Tek TDS420 help?
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From: DaveC on 31 Jan 2010 15:16 This scope has the famous "FAIL ++ Acq" error which points to the infamous failed (and leaking) SMD caps on the acquisition PCB. I'm moving on to troubleshoot another (unrelated, I think -- and hope) issue. During the 25 second "on" period, relays click on & off, the monitor goes through it's boot display (all bright, then dark, then the clock icon), then the graticule is drawn, which is quickly replaced with the "Tek Running Autoing" display listing the "FAIL ++ Acq" error. During the power-up period, the front panel LEDs all turn on for about 25 seconds, then off for 5 seconds, then only the CH 1 LED lights. The service manual says (in the Front Panel troubleshooting chart): Do all of the front panel LEDs turn on and then turn off a short time later? (Then:) Does one front panel LED turn on and then turn off, followed by the next LED until all LEDs have turned on and then turned off? The LEDs do not go through this one-at-a-time sequence. The manual's flow chart points to a failed CPU PCB if the LEDs don't blink this sequence. Can someone with a TDS4xx confirm power-on LED behavior? I'm trying to determine whether, because the LEDs aren't blinking "properly" and most of the front panel buttons are not working (the buttons bordering the monitor, plus all the CH input buttons), does this mean a replacement CPU PCB is in my future, or if it's possibly related to cap failure (ie, other cap failures beyond the acquisition PCB)? Has anyone else here have a similar problem (non-functional buttons) in the past? I'd appreciate hearing your experiences. Thanks, Dave
From: DaveC on 31 Jan 2010 15:49 > All my experience is with the 540, but I think you're wasting your time > trying to troubleshoot ANYTHING OK, I suspected that, but non-functional buttons seemed a symptom not related to caps issue. But I'll take your advice to heart and do *all* the caps. > until you replace ALL, AND I DO MEAN > EVERY SINGLE ONE on every board, the caps and CLEAN > CLEAN CLEAN and CLEAN again the circuit boards. Yeah, I plan to do that. Making a complete list right now. What techniques and chemicals did you use? Thanks for your reply. Dave
From: DaveC on 1 Feb 2010 04:03 A little more info on my non-functioning button problem: I disassembled the front of the scope -- bezel, buttons, front panel assembly. The elastomer button strip (the "rubber' buttons) have a conductive backing which presses down onto the menu flex circuit (flex pcb). The back of the button looks good (very light wear indications). The flex circuit traces are not metal, which surprises me. It's made from pretty fragile carbon-like traces. When I measure the continuity of the closed contacts of a button that works, I see approximately 200 ohms. Closed contacts of a button that doesn't work, I see 400 ohms (sometimes more). What resistance should I see at the contacts when the button is pressed? Can I clean these contacts with alcohol? Or...? Can the traces on the flex circuit be renewed (ie, silver-bearing paint)? Thanks.
From: Wild_Bill on 1 Feb 2010 05:01 The method I use for cleaning those conductive pads on button switches (keyboards, IR remote controls, etc) is very lightly scuffing them with a pen-type tool that has strands of glass fibers in it. It can be difficult to determine the "normal" resistance of these types of contacts, because typically, the resistance decreases as more pressure is applied to the button. The button pads that are shiney, somewhat glossy, are the ones that need scuffing, IME. I lightly scuff the conducive pads just enough to remove the shine, sometimes just a few passes across the pads. I can never be certain how long the scuffing treatment will last. Most times the problem is corrected for at least a couple of months to about a year, maybe longer. The tool I use was found in a camera department of a retail store years ago, as a battery contact cleaning tool. I've read numerous comments that the same type of tool is available at autobody shop supply places, as a scuffing tool for small chips in in painted surfaces on car bodies. I would also like to know if any conductive paint-type products work effectively, and are somewhat permanent. -- Cheers, WB .............. "DaveC" <invalid(a)invalid.net> wrote in message news:0001HW.C78BD8D601BE4002B08A39AF(a)news.eternal-september.org... >A little more info on my non-functioning button problem: > > I disassembled the front of the scope -- bezel, buttons, front panel > assembly. > > The elastomer button strip (the "rubber' buttons) have a conductive > backing > which presses down onto the menu flex circuit (flex pcb). > > The back of the button looks good (very light wear indications). The flex > circuit traces are not metal, which surprises me. It's made from pretty > fragile carbon-like traces. > > When I measure the continuity of the closed contacts of a button that > works, > I see approximately 200 ohms. Closed contacts of a button that doesn't > work, > I see 400 ohms (sometimes more). > > What resistance should I see at the contacts when the button is pressed? > > Can I clean these contacts with alcohol? Or...? > > Can the traces on the flex circuit be renewed (ie, silver-bearing paint)? > > Thanks. >
From: JW on 1 Feb 2010 05:12
On Sun, 31 Jan 2010 12:49:09 -0800 DaveC <invalid(a)invalid.net> wrote in Message id: <0001HW.C78B2CC50195EC48B0B2D9AF(a)news.eternal-september.org>: >> All my experience is with the 540, but I think you're wasting your time >> trying to troubleshoot ANYTHING > >OK, I suspected that, but non-functional buttons seemed a symptom not related >to caps issue. But I'll take your advice to heart and do *all* the caps. > >> until you replace ALL, AND I DO MEAN >> EVERY SINGLE ONE on every board, the caps and CLEAN >> CLEAN CLEAN and CLEAN again the circuit boards. > >Yeah, I plan to do that. Making a complete list right now. > >What techniques and chemicals did you use? I use Simple Green with a good non-metallic brush, then follow up with 90% isopropyl alcohol. For the rubber membrane contacts VERY gently clean with alcohol and pat dry. On scope ACQ boards that have been badly contaminated I run 'em through the dishwasher rinse cycle first with no soap. I position them vertically which allows the sprayer to gut under the chips themselves, as well as allowing the contaminant to run off. Then I put it in front of a fan for an hour or so, after which I do the cleaning mentioned above. |