Problem - Bridgeport Series I CNC

[Rick Lindquist]

My son purchased a Bridgeport Series I CNC last October. The RS-232 interface did not work when we purchased the machine. Troubleshooting revealed that the line driver and line receiver chips on the ERS CCA had been blown. After replacing these chips, we powered up the machine and the RUN, GOTO, HOLD, and WAIT indicators remained illuminated and the machine would not function. Additional troubleshooting revealed that the BHALTL signal on the ERS CCA was at a logic low level, thereby halting the processor. We determined that the K7 connector on the ERS CCA was intermittent, thereby causing the BHALTL function to be invoked. This problem was corrected by installing a jumper to ground on the ERS CCA to bypass this interlock. After these corrective actions, the machine worked well for 3 months.
Recently, we again lost RS-232 communications with the machine. Oscilloscope measurements revealed that the line driver and line receiver chips are functioning correctly, but we determined that the UART oscillator was not working. Changing the UART crystal restored normal RS-232 communications. However, after the first power on cycle, the machine again locked up with the RUN, GOTO, HOLD, and WAIT indicators being constantly illuminated. Resetting and clearing the machine does not help. We measured the BHALTL signal on the ERS CCA and it is at a logic high level. Therefore, there must be another problem halting the processor. The humidity level in the shop is extremely high currently, and this may be wreaking havoc with the machine. Does anyone have any ideas as to what may be causing this problem?
Thanks,
Rick Lindquist

[machintek]

Probably the LSI-11 is haulted.

George

[Rick Lindquist]

George,
Thank you for your reply. Is there a signal other than the BHALTL, or a condition, that can cause the processor to be halted? The BHALTL signal on the ERS CCA was measured to be at a logic high level, and I believe it has to go low to halt the processor. I plan to measure the BHALTL signal directly on the Processor CCA.
Thank you for your help,
Rick

[Rick Lindquist]

We finally resolved the problem with my son's Series I Bridgeport CNC being stuck in the "Halt" condition at Power Up (RUN, GOTO, HOLD, and WAIT indicators being constantly illuminated). While in the Halt condition, normal machine operation is inhibited and the Octal Debugging Technique (ODT) state is entered. The console/computer has control of the machine (CNC provides "@" prompt).
Troubleshooting and analysis revealed that the ERS CCA was failing to assert the "BRPLY L" signal in response to the "BDIN L" data input transfer signal. The Maintenance Manual states that if a device fails to assert the "BRPLY L" signal in response to "DBIN L" within10 uSec, the processor enters the Halt state.
This problem was isolated to an intermittent connection on pin 10 of IC77 on the ERS CCA. This IC, unfortunately, is mounted on a socket in our CNC. After thirty some years of use the IC pins were corroded. This resulted in an intermittent connection with the socket pins. Careful removal of the corrosion restored normal system operation.
Another helpful hint that I want to pass on has to do with removing and re-seating the 5 processor ICs on the Processor CCA. Be careful to ensure that the IC pins are removed intact. We found that 3 IC pins had broken off and remained in the socket. This is simple to correct with a solder bridge or buss wire between the broken IC pin and the socket. I suspect that many years of use in a severe corrosive/high vibration environment weakened these pins.
I hope these "lessons learned" will help someone else experiencing similar symptoms.
Rick

[BOSS5]

Rick:
I've read your posts with the greatest interest, as I appear to be facing a very similar, if not almost identical problem. I'm really glad you took the effort to relate your experiences. My Boss5 is also asserting the HALT. It consistantly shows 70005 on start-up. (Did yours do this?). Like you, after experimenting, I cannot seem to communicate with the ERS at all. I've tried this on the local port at 2400 BAUD, tape reader unplugged just in case there were issues at that end. Please tell me the parity, stop bits and flow control you are using just to be sure I did not miss anything. I used Pins 6,7,8 on the local port. From your posting, I'm not able to decipher which IC's are the actual line drivers that you changed out on the ERS. Part numbers? Also which pin did you initially jumper to ground to force BHALTL high? (Do I assume logic high is ~ zero volts?). Where did you measure the BHALTL signal directly on the LSI-11? Aditionally, what replacement part did you use for the crystal oscillator and what test-points were you using to check it?
My board appears to have less corrosion than yours.
Greg.
PS: Do you have the Boss 5 Maintainance manuals and/or test tapes?

Greg.