Troubleshooting

So your good old TI does not feel good recently? Or you have bought a console or expansion on the Internet and wonder whether something is wrong, or whether you just don't use it correctly?

We will discuss some trobleshooting strategies on these pages.

Video issues

Sometimes you can find weird screen outputs on real TI consoles, some of them shown on Ebay. In most cases the problem is a defect RAM circuit. The video memory is implemented by 8 circuits of TMS4116 (16K x 1); that is, each circuit hold exactly one bit of each byte.

Thanks to MESS, we can simulate various failure symptoms. For instance, when we apply an AND operation with byte 0x7F to every byte written to VDP RAM, the effect is the same as if the memory circuit for the leftmost bit has died - because the binary representation of 0x7F is 01111111. Likewise, if we AND the value 0xBF on each byte (0xBF = 10111111), the result should look as if the second RAM circuit is defect.

From experience we can say that dead circuits should cause these stuck-at-0 symptoms; we never saw a stuck-at-1 or other cross-dependencies.

• Video RAM failures
• 

  Mask 01111111

• 

  Mask 10111111

• 

  Mask 11011111

• 

  Mask 11101111

• 

  Mask 11110111

• 

  Mask 11111011

• 

  Mask 11111101

• 

  Mask 11111110

If you found your screen output in this gallery, you will have to replace the failing video RAM circuit on the board. The video RAM is on the left side:

The image shows the bit numbers on the circuits. Note that Texas Instruments uses a big-endian bit order, i.e. bit 0 is the most significant bit (2⁷), and bit 7 is the least significant bit (2⁰). Accordingly, if your failure symptom is Mask 11011111, this means bit 2 is stuck at 0.

Disk-related issues

TI BASIC error codes

Error codes are two-digit codes like

I/O ERROR 56

First digit: Command which failed

0	1	2	3	4	5	6	7	8	9
OPEN	CLOSE	INPUT	PRINT		OLD	SAVE

Second digit: Error type

Code	Meaning	Explanation
0	Device not found	The specified device could not be found in the system. This may happen when you spelled the device name wrong (like DKS1) or when you wrote it in lowercase.
1
2
3
4
5
6	Device or media error	The drive may be defect, the floppy disk scratched, the cables broken. Also, the floppy disk may require to be reformatted or replaced. This error is not caused by an improper use of the command but has physical origin.
7	File error	The specified device was found, but not the file. Maybe the file name was misspelled or written in the wrong case.

The lowercase issue is a particularly attractive trap for new users. The TI systems define everything in uppercase (with depressed Alpha Lock), the lowercase letters are mostly used for text display. Also, the lowercase letters are shown as small capitals. In doubt, write DSK1 with Shift held down.

Controller error codes

These are the error codes from the PHP1240 Disk Controller Card (the original TI disk controller). They are usually only seen during operations of the Disk Manager cartridge.

Operation	Code	Meaning
Various operations	06	Device error, like track 0 not reached, no READY signal
Read Sector	07	Invalid sector number
Seek	11	Wrong track ID in header
Read Address (also during Read Sector)	06	Wrong side in header
	21	Sector header not found
	22	CRC error in sector header
	23	Byte buffer overflow (failure to fetch byte on time)
Write Sector	28	Compare error (data)
	31	Sector header not found
	33	Byte buffer underflow (failure to deliver byte on time)
	34	Write protection