Unable to get the Disk Mon menu

[Geoff Healey]

Hi, I am hoping for some suggestions/help.

I have built the disk controller with the V1.1 board but after much checking I have no luck getting it to display the mon menu. I have included some pics of the link/switches and the status of the USB-UART and a screen capture of what I get occasionally on the PUTTY terminal but here is a summary of what I have experienced.

 If I connect the PC to the UART before turning on the ALTAIR both leds (I assume TXRX) are on. Turning on the ALTAIR will most likely cause the brighter led closest to the disk cable connector to go off but pressing a key on the PC will cause the dimmer one next that flash. On other occasions both leds on the UART go off when the ALTAIR is turned on. I hold the monitor, momentarily push the reset and continue to hold the monitor I never get the prompt or any other characters on the screen no matter how long I hold the monitor (minutes in some cases). I do sometimes get some output with the return key (no other keys output) and I have attached a screen capture of that. If when turning on the ALTAIR both leds on the UART extinguish I never get any output to the screen but the dimmer led still blinks with keystrokes.

I have checked the board visually and with a multimeter for shorts and to ensure all the IC pins are in their sockets and all the components are of the correct value. The baud rate is 115200 8 bits, Ive tried all the flow control options in PUTTY but no change.

I guess the only unknown is the ATMEGA and if it is correctly programmed. I have seen mention of the fuses but I am not sure if following David Hansels instruction for those without a micropro programmer does set the fuses. I have programmed it via a UNO and tried both the MITS and ICOM hex files. Any confirmation of this would be good. https://github.com/dhansel/Altair8800-IOBus/blob/main/04-disk-controller/README.md

If there are any suggestions on diagnosing this I would be very grateful. What I am also not clear on is there any particular mode the ALTAIR needs to be booted in (switches etc) for the mon to be accessible via the UART. 

[M M]

1st drawn to the circle, but then it look like that ground short isn't connected?

[Geoff Healey]

Hi, The pic isnt clear but there is definitely a link between GND on the UART and GND on the board. And yes that solder joint looks dodgy but after checking / resoldering just to be sure no change in the status. Than you for pointing these out.