sci.electronics.repair@googlegroups.com

Google Groups

vjp2.at@at.BioStrategist.dot.dot.com: Dec 05 10:11AM My 2007 AOpen PC would not turn on for months. I got a small flash when I pushed on and then nothing. Today I was surprised with a miracle, it turned on.   THe computer I am using right now (1995 GW2K) behaved similarly a few years ago and now works fine. (But it recovered more promptly).   WHich begs the question: do I need to replace both power supplies (one ATX, the other microATX)? If I turn the 2007 off in a few hours, will it turn on again when I return?   In both cases the culprit seems to have been prolonged non-use.   My uncle, a frail 86yo EE, insisted he could fix it by just finding the bad twenty five cent capacitor. And I've seen him fix bad capacitors by just tapping them. (He sepnt the 1950s on WW2 submarines the USA give Greece.)     - = - Vasos Panagiotopoulos, Columbia'81+, Reagan, Mozart, Pindus blog: panix.com/~vjp2/ruminatn.htm - = - web: panix.com/~vjp2/vasos.htm facebook.com/vasjpan2 - linkedin.com/in/vasjpan02 - biostrategist.com ---{Nothing herein constitutes advice. Everything fully disclaimed.}---

John-Del <ohger1s@gmail.com>: Dec 05 04:16AM -0800 On Thursday, December 5, 2019 at 5:11:08 AM UTC-5,   > My uncle, a frail 86yo EE, insisted he could fix it by just finding the bad > twenty five cent capacitor. And I've seen him fix bad capacitors by just > tapping them. (He sepnt the 1950s on WW2 submarines the USA give Greece.)   Old timers used to (allegedly) *fix* bad electrolytics by tapping them with the back end of a wrench. These were the metal chassis mount varieties, and banging them would compress what was left of the electrolyte inside. Squeezing with pliers was another option. Be aware that I heard of this as a lad back in the 1960s, so this would have been on older types caps, not what we see today.   Compressing those old style metal can caps might have bought some time but I think squeezing modern paper electros would do no good at all. When I get to work, I'm going to try that on some bad caps and see if there's any improvement in value and ESR.   Getting back to your problem, I think gramps is right; it's probably a tired electro (that would be "swell"). These almost invariably work far better when heated, so if the brick was sitting in a warm area, it might spring to life. Alternatively, you can heat the brick with a hair dryer or heat gun to get it to work, but these are only temporary solutions. Crack the bricks open and change the electros with the bulged tops. That will get most running. If not, you'll have to either ESR or replace the rest of the caps. Lower value caps on the primary side of the SMPS bricks generally go weak but don't swell or bulge.

Ralph Mowery <rmowery28146@earthlink.net>: Dec 05 10:33AM -0500 In article <43ebb9f6-6c65-4e89-b64b-01e38ba0fdbe@googlegroups.com>, ohger1s@gmail.com says...   > Getting back to your problem, I think gramps is right; it's probably a tired electro (that would be "swell"). These almost invariably work far better when heated, so if the brick was sitting in a warm area, it might spring to life. Alternatively, you can heat the brick with a hair dryer or heat gun to get it to work, but these are only temporary solutions. Crack the bricks open and change the electros with the bulged tops. That will get most running. If not, you'll have to either ESR or replace the rest of the caps. Lower value caps on the primary side of the SMPS bricks generally go weak but don't swell or bulge.   I agree, many of the capacitors made for switching supplies seem to go bad. Often the tops will bulge out. Sometimes heating them will make the supply work but if you turn it off you have to heat them again.   I have replaced capacitors in several pieces of gear and that seemed to be all that was wrong with them. I had one piece of test equimpment I bought surplus. It was made around 1995 and cost about $ 50,000 back then . It was to test the older cell phones. Bought it a few years ago and sometimes it would take about 2 to 5 minuits to come on. It should start within a few seconds. Replaced about 5 capacitors in the power supply and now it starts up in a few seconds like it is suppose to.

