because the component-side traces are covered by
> that white mask. It seems plausible that Heath would, for whatever reason,
> decide to invert the sense of the lines buffering the eight binary display LEDs
> (not the 7-seg displays on the right, the eight FLV117s on the left), and this
> would be an appropriate substitution. Of course I can quickly find out with a
> logic probe or some of Heathkit's infamous "short wires", but I was just
> wondering if anybody knew for sure?
>
> Does anyone have a GIF or JPG (or other format) of the x-ray of the main
> board (even a newer or older revision), or a copy of the "Illustration
> Booklet" that they'd be willing to share? For that matter, does anyone have a
> copy of the manual for this (or near) board revision? The manual I have is from
> Raymond Sarrio, and it was listed on his site as the Illustration Book, but it
> turned out to the Manual (I'm going to contact him as well). I'm happy to
> buy/trade...
>
> Thanks! --Patrick
>


lgwalker_at_mts.net
bigwalk_ca_at_yahoo.com
Received on Thu Oct 24 2002 - 21:54:57 BST