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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Discharging Capacitors Prior to ESR Meter Probing
I got the Dick Smith device and am ready to tackle jobs. What
techniques/hardware are being used to make sure that capacitors are properly discharged? I will be working mostly on older stereo equipment. My understanding is that the non-power supply caps will discharge after the equipment is turned off. For a typical cap to be found in this application, what would be a good way to survey the board and discharge the caps? What size and type resistor? I have a bunch of audio grade sandcast types from partsexpress, would these be good enough? Should I even bother or are these caps inoffensive? The power supply caps, which I am guessing are identified by size and proximity to the power source are a different animal. What should be done about these? |
#2
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Discharging Capacitors Prior to ESR Meter Probing
I just use about a 20w 1K ceramic power resistor from a scrap unit with some
leads soldered to it. Probably a little higher value than needed for audio work and a little lower than optimal for TV HV, but it is a good compromise that works fine for everything so far. One thing that I like about the Atlas and Sencore meters over the DSE (I have them all) is that you don't have to worry about it. Actually, I use the Atlas more than anything in the field and for protable applications. I like the size and the fact that you can get cap value readings. I still like to discharge the large PS caps and CRTs just for safety, but for the lower capacity and lower voltages I just let the meters designed to do so discharge them. You can get a dischage update for the DSE, IIRC. Leonard wrote in message oups.com... I got the Dick Smith device and am ready to tackle jobs. What techniques/hardware are being used to make sure that capacitors are properly discharged? I will be working mostly on older stereo equipment. My understanding is that the non-power supply caps will discharge after the equipment is turned off. For a typical cap to be found in this application, what would be a good way to survey the board and discharge the caps? What size and type resistor? I have a bunch of audio grade sandcast types from partsexpress, would these be good enough? Should I even bother or are these caps inoffensive? The power supply caps, which I am guessing are identified by size and proximity to the power source are a different animal. What should be done about these? |
#3
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Discharging Capacitors Prior to ESR Meter Probing
I soldered in two 600 volt diodes back to back across the probes input connectors on my Dick Smith ESR meter. About 1 or 2 amps rating would be OK. Connect one diode with the anode toward one probe connector and the other diode with the anode toward the other probe connector. I haven't had any problems in the 3 years I have been using my meter. The diodes do not seem to affect the meter reading. Hope this helps. John |
#4
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Discharging Capacitors Prior to ESR Meter Probing
"I just use about a 20w 1K ceramic power resistor from a scrap unit
with some leads soldered to it. Probably a little higher value than needed for audio work and a little lower than optimal for TV HV, but it is a good compromise that works fine for everything so far. " Like one of these? http://www.mouser.com/index.cfm?hand..._pcodeid=58822 |
#5
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Discharging Capacitors Prior to ESR Meter Probing
"I soldered in two 600 volt diodes back to back across the probes
input connectors on my Dick Smith ESR meter. About 1 or 2 amps rating would be OK. Connect one diode with the anode toward one probe connector and the other diode with the anode toward the other probe connector. I haven't had any problems in the 3 years I have been using my meter. The diodes do not seem to affect the meter reading. Hope this helps. " I saw this modification in the documentation that came with the unit. Let's say I placed the meter with this mod across a filter cap on a 120W audio amplifer without prior discharging, what would happen? |
#6
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Discharging Capacitors Prior to ESR Meter Probing
wrote in message oups.com... I got the Dick Smith device and am ready to tackle jobs. What techniques/hardware are being used to make sure that capacitors are properly discharged? I will be working mostly on older stereo equipment. My understanding is that the non-power supply caps will discharge after the equipment is turned off. For a typical cap to be found in this application, what would be a good way to survey the board and discharge the caps? What size and type resistor? I have a bunch of audio grade sandcast types from partsexpress, would these be good enough? Should I even bother or are these caps inoffensive? The power supply caps, which I am guessing are identified by size and proximity to the power source are a different animal. What should be done about these? When I used to repair PC monitors it was often necessary to discharge the SMPSU primary side reservoir cap, which could be charged to as much as 320V! The device I found best to dump this charge was a NTC thermistor, most monitors and some TVs have these as inrush surge limiting devices in the mains input circuit, the ratings vary considerably depending what you salvage them from, the cold resistance can be anything from a few hundred Ohms to about 12K, as the discharge current heats the NTC thermistor it's resistance falls to typically less than 10 Ohms and discharges the cap in a controlled manner - rather than blowing chunks out of the PCB track like when shorting it out with a screwdriver. |
#7
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Discharging Capacitors Prior to ESR Meter Probing
wrote in message ups.com... "I soldered in two 600 volt diodes back to back across the probes input connectors on my Dick Smith ESR meter. About 1 or 2 amps rating would be OK. Connect one diode with the anode toward one probe connector and the other diode with the anode toward the other probe connector. I haven't had any problems in the 3 years I have been using my meter. The diodes do not seem to affect the meter reading. Hope this helps. " I saw this modification in the documentation that came with the unit. Let's say I placed the meter with this mod across a filter cap on a 120W audio amplifer without prior discharging, what would happen? There's a slight possibility one of the diodes might fail S/C - but it should protect the ESR meter. |
#8
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Discharging Capacitors Prior to ESR Meter Probing
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#9
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Discharging Capacitors Prior to ESR Meter Probing
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#11
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Discharging Capacitors Prior to ESR Meter Probing
"Just check any caps that might be charged with a volt meter. "
You can do this with any digital multi-meter on any sized cap? No danger of damaging it, even when reading a power supply cap? |
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