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Re: Favorite bad capacitor debugging techniques?
You are right.
I have seen caps that lost allmost all capacitance with perfect ESR, i have seen caps that leaked over 15 mA at 350V, blew out a lot of dielectrium but still perfect ESR. I have seen caps with good capacitance, no leakage but bad ESR. I have seen a cap with a internal ripped or broken conductor. That lookes like severe dielectric absorbsion. ( is that called soakage ?) capacitance not possible to measure because you could not unload the cap. It gave 100 V on the voltmeter and even if you short it, no effect. I use a ESR meter just for fun, i like to examine components. In switchers I use it to test caps, not to find a problem. I used to do that but not any more. I measure with scope and DMM and as a result of that I most times find the problem. After I find it, and it is a cap I use the ESR meter, C meter and test DC leakage to be sure and for fun. Fred PA4TIM Op 31 aug. 2011 om 19:58 heeft "J. Forster" <jfor@...> het volgende geschreven: If a capacitor is pulling a bus down, an ESR meter is really not the right [Non-text portions of this message have been removed] |
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Re: Favorite bad capacitor debugging techniques?
J. Forster
If a capacitor is pulling a bus down, an ESR meter is really not the right
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tool. A short and a good cap both have a low ESR! -John ===============
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Re: Favorite bad capacitor debugging techniques?
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----- Original Message -----
From: "Pa4tim" <fredschneider@...> To: <hp_agilent_equipment@...> Sent: Wednesday, August 31, 2011 10:26 AM Subject: Re: [hp_agilent_equipment] Favorite bad capacitor debugging techniques? What model ESR meter you use ? I guess a HP bridgde. With 6.5 digits this is not one of the ESR "indicator" kits. How low can you measure. I use an analog meter, it goes upto 40 ohm ( but I made it non lineair for better resolution under 1 ohm, and accurate down to 100nF. But I think I change this and make it switchable between 1 ohm full scale and 40 ohm. ( not that this is important because if the meter corners it is good, the last cm on the scale is 1 Ohm so about 50 mOhm resolution) Fred PA4TIM FWIW, I usually check caps on a GR-1650-A but often leakage is important and is not measured by the usual impedance bridge. My usual arrangement is to use a small, regulated DC power supply and a meter capable of indicating quite low values of current. My Tektronix DMM goes low enough. I've found paper caps that test good on the bridge but have excessive leakage and won't work in some circuits. Leakage is a primary test for electrolytics. There _are_ capacitance bridges like the GR 1617-A that will also measure leakage and supply a variable bias internally but I don't have one. A megohmeter will also do provided you have one which will run at voltages suitable for the caps. -- Richard Knoppow Los Angeles WB6KBL dickburk@... |
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Re: Favorite bad capacitor debugging techniques?
What model ESR meter you use ? I guess a HP bridgde. With 6.5 digits this is not one of the ESR "indicator" kits. How low can you measure.
I use an analog meter, it goes upto 40 ohm ( but I made it non lineair for better resolution under 1 ohm, and accurate down to 100nF. But I think I change this and make it switchable between 1 ohm full scale and 40 ohm. ( not that this is important because if the meter corners it is good, the last cm on the scale is 1 Ohm so about 50 mOhm resolution) Fred PA4TIM Op 31 aug. 2011 om 18:40 heeft "tcxo" <tcxoe@...> het volgende geschreven: I typically end-up disconnecting each high-value aluminum electrolytic capacitor in order to test it. [Non-text portions of this message have been removed] |
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Re: Favorite bad capacitor debugging techniques?
