![Confused :?](./images/smilies/icon_e_confused.gif)
Oh! I just noticed 380nS is listed and I didn't have to work it out.
![Rolling Eyes :roll:](./images/smilies/icon_rolleyes.gif)
I went through your list and have done the tests but in hind site some of the scope tests might not have been valid given they were done with other faults on the board like the dodgy 15 MHz clock and EPROM connection. The problem I have with looking at the EPROM side of IC21 is that it is under the veroboard.martyn_hill wrote:a) a faulty DB Transceiver (LS245 - IC21) - pin 9 (more likely) or pin 11
If these look OK, I'd next replace the DB transceiver - taking the opportunity to insert a DIL socket in the process. Only then replacing the DRAM ICs...
I said pin 9 was more likely just because this is the 'private-bus' side of the LS245 DB transceiver - i.e. the one connected to the DRAM/8301, rather than the CPU & ROM - and from what has been described so far, seems to be the side of the bus most likely to have the fault.Ruptor wrote:Why do you say "pin 9 (more likely)" is this a common problem?
Pin 9 is DB0 (bit-0) on the private-bus, which connects to only DRAM ICs 1 and 9 plus the 8301 itself - as well as the DB Transceiver.Ruptor wrote:The strange thing is when the screen is updated with a new memory value pin 9 goes with logic signals so does that tell us which chip is faulty?
Um, what do you mean with "the OE input is not used"?Ruptor wrote:Then it hit me I can plug the home made EPROM in to the right hand ROM socket because the OE input is not used.
When Minerva updates the values on the screen every 10 seconds the line goes from about 1V to switching with data just like any other data line. I take this to mean that whatever writes to the display memory works but whatever reads doesn't see data and just gets zeros most of the time but because the level is around 1V a bit of noise particularly if the last data was a one causes the occasional 1 to come back. I guess that means it has to be the transceiver buffer driving pin 9 that is dead so nothing on pin 11 gets through.martyn_hill wrote:Pin 9 is DB0 (bit-0) on the private-bus, which connects to only DRAM ICs 1 and 9 plus the 8301 itself - as well as the DB Transceiver.
I'm not quite sure what you mean by "pin 9 goes with logic signals" - can you expand?
Yes CE not OE the one that has different polarity for enabling the different ROM chips. I was just thinking enable when I typed it not really chip or output I mean nothing would work if it was OE.mk79 wrote:Um, what do you mean with "the OE input is not used"?