Re: Replacement for 08565-60084 attenuator in HP 8565A...
Will,
Yeah. I have thought about this option too. But that means I have to give up the ability to internally choose attenuation.
Right now, I am facing the issue of choosing the cable that go between the RF connector and the coax switch (K2). No experience on choosing or specifying one before.....
Amos
________________________________
From: "w0eom@..." <w0eom@...>
To: hp_agilent_equipment@...
Sent: Wednesday, August 31, 2011 8:50 AM
Subject: Re: [hp_agilent_equipment] Replacement for 08565-60084 attenuator in HP 8565A...
?
Amos - you can use an external atten. to keep the input signal below +20
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]
[Non-text portions of this message have been removed]
|
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
tool. A short and a good cap both have a low ESR!
-John
===============
----- 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@...
[Non-text portions of this message have been removed]
|
Re: Favorite bad capacitor debugging techniques?
If a capacitor is pulling a bus down, an ESR meter is really not the right
tool. A short and a good cap both have a low ESR!
-John
===============
toggle quoted message
Show quoted text
----- 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@...
|
Re: Favorite bad capacitor debugging techniques?
toggle quoted message
Show quoted text
----- 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@...
|
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.
Here's an example of my "Before" and "After" measurements of an aluminum electrolytic cap that was used in the switch-mode power supply of an instrument:
Symptom: Unit will no longer switch from ¡°Standby¡± to ¡°On¡± mode.
Failed 1000uF 10VDC electrolytic cap on power supply board
Bad Hong (Chinese) cap, 2 years old
Test Freq.
Capacitance
D
ESR
120 Hz
391 uF
3.58
12.04 ohms
1 kHz
154.3 uF
10.6
10.88 ohms
10 kHz
23.2 uF
14.1
9.88 ohms
Replacement Cap measured
Test Freq.
Capacitance
D
ESR
120 Hz
1001 uF
0.071
0.000093 ohm
1 kHz
952 uF
0.344
0.000057 ohm
10 kHz
855 uF
0.326
0.000051 ohm
Luckily most aluminum electrolytics HP used in the "good old days" seem to have lasted for several decades - but as you know, are finally beginning to fail in some circuits, especially where near higher temperatures.
By comparison, some Chinese brands of aluminum electrolytic caps (produced during the last 10 years) are failing much sooner, e.g., something like 2 to 6 years of use.
Google "capacitor plague" for more information about that problem.
-Greg
[Non-text portions of this message have been removed]
[Non-text portions of this message have been removed]
|
Re: Favorite bad capacitor debugging techniques?
Hi,
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
toggle quoted message
Show quoted text
--- 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
|
Re: Replacement for 08565-60084 attenuator in HP 8565A...
Amos - you can use an external atten. to keep the input signal below +20
dbm.
Will
toggle quoted message
Show quoted text
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]
|
Re: Favorite bad capacitor debugging techniques?
Some years ago, I had a Brother FAX with a PS that died. I was damned if I
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
==============
toggle quoted message
Show quoted text
One thing I would never do is put in a bigger fuse.
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
----- 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
|
Re: HP 204B Modifications.
2006. It's very straightforward.
toggle quoted message
Show quoted text
--- In hp_agilent_equipment@..., Glydeck <glydeck@...> wrote:
Jeanette,
I had heard that as well. Do you remember what year the audio express article was published?
George
On Aug 30, 2011, at 7:26 AM, "Jeanette" <jdwalton@...> wrote:
There was such a modification in June and July issues of AudioXpress (which, I am going to guess, you don't have!). Uses a pair of 1N4742 12V 1W zeners to split the supply.
There's an important utility to running the oscillator off batteries -- you're going to get a much lower noise floor and no pesky 60, 120, 180Hz power supply artifacts. You can rebuild the battery packs with Nicads, or button cells and use the existing charge circuit, or use one of the intelligent charger chips from, for instance Texas Instruments (Unitrode.)
I rebuilt the battery pack of my HP3581 wave analyzer -- and it was worth the investment.
--- In hp_agilent_equipment@..., "willcoele@" <willcoele@> wrote:
I have three 204B oscillators I'm restoring. One had a problem where C2 (the 3 section, 1% capacitor) had a shorted section. I replaced the shorted section with single 1%, .3uF. Close enough for the Government!
My problem is, I'm converting the battery units to AC. It has a transformer a bridge rectifier and some filtering but secondary of the transformer isn't center tapped and it's not referenced to ground. I used a 7812 and a 7915 regulator to provide the +/- 12volts but when I wired it to the transformer the plus side dropped to 5.6 volts and the minus side was 37.6 volts. The plus side was drawing more current than the minus side. To balance it out I used a 15v Zener diode on the minus side and the plus side increased to 25.75 volts.
It appeared to be working but when the frequency was set to 250to 1KHz, there was a small amount ripple on the + 12v. To reduce the ripple, I used a 1000uF electrolytic on the +12v side.
Has anyone done a similar modification? Is there a better way?
|
Replacement for 08565-60084 attenuator in HP 8565A spectrum analyzer
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
|
Re: Problems with HP8753C networkanalyzer
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...............
|
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
|
Photos of the HP 85662A measurments
The photos taken during the search has been uploaded in the photos
section (on1ev)
cheers [:)]
|
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]
|
Re: Favorite bad capacitor debugging techniques?
One thing I would never do is put in a bigger fuse.
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
toggle quoted message
Show quoted text
----- 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]
|
Re: Favorite bad capacitor debugging techniques?
Dave,
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
toggle quoted message
Show quoted text
--- In hp_agilent_equipment@..., David Speck <Dave@...> wrote:
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
|
Re: Favorite bad capacitor debugging techniques?
With good desoldering gear (likle a Pace solder sucker) you can pull parts
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
===================
toggle quoted message
Show quoted text
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
|
Re: Favorite bad capacitor debugging techniques?
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!
toggle quoted message
Show quoted text
On 8/30/2011 7:55 PM, David Speck wrote:
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: Favorite bad capacitor debugging techniques?
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.
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
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----- 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:
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? 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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