Chris Moore
Hi,
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If they are in fact vertical mounted AXIAL caps, then you could cut one lead, test the cap, then solder the lead back together. Chris --- On Tue, 8/30/11, David Speck <Dave@...> wrote:
From: David Speck <Dave@...> Subject: [hp_agilent_equipment] Favorite bad capacitor debugging techniques? To: hp_agilent_equipment@... Date: Tuesday, August 30, 2011, 11:55 PM ? Looking over the list, I have noted that the majority of problems with old equipment is failure of the electrolytic capacitors in the power supplies over time. I wonder if the veterans can offer any suggestions on their favorite techniques for finding bad caps in circuit, especially those that have not been so considerate to have blown their end caps off or otherwise developed obvious physical failures. I have a critical undocumented circuit board of relatively recent construction with about 25 vertically mounted axial lead caps. It's begun eating fuses at an increasing rate, and now, even a 2 amp fuse blows instantly in a slot intended for a half amp fuse. No way to lift one lead of the cap without pulling it out of the PCB, with the attendant risk of ruining the irreplaceable board. (well, I could replace it for another $6-7,000, but that's not in the budget this week!) I figured I could put in another 2 amp fuse, and run it on a Variac at reduced voltage while watching the current consumption, and see what component heats up, but I really don't want to trash the microcomputer on the board. Any one have suggestions for any specific low voltage instruments for in-circuit cap checking, or home-brew gimmicks that one can work up, to give better information than the typical DVM and scope? Thanks in advance, Dave |
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Re: Replacement for 08565-60084 attenuator in HP 8565A...
Amos - you can use an external atten. to keep the input signal below +20
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dbm. Will In a message dated 8/31/2011 1:06:30 A.M. Pacific Daylight Time,
amosku@... writes: Hi all, With help from friends in this group, I have found the schematics in the manual, and I also identified the five missing parts in the HP 8565A that I cheaply bought from ebay. Now, I found it difficult to find a cheap source for 08565-60084 attenuator. Does any one know the replacement part for 08565-60084 (A34, RF attenuator) in HP 8565A? It does not seem to be easy to obtain this attenuator ($400). I wonder if anyone knows any information about this attenuator. If obtaining one is difficult, what options do I have? Also, I wonder if this attenuator is really needed to make the system work. Thanks in advance. Amos [Non-text portions of this message have been removed] |
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Re: Favorite bad capacitor debugging techniques?
J. Forster
Some years ago, I had a Brother FAX with a PS that died. I was damned if I
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was gonna pay well over $100 for a replacement PS. Of course, there were no prints to be had. I got pissed and sucked off every component and tested it. Turns out there was a 1 uF cap open. I got my revenge because I subsequently found several more, with exactly the same problem. A cap replacement fixed every one. Bottom line, get a Pace sucker if you do any PCB repair work. Best, -John ============== One thing I would never do is put in a bigger fuse. |
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Re: HP 204B Modifications.
2006. It's very straightforward.
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--- In hp_agilent_equipment@..., Glydeck <glydeck@...> wrote:
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Replacement for 08565-60084 attenuator in HP 8565A spectrum analyzer
Amos Ku
Hi all,
With help from friends in this group, I have found the schematics in the manual, and I also identified the five missing parts in the HP 8565A that I cheaply bought from ebay. Now, I found it difficult to find a cheap source for 08565-60084 attenuator. Does any one know the replacement part for 08565-60084 (A34, RF attenuator) in HP 8565A? It does not seem to be easy to obtain this attenuator ($400). I wonder if anyone knows any information about this attenuator. If obtaining one is difficult, what options do I have? Also, I wonder if this attenuator is really needed to make the system work. Thanks in advance. Amos |
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Re: Problems with HP8753C networkanalyzer
Jose V. Gavila
Hi Peter,
I went through a similar problem (not exactly the same, but the error was the same) and was able to fix it by an internal source auto-calibration. Please, check my WEB at for more information about what I did and the results. If you have any doubt, just ask :-) I hope it helps! Regards, JOSE At 09:54 31/08/2011, you wrote: hi group I have a HP8753C analyzer option 6 (6Ghz) that has a HP85047 testset. I get the following error when power on. No IF found check R input levelPhase lock lost when I se my display I have not strait line under 90Mhz. There is like noise on the line there. I did some tests in CW mode and se I loose my phase lock going under 87Mhz. Looking on the Cw signal with a spectrumanalyzer I se a very unstable signal. So when going below 87Mhz the display say Phase-lock lost. Going above make a stable frequency signal. Measurering the power out of the source (level set to 0dBm out say around -11dBm but that is after a loss of 6dB in a powersplitter (hp11667). so output od source is around -5dBm measured at 1Ghz. Level is flat over the range. What can be the root course for that problem. Best regards Peter Hansen OZ1LPR-- 73 EB5AGV - JOSE V. GAVILA - IM99sm La Canyada - Valencia(SPAIN) Radio and Test Equipment....... RadioRepair BLOG............... |
