TS1000 white screen but no K

[Paul]

I found an AT28c256 chip and tried wireing it up

Once you are leaving the 8K Size ROMs I can recommend the Winbond W27C512 chips. They are 100% pin compatible to 27C512 (and smaller) and are EEPROMs which can be erased and programmed easily with any recent eprom programmer.
Price is low and they work very reliable.
Kind regards
Paul

[mrtinb]

I have used this Arduino shied to “burn” my EEPROMS. http://web.archive.org/web/201711091044 ... prommer-en

[junkman]

Well I wired in my 27c64 after burning it....

At least I got something more then a grey screen

If I reset the CPU it seems to reset for a second and I get different patterns.

[1024MAK]

You may have already done this, but double check all connections using a multimeter on a resistance range between the EPROM pins and the relevant Z80 CPU / ULA pins (keeping in mind the series resistors).

Mark

[junkman]

Thanks. Yes checked the A and D busses between the chips. I can't find a fault. My last hope is the RAM is bad somehow. I have a 6116 chip on order.
The only other thing I can think of is I am somehow burning the EPROM's wrong.

[1024MAK]

You should be able to read back the EPROM in you programmer, then compare the read back file and the original on your PC using a suitable application (I use a Hex editor so I can see which bytes are different).

I presume you either used an adapter board / socket, or bent the pins out and hardwired the amended wiring or cut tracks and hardwired the PCB, as a 27C64 is not fully compatible with the ROM pin-out.

A RAM fault in most cases results in a completely blank screen.

Mark

[Moggy]

A point to note is that pins 1 , 27 , 28 have to be held at 5v.
When hard wiring the chip the method I use is to bend out these three pins so they are not socketed then solder a short wire from pin 1 to 28-27 and also 26.
Pin 26 is not connected internally but the socket hole on the board it fits into, conveniently is at 5v so leave pin 26 socketed and this will provide the needed 5v for the three other pins. a few more pins also have to be swapped.
Pins 2, 20 and 23 are raised then pin 2 links to socket hole 23, pin 14 links to raised pin 20 then a link from raised pin 23 to socket hole pin 20

Hope this makes sense as I'm not the most technically minded.

[junkman]

Thanks for the reply.
I have 1, 27,28 to 5volts.
26 NC
And 20 to GND 14.
I bent the address pins out that need changing and am using an edge connector to temporally rewire the ROM chip rather then modifying the board. I am still waiting for the 2363/2764 adaptor board.
I am then checking my work by ohming between the rom chip and the CPU lines.

Mark,
I am importing the rom file with these default settings. The software has a verify option that reads it back and it passes. This software is what I am unsure of. I may trying making a rom for a different machine just to see if what I am doing is working. My tandy color computer has socketed roms iirc.

[Moggy]

Have redited above post to show all links and pin changes.

[Moggy]

Just a thought.

It's not a PAL v NTSC thing is it?
I know there is a forth ROM for both standards so does the US model require an NTSC ROM image for different display timings etc?

I ask in all ignorance.