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tezza
January 2nd, 2014, 06:30 PM
I've started to diagnosis a Challenger 4P cassette-based machine which was donated to me about 6 months ago.

The symptom is the classic garbage screen on boot up. This is actually normal for a Challenger, but pressing Break (with the shift lock) down is suppose to clear this to the C/W/M prompt (or similar...I can't remember exactly what you should see).

Anyway, Break does not do anything.

I've done some preliminary checks and the CPU is working...there is a clock signal and noise on the address lines. I've followed Mark Csele's "Debugging a 500-series system..." found here
http://192.197.62.35/staff/mcsele/OhioScientific.html#500Series

RESET by pressing BREAK does nothing. There is no sign of activity or change in the waveforms with a scope on /WE or /CS on the 2114 video chip lines, like there should be.

I'm now wondering if the keyboard is working?

The question is does anyone know how you can reset the machine (essentially the equivalent of pressing the BREAK key), from the board itself, perhaps by shorting a couple of pins?


Tez

falter
January 2nd, 2014, 07:41 PM
I've started to diagnosis a Challenger 4P cassette-based machine which was donated to me about 6 months ago.

The symptom is the classic garbage screen on boot up. This is actually normal for a Challenger, but pressing Break (with the shift lock) down is suppose to clear this to the C/W/M prompt (or similar...I can't remember exactly what you should see).

Anyway, Break does not do anything.

I've done some preliminary checks and the CPU is working...there is a clock signal and noise on the address lines. I've followed Mark Csele's "Debugging a 500-series system..." found here
http://192.197.62.35/staff/mcsele/OhioScientific.html#500Series

RESET by pressing BREAK does nothing. There is no sign of activity or change in the waveforms with a scope on /WE or /CS on the 2114 video chip lines, like there should be.

I'm now wondering if the keyboard is working?

The question is does anyone know how you can reset the machine (essentially the equivalent of pressing the BREAK key), from the board itself, perhaps by shorting a couple of pins?


Tez

Sure sounds like keyboard.. although I wonder if it's possibly bad RAM -- on a number of machines I have here, I could get them to the point where they'd init their BASIC ROMs and then freeze there because the RAM was bad.

I just got my 1P today -- and it doesn't do that screen garbage thing either of your Challengers do. When I turn it on, it is *instantly* at the prompt.. with an extra letter D there (I assume for the disk drive/controller that it came with). Lightning quick compared even to my Commodores.

tezza
January 3rd, 2014, 01:19 PM
Right. Progress.

My Challenger 4P does have a big red button by the BREAK key. I don't think this is a standard fitting. I suspect it's something a hobbyist has put in.

Anyway, if you press the BREAK key AND this red button it boots!! Yay!!

I've tried some BASIC code and it seems just fine. Nice to see that text in 64 columns as opposed to the 22 columns of my 1P.

Things are not totally fine yet though. I only get the standard 8k RAM on the CPU board (board 502) rather than the other 32k RAM. The 24k RAM expansion board (board 527) is not working. Possibly a faulty RAM chip. There are 48 of them! Something to diagnose.

Tez

tezza
January 4th, 2014, 01:32 AM
Would anyone have a scanned manual for the Challenger 527 24k RAM expansion board? There seems to be a series of dip switches missing (just the socket is present) and some weird home soldered jumpers (including one that is not connected to anything). I think I really need to know what these do.

http://www.classic-computers.org.nz/blog/images/2014-01-04-OSI-challenger-527-ram-expansion-800-600.jpg

I've verified the RAM chips are getting 5V anyway. The board simply doesn't add anything to memory.

Perhaps all switches are open if a full RAM set is present so no dip switches are needed?

Could be just a faulty chip at the start of the expanded RAM but what pair of RAM chips are at the start?

Tez

tezza
January 4th, 2014, 01:45 AM
BTW I've just found the schematic at
http://osiweb.org/osiweb/manuals/527_2.pdf

At least this shows me the start of the RAM on the board. I'll need to study it more to figure out what the dip switch and jumpers do though.

Frank S
January 4th, 2014, 01:55 AM
Hello Tez,
these switches selects the address (A16-A19) of the board.
If you have a plenty amount of this boards, the need for the switches came up.
The picture shows the kind of switch.
Frank
16684

tezza
January 4th, 2014, 02:19 AM
Thanks Frank. One question.

If I have a fully populated board with 24k, do I need these switches or can all switch connections be open (like they are now ....because there is no switch)?

Tez

Frank S
January 4th, 2014, 02:30 AM
Hello Tez,
if the jumper W4 is in the factory default position (Pin 4 and 5 from LS138 to ground), then there is no need to populate the position of the switch SW1.
You than have access to the board only in the first 64K boundary.
Frank
16685

tezza
January 4th, 2014, 02:46 AM
Ok, I'll check on that. Thanks.

I've noticed that the SAMS service manual for the 4P has a section on checking if memory chips on the 527 board are being selected, so I'll work through that.

Tez

tezza
January 9th, 2014, 11:46 AM
Right, I'm back on this project again, trying to get my Challenger 4P 527 memory board working. The C4P itself now seems to be working just fine.

Still the C4P fails to recognise the board when it's fitted. I've checked voltages and they seem fine. The board is certainly getting juice.

My hunch it, it's due to the jumpers (the mass of home-soldered red wires on the board in the previous photo). A couple of the wires are floating free...presumably these have been knocked off the point to which they were soldered.

I don't really understand where these jumpers are suppose to go though, as I've got no instruction manual on the board. The appropriate part of the circuit diagram from the SAMs book is here, where the jumpers are labelled W1, W2...etc.

http://www.classic-computers.org.nz/blog/images/2014-01-09-CP4-527-memory-board-jumpers.JPG

How do these work and what are they for? Are the connections suppose to follow the dotted lines, or the straight lines with the "X" in them? Does anyone know, or can guess just looking at this diagram? Frank has already mentioned W4, which is the default setting for this board, when jumpered across the "X".

Any thoughts welcome.

Tez

Frank S
January 9th, 2014, 12:16 PM
Hello Tez,
with W4 closed at factory default, you are in the first 64K segment.
You have with the 527 board 24K of memory.
W1, W2 and W3 decide, where to put the 24k block of memory in the 64K range.
In detail you have three 8k blocks, you can put elsewhere, depending on the jumpers W1-W3
Frank

tezza
January 9th, 2014, 12:38 PM
I see. Thanks. That explains it.

Hmm...I'll have to dig out the memory map for this 502 board. I think it's different from the 505 board (with the disk controller) which would explain why jumpers are needed. But if I just connect them up via the lines where the "X" crosses, will this give me 3x8k continuous blocks from where ever the RAM stops on board 502?

Tez

tezza
January 9th, 2014, 01:05 PM
From what I've read it seems that the 502 board's onboard RAM stops at 1FFF. BASIC in ROM starts at A000, so the space in between can be used for more RAM.

Hopefully the memory checking routine on initialization on the 502 does go beyond the 8k on the board? Mostly these 527 boards were used with the 505s. Maybe the 502 doesn't check for expanded memory anyway, in which case it might exist and be usable, but there would be no indication of it on boot up!

These Challengers are definitely machines that are close to the metal, if you known what I mean!

Tez