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Problems with HP8753C networkanalyzer
hi group I have a HP8753C analyzer option 6 (6Ghz) that has a HP85047 testset. I get the following error when power on. No IF found check R input levelPhase lock lost when I se my display I have not strait line under 90Mhz. There is like noise on the line there. I did some tests in CW mode and se I loose my phase lock going under 87Mhz. Looking on the Cw signal with a spectrumanalyzer I se a very unstable signal. So when going below 87Mhz the display say Phase-lock lost. Going above make a stable frequency signal. Measurering the power out of the source (level set to 0dBm out say around -11dBm but that is after a loss of 6dB in a powersplitter (hp11667). so output od source is around -5dBm measured at 1Ghz. Level is flat over the range. What can be the root course for that problem. Best regards Peter Hansen OZ1LPR
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HP 85662A Display power supply issue solved
Hello group ,
finally the problem has been solved, the cause was an 30.000?F completely dry, this capacitor named C4 in A23 was in the power supply of the RF section and not in the display section. [:)] the symptoms were not directly related to the RF section: i.e. the instrument Led N¡ã1 lit and not the second one, but the power supply in the display section was not OK with the voltmeter the voltages of the 15 V PS were +12V -12V and the 100V PS was only 60V in fact the open C4(30.000?F) elko in the rf section give a corrupted 5.2V Voltage that also corrupt(modulate) the display power supply 15V which in turn give false voltages to the other PS related to. Thanks for the help of the afficionados and Ham [:D] [Non-text portions of this message have been removed] |
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Re: Favorite bad capacitor debugging techniques?
One thing I would never do is put in a bigger fuse.
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A switcher might not start up using a lightbulb. Besides things allready named like following the current and looking for low voltages i do the following: If the instrument is still working I use my DVM to check DC levels and ripple uing the duall display ( but with a good DVM in the AC position is also possible) a el-cheapo meter will get confused by the mix of AC and DC especially if it is a switcher. And often to be ure I use a scope to look at ripple levels. If it is not working, I desolder caps and test them on DC leakage, capacitance and ESR. Diodes, resistors and tranistors I test in circuit if possible. This with a DVM and a tracker. I use a Pace Sucker, they are really great. But I'm no oldtimer ;-) Fred PA4TIM
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Re: Favorite bad capacitor debugging techniques?
zl2bkc
Dave,
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Based on your reference to having multiple vertical mounted caps I would assume you are talking about a SMPS. Personally I would not restrict yourself to the capacitors alone. Typically caps are the highest failure items, but based on my experience any resistor in the HV side is also a likely suspect, and if fuses blow then you need to check anything silicon along with GDT's and MOV's if they exist in circuit. The following reference is an extreemly comprehensive guide to repairing SMPS's - after reading it and applying its principles a few times I no longer fear SMPS's as I used to. In addition to the series light bulb trick, I suggest you disable the main switching transistor(s) by removal (and test when removed) to eliminate primary side or secondary side issues. PS. I highly recommend you invest in an ESR meter - even for the sake of eliminanation os any likely suspects. -- Wayne --- In hp_agilent_equipment@..., David Speck <Dave@...> wrote:
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Re: Favorite bad capacitor debugging techniques?
J. Forster
With good desoldering gear (likle a Pace solder sucker) you can pull parts
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with little risk, if you are careful. Otherwise, apply a current limited source to the power rails and check the voltage across each cap with a DMM. The lowest is your first suspect. -John =================== Looking over the list, I have noted that the majority of problems with |
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Re: Favorite bad capacitor debugging techniques?
Peter Gottlieb
As has been mentioned, the proper equipment makes a huge difference in parts replacement. If the board is that critical I would replace all the capacitors as a starting point, and check the diodes while you're at it. Depending on the capacitors, you may be able to break them up with a bit pair of dykes, carefully and avoiding any mechanical damage to the board. This will make lead removal much easier!
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On 8/30/2011 7:55 PM, David Speck wrote:
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Re: Favorite bad capacitor debugging techniques?
Tom Miller
Are you sure all the caps are installed the correct way? My experience has been that the aluminum electrolytic fail open or low capacitance and tantalums fail shorted.
