Witchy
Experienced Member
Hi folks,
I'm looking over an SWTPC S/09 6809 system for another museum, some of you may have seen me post about it on Twitter.
It was working up until around a year ago then something went bang, we don't know what. Since then the PSU caps have also given up - both 8V and 16V rails collapse at powerup. I don't think the two events are related. Currently I'm getting all 3 rails from bench PSUs and voltages are stable. There was a fault with the MC1488 transmitter on the MPS2 serial board which had taken out the +12/-12 regulators, this may have been the source of the bang. I haven't checked to see if the 6850 UART for channel A looks active.
Thanks to Michael Holley's documentation at deramp.com I've been able to do a lot of fault finding (clocks, RESET etc), but I'm still getting no signs of life on the 2812 terminal (which there is zero docs online for apart from a couple of posts here). Terminal is fine otherwise, if I put it in half duplex mode I can type and everything's echoed as it should be. With my breakout box on the RS232 port I can see it trying to transmit when I hit keys.
I put the MP09 CPU board on the bench running from an 8V DC supply and my scope showed active and correct-looking traces on all the address/data lines. However, if I put my HP1660a analyser on the CPU the signals just disappear like I'm sucking the life from it. Remove test clip and the board comes back to life. I've not seen that behaviour before.
Anyone know why my analyser may do this?
Cheers!
I'm looking over an SWTPC S/09 6809 system for another museum, some of you may have seen me post about it on Twitter.
It was working up until around a year ago then something went bang, we don't know what. Since then the PSU caps have also given up - both 8V and 16V rails collapse at powerup. I don't think the two events are related. Currently I'm getting all 3 rails from bench PSUs and voltages are stable. There was a fault with the MC1488 transmitter on the MPS2 serial board which had taken out the +12/-12 regulators, this may have been the source of the bang. I haven't checked to see if the 6850 UART for channel A looks active.
Thanks to Michael Holley's documentation at deramp.com I've been able to do a lot of fault finding (clocks, RESET etc), but I'm still getting no signs of life on the 2812 terminal (which there is zero docs online for apart from a couple of posts here). Terminal is fine otherwise, if I put it in half duplex mode I can type and everything's echoed as it should be. With my breakout box on the RS232 port I can see it trying to transmit when I hit keys.
I put the MP09 CPU board on the bench running from an 8V DC supply and my scope showed active and correct-looking traces on all the address/data lines. However, if I put my HP1660a analyser on the CPU the signals just disappear like I'm sucking the life from it. Remove test clip and the board comes back to life. I've not seen that behaviour before.
Anyone know why my analyser may do this?
Cheers!