Brian Gregory <void-invalid-dead-dontuse@gmail.com>: Dec 05 01:39AM On 03/12/2019 22:36, John-Del wrote:   > If it's old, it could use CCFL back lighting which has a small amount of mercury. I don't believe there's any in an LED based display.   > You may have cracked it if you closed the top and there was something inside just a wee bit bigger than the gap between the screen and keyboard/mousepad.   > If you can see the defect with the laptop turned off in a bright light on an angle, then the inside glass layer is cracked. These cracks do generally get worse. If it's a newish laptop, you can change the screen.   It'd be unusual if glass that was part of the display itself was cracked and it didn't seriously mess up the display, like large areas near the cracked not working much if at all.   --   Brian Gregory (in England).

vjp2.at@at.BioStrategist.dot.dot.com: Dec 05 09:47AM In <b6ec1ca0-1454-4df2-be2e-9e9c5b7d5a5e@googlegroups.com> by John-Del <ohger1s@gmail.com> on Tue, 03 Dec 2019 17:36:18 we perused: *+-On Tuesday, December 3, 2019 at 12:23:54 PM UTC-5, vjp...@at.biostrategist.dot.dot.com wrote: *+-> My laptop screen looks like it has two curving crisscrossing wite threads on *+-> it. Turned off, it looks like they are cracks, but not to the feel. Else *+-> works fine. Is it hazardous (eg mercury)? If I do nothing, will it get *+-> worse. I may have leaned on it, but don't recall any accident. *+->   *+-If it's old, it could use CCFL back lighting which has a small amount of mercury. I don't believe there's any in an LED based display.   *+-You may have cracked it if you closed the top and there was something inside just a wee bit bigger than the gap between the screen and keyboard/mousepad.   *+-If you can see the defect with the laptop turned off in a bright light on an angle, then the inside glass layer is cracked. These cracks do generally get worse. If it's a newish laptop, you can change the screen.   Many thanks. It is a ten year old Acer Aspire ONE>   - = - Vasos Panagiotopoulos, Columbia'81+, Reagan, Mozart, Pindus blog: panix.com/~vjp2/ruminatn.htm - = - web: panix.com/~vjp2/vasos.htm facebook.com/vasjpan2 - linkedin.com/in/vasjpan02 - biostrategist.com ---{Nothing herein constitutes advice. Everything fully disclaimed.}---

Rob <nomail@example.com>: Nov 29 02:33PM > supposed to get though a 100K resistor and be able to do > anything?   > Replace the 220 ohm resistor with another 220 ohm.   Better first find out why the other one blew. It is likely that a decoupling cap (tantalum?) downstream has failed.

tubeguy@myshop.com: Nov 29 06:13AM -0600 Its a Sansui 5050 receiver. The power amp works, the radio tuning meter moves, so it seems that works. But the preamp board is dead. Not a single transistor or any other component on that board has voltage. There is 44vdc on a wire from the power supply. It goes to a resistor. No voltage on other side of this resistor. Multimeter on ohm scale confirms resistor is open.   The problem is that resistor is red red brown @ 5% (gold). Thats 220 ohms. Yet an online schematic shows R601 as 100K.   OK, I know that resistor is dead, but how can the actual color code be so different from schematic? The resistor is not burnt, but may have gotten warm. Yet the color code is plain to see, except the gold band is kind of greenish.....   My plan is to clip in a resistor, but where do I start with such a conflict of values....   Yes, I triple checked this is R601. Unless the schematic is labeled wrong????   This appears to be the only voltage source to this board.....   Any ideas or suggestions?   Thanks

Trevor Wilson <trevor@rageaudio.com.au>: Nov 30 07:07AM +1100 > This appears to be the only voltage source to this board.....   > Any ideas or suggestions?   > Thanks   **R601 is a 220 Ohm 0.5 Watt resistor. That is what is indicated on the schematic from Hi Fi Engine.   As others have stated, you need to use your noggin when fault-finding. For a 100k, 0.5 Watt resistor to show signs of stress (not burning) it would need to dissipate at least 0.5 Watt. That would suggest a Voltage drop in the order of 250 VDC across the resistor. Do you see 250VDC anywhere in that amp?   -- Trevor Wilson www.rageaudio.com.au

