computer controlled language laboratory help

[b]

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: http://www.fileden.com/files/2007/6/4/1143893/asc lab 1 new.jpg
part 2. http://www.fileden.com/files/2007/6/4/1143893/asc lab 2 new.jpg

print side of the pcb: http://www.fileden.com/files/2007/6/4/1143893/asc lab print side new.jpg

There are some pictures of the equipment here:
http://www.fileden.com/files/2007/6/4/1143893/console1.jpg
http://www.fileden.com/files/2007/6/4/1143893/console underside.jpg
http://www.fileden.com/files/2007/6/4/1143893/console elements.jpg

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

 

[Franc Zabkar]

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: http://www.fileden.com/files/2007/6/4/1143893/asc lab 1 new.jpg
part 2. http://www.fileden.com/files/2007/6/4/1143893/asc lab 2 new.jpg

print side of the pcb: http://www.fileden.com/files/2007/6/4/1143893/asc lab print side new.jpg

There are some pictures of the equipment here:
http://www.fileden.com/files/2007/6/4/1143893/console1.jpg
http://www.fileden.com/files/2007/6/4/1143893/console underside.jpg
http://www.fileden.com/files/2007/6/4/1143893/console elements.jpg

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

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

 

[Franc Zabkar]

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 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.

http://ourworld.compuserve.com/homepages/pvanleeuwen/ufhome.htm

- Franc Zabkar

 

[b]

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.

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€ 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

 

[Clint Sharp]

In message

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€ handling charge to deal with the problem, plus minimum a few
hundred for replacement parts (estimated).

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)