Hello everyone,
I've seen other forum posts on here and other blogs about this. I've also written some posts about this on the HP/Agilent and R&S yahoo group but I would like to talk about it here too as a reminder. Its a about
RIFA capacitors.
Basically a warning to check for them in older equipment and to replace them on site. It'll be located on the "hot" or "live" side of a power supply board. This needs to be addressed given how everyone nowadays is on ebay buying "reliable test equipment".
The story goes that I was using a HP 8561B to see all the types of frequencies used for chatter during Harvey's epic flooding here in Houston. My area became its own island by Sunday morning. On Monday, we were looking for chatter since I had accidentally left my radio equipment at another location or rather I decided to come to a safer location that coincidentally was where we had stored various HP equipment since its higher off the ground and never floods. Prior to the flooding, this unit was kept in a garage that could have been exposed to both heat and humidity. Prior to storage I used the unit for 2 years with no problems. It never got wet and fortunately water did not get inside the house. I took the unit to a room on the second floor. Alot of things went on the 2nd floor like the outdoor grill to the balcony, food to the minibar fridge, important document, etc.
I started to test the unit in the computer room on a strong fold up table with fire extinguisher near by in the room. I turned it on for a good 15 minutes to make sure everything was working. Had to check if the crystal was on frequency and everything was good. I turned off the unit and left it plugged in. While texting on a message board to 2 people in the area, I heard a crackle and then a large pop. Confused for a second I thought I left the unit on but the CRT didn't display anything. I immediately raced to the floor to unplug the unit from the wall. When I realized that I never left it on I got a nice whiff of RIFA's magic smoke. I knew this unit was older and it clicked that it might have the same caps I had replaced from our Tek 2467B. Even though that happened I press on to using the "newer" 8563E. Later on confirmed that this unit had newer caps in it and if that failed I had a 8563EC I could part out (damaged RYTHM unit). A few days after when the waters receded and things were settling down I found the time to open the unit.
On the time that I needed to use this the most and least expected it this happened is what happened.
Bingo. Same caps from the Tek 2467B. Both units made around 87 or 88. Currently right now its just sitting in a corner as is till I had gotten my order and when I find time. A previous order placed on Aug 23rd on Mouser in Dallas could not come till 9/8 due to the damage Harvey had caused to travel. An airport's runaways (KHOU) were completely flooded out and the other airport (KIAH) was used as foward ops base for relief while its surrounding roads were flooded. All vital roads (like I-10) going into the city were blocked by water.
The takeaway message here is to, as mentioned above,
check and replace all RIFA capacitors. Especially found on units from the late 80s and early 90s. These things crack from thermal stress and aging. This can help the cap blow the magic smoke even while plugged in and the unit is turned off.
Questions I have are this:
Does humidity play a factor into this? I'm thinking water vapor seeps into the cracks and disturbs whats inside to create a short from live to neutral. I've seen other forums but its generally inconclusive so far.
What were the designers thinking? This is just pure evil. They do claim that the caps are self extinguishing and therefore fire proof but I'd rather not test that along with the other surrounding components on the board. All the goo from that sprayed all over the surrounding parts.
Anything better? Currently, in a rush, I ordered basically the same thing from Kemet but it seems they changed the encapsulation. It went from yellow to clear gray. The caps on the 8563E/EC are also this grayish color.
Any other equipment besides the HP 8561B and Tek 2467B? Feel free to make a list. It'll definitely help.
Discuss safety measures? Normally I use a surge protector with a switch or a wall outlet connected to a power switch, even though I instinctively dove down to rip the power cord from the wall socket.