computer controlled language laboratory help

I am trying to get this analogue tape langauge lab system ASC model 4M up and running. I believe it dates from the late 80s. It consists of a master control panel and several 2-track slave decks. These are interfaced using a bus and ASCII command strings (that's as far as my knowledge goes on the IT side of things!).

schematic part 1:

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part 2.
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print side of the pcb:

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There are some pictures of the equipment here:

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The problem was caused on assembling the master panel's processor board: I accidentally connected the cable 105 which was supposed to go into connector 105 (from student control unit which supplies the slave decks) into socket 103 (they are the only two in the whole system which are the same size!). You can see on the schematic that pin 25 of 105 carries a +7.5v supply and 13-14-26 appear to have +5v on them. So these voltages were fed into the corresponding pins of number 103, and ended up God-knows- where, the 7.5v went on the AO line.

On powerup, a few lights came on on the console, but it was several seconds before I realised something was wrong and yanked the plug. Since then, the main console appears dead, with a very faint display on the LCD and nothing else. the individual slaves work, but receive nothing from the master console. The 'good' news is that since 105, which supplies a 5v and 7.5v supply, was not in its place, there were no other voltages around on that panel whilst the misconnection happened.

Could this be some eeprom got scrambled or one of the IC's blew? What I need to know now is what components are likely to have been affected by this misconnection, and what to start replacing. I tried replacing IC115 (8155) by subsitution from a student machine, no change. removing the ICs one by one (except IC108 to IC111) usually made no difference, but IC107 74HC138 caused the LCD to come on with garbage on, and a few random lights to come on. However, exchanging it for one of the others made the unit dead again.

ICs include.

74HC138AP SS74HC241E PC74HC00P D8259AG2 TMP8251AP D8505AHC-2 M74HC623B1 74HC573AP ULN2803A RAM: 6116 2764 27128

I know this is a long shot, any ideas on what to start replacing? I've no idea how easy to come by most those chips are. Thanks for any ideas B

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b
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On Thu, 5 Mar 2009 05:02:37 -0800 (PST), b put finger to keyboard and composed:

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The first parts I would check would be the EPROMs (2764, 27128). I presume the contents would include recognisable text strings, so if some text is garbled, then you can be almost certain that the PROMs are bad. For example, I would expect that a fault in address bit A0 would cause a text string such as "COPYRIGHT" to appear as "CCPPRRGGT" or "OOYYIIHH".

If reading the EPROMs several times produces different results, then once again you can be sure that they are bad. OTOH, if they have a zero checksum, or some other pattern that looks like a checksum (eg

0x55AA), then you can be confident that the part is OK.

If any of the EPROMS are bad, then you will need to find a working device to make a copy. In any case it would be a good idea to backup the contents of good devices to a file.

If you have difficulty obtaining any parts, I believe I may have a few of the bigger ICs in storage ... somewhere. Otherwise you may find that many of these ICs were used in old arcade games, IBM XTs, PC/ATs, etc.

BTW, IMO any design that allows you to do what you did is inexcusable. I wonder how many boards were destroyed in the factory in this way.

- Franc Zabkar

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Reply to
Franc Zabkar

On Fri, 06 Mar 2009 06:43:56 +1100, Franc Zabkar put finger to keyboard and composed:

If you don't have an EPROM programmer to read the EPROMs, then you may be able to install them in an old network card, in the boot PROM socket, and use Uniflash to read them.

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- Franc Zabkar

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Reply to
Franc Zabkar

thanks Franc. Yes, that design is dire. Using identical connectors which can produce such disastrous results if misconnected is ridiculous. they were the only two same ones in the whole pcb! Why on earth do designers do these things? I had the pcb on its back at the time and just didn't notice the socket was mismatched. To make matters worse, none of the darn things are labelled on the pcb in any way.

Anyway, I don't have an eeprom reader so will check out the link you suggest. never attempted anything like this before, but as it stands I've little to lose. I contacted the manufacturers, but they wanted a

1000=80 handling charge to deal with the problem, plus minimum a few hundred for replacement parts (estimated). Much as I like the gear, to invest that amount in a twenty year old system seems like a ludicrous proposition to me.

-B

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b

In message , b writes

Wow, where are you? I bet you could ship the board and all bits required to test it, have it fixed and returned for less than a third of that (providing the EPROMs are undamaged or a copy of the EPROM data is available)

Absolutely.

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Clint Sharp
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Clint Sharp

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