[Coladam] eBay auction

Geoff Oltmans oltmansg at bellsouth.net
Sun Jun 14 02:43:02 CEST 2009


I agree with your assessment. It is clearly as you say though, a  
68701, 1k sram, and an address latch and inverter. This appears  
numerous times in the ADAM design for ADAM Net. I agree, didn't see  
any evidence of the LM339 and associated circuitry (which would  
definitely involve some inductors as well).

I wonder if there's any of this circuitry underneath the ribbon cable.  
It is rather large.

The puzzling thing to me is that some of the chips appear to be some  
interface chips to/from the Z80 bus/expansion connector, which of  
course you wouldn't/couldn't need for a simple ADAM Net device. Near  
the expansion connector, I make out two 74LS138s (3-to-8 decoders), a  
74LS125 quad tri-state buffer, and a 74LS175 quad D flip flop.

I believe the small 8 pin chip is an LM347[?]N. Most likely an op-amp.

There's an RCA CD4057BN(?) which is described as a 4 channel analog  
mux/demux with logic level conversion. I can't make out the chip above  
that.

I'm tempted to ask the seller to identify each chip.

eBay is not difficult to use. You can set up an account easily and  
you're good to go. As Joe mentioned, the best strategy for winning an  
eBay auction is to wait 'til the last possible second and place the  
max bid you're willing to accept. There are a variety of reasons for  
this:

1. eBay uses a proxy bidding scheme. What this means is that if I want  
something, I can place a maximum bid and eBay's system will bid up to  
that amount on my behalf. So, for example if the current bid stands at  
$10, and the current high bidder enters a max bid of $15, you come in  
and say bid $14 max, the original high bidder will still be the high  
bidder at $15. I would have to bid up one step above the original high  
bidder's bid in order to have the high bid. Another example, if the  
current bid was $10 (with a max of $15) and I bid a max of $30, the  
high bid would go to me at $16.

2. Knowing 1, we can see that anybody can simply "bid up" an item by  
whittling away at your max bid by placing incremental smaller bids up  
to (and possibly) beyond your max. I bid $11, the original bidder goes  
up to $12. Then I bid $13, the original bidder bids $14, and so on.  
This can include sellers who either have a second account set up (or a  
buddy) to bid up items they feel aren't selling for what they should.

3. Knowing 2, there are "sniper" bidders and/or special software that  
will wait til the last 30 seconds or so of the auction to place either  
a max bid, or whittle away at your max until they just surpass it.  
This gives you little opportunity to counter bid and they win the  
auction.

Clearly the best bidding strategy for eBay is to wait til the last few  
seconds of the auction, and place the biggest bid you're willing to  
pay. This gives you the best chance of paying the lowest price and  
winning an item.

I would like to see the guts in person (or higher res pics), beyond  
that though I'm unwilling to pay what this would ultimately go for I'm  
sure. It would be a nice piece to have for a collection, but I'm  
unsure what additional information can be gleaned about the ADAM  
architecture by having it.


On Jun 13, 2009, at 3:34 PM, Rich Drushel wrote:

>
> On Fri, June 12, 2009 8:26 pm, Frances and/or Richard Clee wrote:
>
>> Meanwhile, the series of disassembled, closeup pictures is posted so
>> perhaps Rich or geoff or Dale or someone can figure out what the damn
>> things are, and if the better interests of the Adam community  
>> suggest we
>> pursue them.
>>
>> So will those who know please speak up?
>
>     Okay, now that my brain is clear (turns out I was in the onset
> stages of a migraine when I was writing last time, eventually my  
> vision
> almost went out and my head was exploding for a few hours, ask Rin how
> much sense I was making at the time), and I have had a chance to  
> examine
> the disassembly photos, here is what I think:
>
> (1)  The most informative photo is the one with the diagonal color  
> ribbon
> cable, since that exposes much more of the underlying circuit  
> board.  I
> will refer to this photo in subsequent points.
>
> (2)  The large 40-pin ceramic DIP marked "TAPE SIM", with its  
> associated
> chips (TTL logic 74LS273 and 74LS00, 2 static RAMs 2114) and metal  
> oscillator
> crystal, is clearly is 60701 microcontroller (EEPROM version of the  
> 6801),
> suggesting that the board is an ADAMnet device.  Somewhere around  
> should also
> be an LM339 quad comparator, a 14-pin DIP, which was always part of  
> the ADAMnet
> interface.  Possibly it is under the multicolor ribbon cables.  If  
> it is absent,
> then whatever the board originally did, it cannot in its present  
> state be a
> functional ADAMnet device, because the LM339 sits between the  
> ADAMnet bus and
> the 68701 -- it would never get any ADAMnet inputs.
>
> (3)  The circuitry in the vicinity of the added DB-37 connector,  
> especially
> the blue rectangular trimpot (i.e., high-precision variable resistor  
> with
> a tiny adjustment screw sticking out horizontally), suggests to me  
> that
> maybe the original board was a prototype for a disk or tape drive.   
> I have
> looked at the extant schematics
>
>     http://drushel.cwru.edu/schematics/
>
> but don't see any immediate matches to the chips whose names I can
> read in the disassembly photos.
>
> (4)  I count 19 wires in the top ribbon cable and 15 in the bottom  
> cable
> (composite of both disassembly photos).  That would leave 3 unused  
> pins
> on the DB-37 connector.  Very likely the signals are 16 address lines,
> 8 data lines, 2 ADAMnet lines (data and reset), and presumably other  
> Z80
> control signals of interest that get run out the sideport connector.
>
> (5)  The circuit board appears to have been designed to fit into the
> Expansion Module #1 case, even though the board is clearly *NOT* a
> reworked Expansion Module #1 board.
>
> **** WILD GUESS ****
>
>     The circuit board was originally for prototype tape drives,
> either as a prototype of the (apparently planned, since there are
> ADAMnet device numbers reserved for them) tape 3/4 expansion unit,
> or else for original development of tape drives in general.  Given
> how fragile the existing connectors are for the tape drives (plus
> the pain of installing them in the first place), I can imagine a
> sideport-based unit being easier to plug/unplug during development
> cycles.  The "TAPE SIM" 68701 just runs a dummy tape drive device
> (or devices).  At the ADAMnet level, all the user cares about is
> reading and writing data, and if the 68701 does what is expected,
> then it doesn't matter that there is no real tape drive attached.
>
> ***** END WILD GUESS *****
>
>     I personally would like to have one of these devices.  But
> as stated before, I have never used eBay, so I am the wrong person
> to ask about bidding.  But I am willing to contribute $$$ to someone
> who knows how to win eBay auctions :-S
>
>     *Rich*
>
> -- 
> Richard F. Drushel, Ph.D.            | "They fell:  for Heaven to  
> them no hope
> Department of Biology                |  imparts / Who hear not for  
> the beating
> Case Western Reserve University      |  of their hearts."
> Cleveland, Ohio  44106-7080  U.S.A.  |         -- Edgar Allan Poe,  
> "Al-Aaraaf"
>
>
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