from Bob Feretich - Mar 1, 2006
We made very good progress yesterday working toward a valid reset state for
- Fixed bugs in the reset logic tree.
- Fixed bugs specifically effecting "WTM" and "WRITE mode" resets.
- Discovered a very convenient scope setup that is making troubleshooting
reset problems a snap.
- Place scope in storage mode
- Attach Channel A to the reset switch logic (before pulse generation)
- Set scope to trigger on Channel A
- Set sweep to 10 uSec/div. Some reset pulses are 1.5 uSec wide. The
scope will not store two channels below 10 uSec/div.
- Probe troubled logic using Channel B
- Use the TAU CE Panel "Reset" switch to stimulate the logic.
- Most common bug is a clipped (.3V instead of 6V) reset pulse caused
by a leaky transistor. I will send a separate e-mail discussing transistor
- We are seeing a very high density of failures (bugs per pound of cards
used in the logic function) in the TAU. If this continues it could become
a major problem. Some failures seem to be related to card handling and inspection.
The SMS logic cards used in the TAU seem different than the ones I have seen
used in the CPU logic We often have no spares of the TAU card types. That
means we need to troubleshoot each card if we suspect a problem and repair
bad ones before we can proceed. This has slowed the TAU debug process.
Tape Channel Analyzer Status:
- The "Go" latch is not being reset.
- I think that the RDD counter logic is not being reset, but I don't
know how much of it is supposed to be reset.
- Then we can start debugging manual initiation of simple (non-data moving)
TAU operations. I suspect that we will see similar failure modes on these
operations and that the above scope setup (but moving the Channel A probe
to the appropriate switch) will work well for debug.
- The Tape Channel Analyzer is working well in responding to simple selection
- We now think that we don't need to replace the 26LS32s that are sensing
response signals. Ron Crane has devised a way to compensate for their current
draw by adding one resistor to each signal. No unwrapping will be needed.
- Ron Crane believes that the -N response signals will not need 26LS32
- I would like one more debug session using the Analyzer before I make
the modifications to it. (I'm busy this weekend and can't work on it anyway.)
I will plan to add the threshold adjustment logic and compensation resistors
to the +P response line sense logic late next week. In the mean time, I am
learning PIC18 architecture and assembly language.
Can anyone come in on a day other than Wednesday next week? It seems that
there are too many cooks in the kitchen on Wednesday. I will be traveling
Friday (tomorrow) through Monday. I can come in on Thursday, Friday, or Tuesday
(in order preference). I will not have e-mail access during my travel so
potential coordination for Tuesday should use my cell phone ( 408-464-3286