Hi Peter, Please read below from my technician. He has provided some very helpful information. Patty Smith -----Original Message----- From: Brown, Darryl Sent: Friday, October 14, 2005 7:14 AM To: Smith, Patty Subject: RE: defective S24 VME 524-6000-F02-00/ S24 VME,6u,7-SL,250w Patty Based on the symptoms presented, it would appear to be a potential power supply ripple/noise problem on the +5V. They will want to proceed with scope measurements on the supply inputs to the backplane. I would recommend the following scope settings: Horizontal Sweep @ 2mS, Vertical @ 20mV, Bandwidth limit @ 20 MHz. The noise and ripple should be 50mV or less per the VME spec. Typically, bit errors start to occur when the noise gets above 90-100 mV unless the boards are particularly sensitive. When the measurement is made, it is very important that the probe ground lead be as short as possible as the ground lead will act as an antenna and pick up radiated noise in addition to the actual conducted noise/ripple component. See the attached photo for an example of a typical measurement technique at the backplane. If they do find excessive noise on the +5V and do not want to return right now. I would suggest that they try adding decoupling capacitors across the +5V and Return power bolts on the backplane. I would start with a .1uf and a 10-50uf(low ESR). -----Original Message----- From: Peter Kammel [mailto:kammel@npl.uiuc.edu] Sent: Thursday, October 13, 2005 4:18 PM To: Smith, Patty Subject: defective S24 VME Dear Patty, Thanks for your help. Peter ---------------------------------------------- Symptoms: During data tranfer, we are losing bits. When testing the same VME module in two different VMW crates, there were no problems. Another VME modul showed similar bit erros sitting in the tracewell crate. Tests thus far: We have checked the power supply dc voltage and all were ok. We have not looked by scope yet, to check for excessive AC noise. We would very much appreciate advice on other checks we could perform. The VME is located at an experiment in Switzerland, where there is a local electronics group which could perform checks. Alas they don't have VME modules and software to run backplane tests. Prof. Peter Kammel / pkammel@uiuc.edu Department of Physics, Loomis Laboratory University of Illinois at Urbana-Champaign 1110 West Green Street, Urbana, IL 61801 Tel (217) 333-5424 / Fax (217) 333-1215
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