UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post

SiriusHardware · 22nd Jul 2021, 8:52 pm

Nice manual!

I think that in the parts list the description labels for the 1N5711 and 1N4148 are swapped (5711 is Schottky, 4148 is small signal silicon).

It may be worth stating that it is necessary to use a 'plain' 877 and not an 877A, otherwise you get the 'double image' issue in graphics mode only. The reason for this was never resolved so the present solution is - don't use the 877A.

On the prototypes (Mine, Tim's) the capacitors from A0-A7 to 0V were never fitted and fitting them could have unintended consequences. The ones from A8-A11 to 0V were necessary - 180pf-200pf in my case, to resolve the problem where software attempting to write to a location in any given memory page would sometimes write to the same location in a different memory page as well.

The hope is that the buffers will remove the need for any capacitor bodge on the address lines, so initially either the buffers should be fitted and no capacitors fitted, or capacitors, suggested value 180pF, should be fitted from A8-A11 to 0V only and the buffers should be linked across.

I'll start looking around for the ICs at work tomorrow. I think I might have the 365 buffers, the '02 and the RAM already. I'll also have a hunt around the shops for some suitable jiffy bags.

Once you've assembled your own board you should be able to get it to output a signal initially by setting it to display the contents of the onboard RAM at 0200-02FF and 0300-03FF and applying 5V power. It should render the random content of the RAM either as graphics or characters, according to the state of the graph / char input.

22nd Jul 2021, 8:52 pm	#64
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,585	Re: Ortonview PCB Nice manual! I think that in the parts list the description labels for the 1N5711 and 1N4148 are swapped (5711 is Schottky, 4148 is small signal silicon). It may be worth stating that it is necessary to use a 'plain' 877 and not an 877A, otherwise you get the 'double image' issue in graphics mode only. The reason for this was never resolved so the present solution is - don't use the 877A. On the prototypes (Mine, Tim's) the capacitors from A0-A7 to 0V were never fitted and fitting them could have unintended consequences. The ones from A8-A11 to 0V were necessary - 180pf-200pf in my case, to resolve the problem where software attempting to write to a location in any given memory page would sometimes write to the same location in a different memory page as well. The hope is that the buffers will remove the need for any capacitor bodge on the address lines, so initially either the buffers should be fitted and no capacitors fitted, or capacitors, suggested value 180pF, should be fitted from A8-A11 to 0V only and the buffers should be linked across. I'll start looking around for the ICs at work tomorrow. I think I might have the 365 buffers, the '02 and the RAM already. I'll also have a hunt around the shops for some suitable jiffy bags. Once you've assembled your own board you should be able to get it to output a signal initially by setting it to display the contents of the onboard RAM at 0200-02FF and 0300-03FF and applying 5V power. It should render the random content of the RAM either as graphics or characters, according to the state of the graph / char input.