29 Jul
2011
29 Jul
'11
4:51 a.m.
ard at p850ug1.demon.co.uk schrieb:
Err no. If you have an N930 terminator, a missing grant
won't cause a
bus error. The amchine should run properly with such a terminator
That's what I
expected, as the machine came with this terminator instaled in the tape controller. The
tape controller is in a separate box, so I moved the terminator into the CPU box, when I
pulled the UNIBUS cable from the CPU to the tape controller box.
(actuially, on a short Unibus, you can get away with no
terminator at
the
'far end' for testing. I don't recoemnd running a machine that way
though.
I suspected that I cold get away without terminator when the bus is limited
to the 9 slot CPU system unit. So I tried without terminator, but this made no
difference.
First quesiton. What is the ground lead of the
'scome conncted to ? Is
it
connected to the system 0V rail?
No, as I wrote. I'll recheck with the ground
clip connected.
These supplies do suffer from dried-up electrolytics.
Any electrolytic capacitor potentionally suffers from this problem, not only those
old ons. But sometimes even very old capacitors work well.
Mains-frequency
ripple is normally provblems with the capacitor at the
output of the
bridge rectifier (the very large one mounted horizontally on the PCB),
spikes at switching freqeuncy are often due to the capactiro at the
output of the 'brick'.
Thanks for the hints. I'll have a closer look
when I return to the machine.
If you have an ESR meter, it's worth checking
them.
I don't have an ESR meter. I'll try to find an other way of testing
the capacitors.