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You could put a 100 watt light bulb in series with the line to limit the current then trace around to find what part of the supply is not coming up. Can you tell us a bit more about the board? What kind of power supply is it using, linear or switching/ Did you mean radial lead capacitors, both leads come out of the same end? Do you have soldering rework equipment available and someone that knows how to do the work? If it is an irreplaceable assembly, why not get someone skilled in that type of repair? But most important is to stop trying to run it with a higher current fuse. It was designed to use a 1/2 amp fuse and using a 2 amp fuse is asking for trouble. Do you have a DMM with the diode test feature? Can you get an ESR meter? Maybe it's not a bad capacitor. Regards, Tom ----- Original Message -----
From: David Speck To: hp_agilent_equipment@... Sent: Tuesday, August 30, 2011 7:55 PM Subject: [hp_agilent_equipment] Favorite bad capacitor debugging techniques? Looking over the list, I have noted that the majority of problems with old equipment is failure of the electrolytic capacitors in the power supplies over time. I wonder if the veterans can offer any suggestions on their favorite techniques for finding bad caps in circuit, especially those that have not been so considerate to have blown their end caps off or otherwise developed obvious physical failures. I have a critical undocumented circuit board of relatively recent construction with about 25 vertically mounted axial lead caps. It's begun eating fuses at an increasing rate, and now, even a 2 amp fuse blows instantly in a slot intended for a half amp fuse. No way to lift one lead of the cap without pulling it out of the PCB, with the attendant risk of ruining the irreplaceable board. (well, I could replace it for another $6-7,000, but that's not in the budget this week!) I figured I could put in another 2 amp fuse, and run it on a Variac at reduced voltage while watching the current consumption, and see what component heats up, but I really don't want to trash the microcomputer on the board. Any one have suggestions for any specific low voltage instruments for in-circuit cap checking, or home-brew gimmicks that one can work up, to give better information than the typical DVM and scope? Thanks in advance, Dave [Non-text portions of this message have been removed] |
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Re: Favorite bad capacitor debugging techniques?
David Speck wrote:
Hi. It sounds like you are doing a lot right already. The last instrument I was able to repair that had bad caps (and it had about a dozen of them!) was a Khron-Hite oscillator. The unit was not blowing fuses, and the caps did not show abuse, but the power supplies were at a very low output indicating they were trying to power short circuits. Here's what I did: Operate from a Variac to control how much current is flowing. Starting with an arbitrary reference point (I used the location where a PS wire came onto the main PCB) I put one lead of a high resolution VM at that point and then probed other PS points on the board with the other lead. You can map out the current flow on the board this way. When following a land the voltage drop will increase as you go away from the reference point until you come to a suspect component or a branch off of the land that goes to a suspect component. I was able to fairly quickly trace out voltage drops on the PS lands and find the shorted caps. Really nice to have my oscillator back - it was the only one I had that could do sub milli Hertz! Hope this helps! -- Bob Smither, Ph.D. Smither@... ======================================================================== "The most potent weapon of the oppressor is the mind of the oppressed." - Steven Biko ======================================================================== Circuit Concepts, Inc. 281-331-2744 |
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Favorite bad capacitor debugging techniques?
Looking over the list, I have noted that the majority of problems with old equipment is failure of the electrolytic capacitors in the power supplies over time.
I wonder if the veterans can offer any suggestions on their favorite techniques for finding bad caps in circuit, especially those that have not been so considerate to have blown their end caps off or otherwise developed obvious physical failures. I have a critical undocumented circuit board of relatively recent construction with about 25 vertically mounted axial lead caps. It's begun eating fuses at an increasing rate, and now, even a 2 amp fuse blows instantly in a slot intended for a half amp fuse. No way to lift one lead of the cap without pulling it out of the PCB, with the attendant risk of ruining the irreplaceable board. (well, I could replace it for another $6-7,000, but that's not in the budget this week!) I figured I could put in another 2 amp fuse, and run it on a Variac at reduced voltage while watching the current consumption, and see what component heats up, but I really don't want to trash the microcomputer on the board. Any one have suggestions for any specific low voltage instruments for in-circuit cap checking, or home-brew gimmicks that one can work up, to give better information than the typical DVM and scope? Thanks in advance, Dave |
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