RE : SLC-5/04 no power supply to processor

Facing the following problem with a SLC-5/04 set-up:
The main source is taken from a UPS power supply!
What happens is that for an unexplainable reason the power supply to the CPU is lost (24Vdc) when measuring the voltage on the SLC power supply, removing the power card and the CPU brings back the 24Vdc! however the program is lost and needs to be uploaded again and again!
Any logical explanation of what might go on?
Thanks

1. How often does this occur?
2. Is there a common event that preceeds the failure?
3. If either the power supply or cpu are pulled individually, will it reset?
4. Have you tried replacing either one?
5. Do you have the means to monitor/record the UPS output to the SLC?


Most UPS's will trip if thier capacity is exceeded for a period of time. 110% for 10 minutes, 150% for 1 minute or some such. Sounds like you may have a bad power supply, CPU or chassis. It could be heat realated, it could be a piece of debri, it could be a lot of things.

Until you solve the riddle, you could install a EEPROM memory module,
set the cpu to read it every time and go to run. The downside is you will lose any on line edits next time the cpu is powered up.

Thanks Ken for your reply.
It did happen a couple of times on two different systems but with same hardware configuration.
The UPS is confirmed stable and no alarms occured at the time of the incidents (incident is at a Wafer fab).
We can almost certainly exclude a power glitch as no other equipment was effected.
The wierd thing is that the DC supposed to come from the 1747-P2 is not present resulting backplane and I/O cards without power.
To have the DC recovered we need to remove the CPU, (is there some logic from CPU that prevents the power to come on?
Also after installing the CPU back into the rack the program is lost eventhough a new bat is installed and no fault indication on the CPU?
As for the heat dissipation, equipment is installed in a aircon controlled environment!
It would be difficult to convince customer to have all 300 similar products have an EEPROM installed!
Thanks.

Power Lose

I am not sure what is going on. I think I would start switching things out. Have you tried a different P2 power supply? It also could be a problem in the backplane of the rack. Less likely would be a faulty processor or a bad battery connection.

I had a problem once with a bad surge strip causing power problems. Have you tried a different UPS?

are you using the 24v from the rack power supply for anything? ( are wires connected to the 24v terms of the rack supply)
I have seen with certain power supplies that when that 24v gets shorted you have to power down long enough to let the supply caps drain down then with no removals or changes as long as the short no longer exists it powers up fine. It does take a while for the caps to drain as there must be some protection that disconnects all loads.

Drewcrew6

You probably have a short circuit occurring in the wiring that is attached to the 24 VDC auxilary terminals from the 1747-P2. Such a short circuit will cause a "crowbar" protection circuit to engage and will put the 1747-P2 in shutdown mode until power is totally removed. It may also result in the CPU program clearing.

To have the DC recovered we need to remove the CPU, (is there some logic from CPU that prevents the power to come on?

Click to expand...

Remember: you should NEVER remove an SLC controller from the rack unless power has been removed from the 1747-P2. It doesn't matter if you don't measure 24 VDC on the external terminals of the -P2; the 5VDC part of the supply may still be active and you can damage your CPU.