| Electronics > Repair |
| Keithley 2002 repair help |
| << < (5/43) > >> |
| Samogon:
You went too far with recaping :) |
| Smith:
The new units have the same cap, but manufactured by BC. I replaced the cap on mine after replacing the VFD. It went bad within 8 hours and overloaded the 60v of the VFD. I placed the old Philips cap of the old VFD on the new VFD, and it's still working fine. |
| nikonoid:
Smith, thanks for the photo. This is right on. And here is my display board: As soon as I opened it, I could see signs of extreme overheating. See by the contact switches. The board became more transparent and showed rainbow colored fringe, sort of like you get with a drop of gasoline in the water. The damage almost looked worse on the switch side than on component side. The heat pattern seemed to be centered at Q901 component. It is near capacitor, but not directly next to it. The transformer also looked burned. That said when I powered the meter up, the display worked without any problems. Please let me know what you think. Here is the rubber keyboard. I cleaned it and switch contacts with IPA. The discoloration on rubber looks strange: When I removed analog board and lower shield, I also discovered another spot that looked like overheating. It is right at the spot where lower shield has a heat transfer sponge. It is in the lower right corner of the photo below and also magnified in the photo after, where I was able to photograph rainbow discoloration on the board. What could it be? Should I be concerned? Here is a quick grab of the back of a digital board and also the ESD safe sponges I used with IPA for cleaning: And finally the badge of honor 8) Please let me know if you have any ideas about two overheated spots (display and analog boards). Thank you. |
| Le_Bassiste:
yes, these pesky VFD transformers are real cookers! don't know how to handle that, though. as for the discoloration of the area under the heat sponge, that is not caused by overheating. it is caused by the sponge itself, sweating out some of the silicone over the years. if you look closely, you will find traces of that on top of the pcb as well, where it crept through the vias. the extra conformal coating on the pcb in the area, where the sponge sits, was discussed before: https://www.eevblog.com/forum/repair/repair-94'-keithley-2002-8-5-digit-dmm-good-ol'-cap-leaks-destuction-derby/msg1016968/#msg1016968 i _assume_, that the seemingly useless and contradicting application of the coating over guard traces was intended to protect that area against moisture getting trapped underneath. so, i would go with TiN's notion here: leave as is. edit: see also: https://www.eevblog.com/forum/repair/repair-94'-keithley-2002-8-5-digit-dmm-good-ol'-cap-leaks-destuction-derby/msg1017683/#msg1017683 |
| Le_Bassiste:
hmm, after another look at your photos, i now see that it is not the transformer that caused the brown spot on the pcb, :palm: it's one of the two push-pull transistors on the primary side. given the age of the instrument and the fact that the supply of the display is still giving the right voltages for filament and anode, you probably shouldn't be too worried about it. the only thing that you could do is to exchange the transistors with some better ones. don't know from top of my head whether these are BJTs or MOSFETs, have a look at the KEI2001 schematics (VFD supply should be same as in KEI2002, but is located on digital board) on TiN's site to find out. |
| Navigation |
| Message Index |
| Next page |
| Previous page |