Tim Schwartz <tim@bristolnj.com>: Nov 29 08:37AM -0500 Looking at a schematic, there is an R601 on the F2646 Tone board (The one with the tone control pots) shown as a 220 ohm, 1/4 watt fuse resistor. There is a 100K R601 shown on the F2648 board schematic, but not the parts list, that I could find.   So, have a look at the manual and make sure you are looking at the diagram for the correct board, as there are (at least) TWO R601's in this unit. Or to quote a Canadian friend: "Clear as Mud, Eh?"   Regards, Tim Schwartz Bristol Electronics

bje@ripco.com: Nov 28 11:19AM > If the side that was higher is now lower and vice versa, you have an open > lamp(s) in the display. You might be able to find CCFL tubes on line to > replace them.     Thanks for passing along the info and it makes sense to me.   I didn't know the bulbs could go bad like that (even though when the set is on, the picture looks quite good with brightness and color temp).   I really doubt I'll proceed any further, I tried that lamp replacement once with a laptop and it didn't go well. Having all the different video inputs is handy but that really is the only thing going for it.   But since vga and dvi connections are becoming rare what is the point.   thanks again,   -bruce bje@ripco.com

Cursitor Doom <curd@notformail.com>: Nov 28 08:55AM > the design, they are far less effective with outgoing surges. And, if > you have, in fact, a drop in voltage due to a hard-start, the will have > no effect at all.   It's more likely a spike from the motor current being suddenly shut-off. Remember motors are reactive components.       -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.

Cursitor Doom <curd@notformail.com>: Nov 28 08:53AM On Wed, 27 Nov 2019 06:43:28 -0800, bruce2bowser wrote:   > Hook the fridge up to a surge protector.   If it's the back EMF from the motor as I assume it will be, then it'll be a spike, not a surge, and that requires a different approach.           -- This message may be freely reproduced without limit or charge only via the Usenet protocol. Reproduction in whole or part through other protocols, whether for profit or not, is conditional upon a charge of GBP10.00 per reproduction. Publication in this manner via non-Usenet protocols constitutes acceptance of this condition.

three_jeeps <jjhudak@gmail.com>: Dec 04 10:13AM -0800 On Thursday, November 21, 2019 at 9:33:26 PM UTC-5, Fox's Mercantile wrote: > Jeff-1.0 > WA6FWi > http:foxsmercantile.com   In this case, the 'river to the ppl' took a wrong turn. with all due respect, FANUC 3T tells you almost nothing wrt what the OP is trying to do. One needs to open the box and find out what CPU is on the main board e.g. intel iX, ARM X, Atmel, etc. etc. Knowing the CPU defines the ISA of the machine, and one can begin to figure out how to set up a logic analyzer to look at the machine instructions and execution. Configuring a small, simple ladder logic example or 5 and observing the instruction and address trace will provide some insight into what is being R/W to memory, EPROMS, etc. which can then be used to identify and decode the ladder login mnemonics used by the mfg. From what I know, the approach taken to codify and execute ladder logic mnemonics is unique to the mfg. There are some general schemes/patterns used to execute the ladder program but again, every mfg has their own way of doing things. If you really need to do things at this level, it is a LOT of work and a fair amount of guessing. There have been a number of academic papers looking at various issues wrt Ladder Logic in general and in some cases, manufacturer specific details are sometimes contained in the paper. Perhaps googling may help you. A JTAG connection and associated diagnostic software may be helpful as well. Good luck J

three_jeeps <jjhudak@gmail.com>: Dec 04 10:19AM -0800 On Wednesday, December 4, 2019 at 1:13:59 PM UTC-5, three_jeeps wrote: > A JTAG connection and associated diagnostic software may be helpful as well. > Good luck > J   I just saw the reference to the 8086 processor. the good news is that there is lots of knowledge about this processor, including how to use a logic analyizer with it. I believe that looking at a static ROM dump of contents may not provide you with the insight for what you want to do. Looking at execution of the system would be more beneficial. But again, a LOT of work J

You received this digest because you're subscribed to updates for this group. You can change your settings on the group membership page. To unsubscribe from this group and stop receiving emails from it send an email to sci.electronics.repair+unsubscribe@googlegroups.com.