12 Jan
2019
12 Jan
'19
9:44 a.m.
On 1/12/19 11:31 AM, Bill Gunshannon via cctalk wrote:
On 1/12/19 9:20 AM, Bill Gunshannon via cctalk wrote:
Congrats on getting this part of the problem resolved.
Well, the problem is definitely bus grant as with just two memory
cards in the machine I put the disk controller in and it does not
show up in the Map. The only problem with this is the question
Why? I have examined the memory cards. The C-D (actually, C)
does have the bus grant lines connected. I even looked under a
magnifier to be sure the trace hadn't been cut and it is intact.
So, what else cold cause this?
(Another question, however, some cards have the ability to open
this. Why would you ever do that as it would break pretty much
any card that followed?)
Problem fixed. Note, fixed, not solved.
I dug out another MicroPDP BA23 box. Stuck the CPU in slot 1.
Started adding the memory cards one at a time and turning the
machine on waiting for the self-test and then doing a MAP.
Worked perfectly. The self test got slower as each memory
card was added and the map showed the block of memory and the
assigned CSR. So, what could go bad on a backplane to cause this
problem?
Or, could it be a power supply that is no longer delivering
the rated power?
If you haven't already, check the backplane slots for debris or corrosion on the
contacts.
Next with a voltmeter check the +5V and +12V first to see if the actual voltages are
within spec. If you have an oscilloscope, checking for excess voltage ripple. If the
power supplies have are using the original capacitors they might not be providing clean
power under significant load.
? Jerry