HP8920B Power supply capacitors??
¿ªÔÆÌåÓýHi? From my experience switch mode power supplies require 50% load on the Maine supply? usually the 5 volt supply for them to work properly on the other rails ? From:
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On Behalf Of RFI-EMI-GUY ? I guess I will take a look and see what I can find. Does anyone know if the PS can be voltage tested outside the unit without load? No virus found in this message. |
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On 10/4/19 5:34 PM, Paul Bicknell wrote:
From my experience switch mode power supplies require 50% load on theBe careful here, some switching power supplies require a load and some don't. Most very early ones (meaning WAY earlier than the HP 8920) do, while essentially nothing newer does. My rule of thumb has the dividing line falling around the early to mid 1980s, but it varies depending on who made it. -Dave -- Dave McGuire, AK4HZ New Kensington, PA |
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Hi I can only afford Old HP equipment
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Paul -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Dave McGuire Sent: 04 October 2019 22:41 To: [email protected] Subject: Re: [HP-Agilent-Keysight-equipment] HP8920B Power supply capacitors?? On 10/4/19 5:34 PM, Paul Bicknell wrote: From my experience switch mode power supplies require 50% load on theBe careful here, some switching power supplies require a load and some don't. Most very early ones (meaning WAY earlier than the HP 8920) do, while essentially nothing newer does. My rule of thumb has the dividing line falling around the early to mid 1980s, but it varies depending on who made it. -Dave -- Dave McGuire, AK4HZ New Kensington, PA ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2016.0.8048 / Virus Database: 4793/15886 - Release Date: 08/14/18 Internal Virus Database is out of date. |
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By "old" in the context of switching regulators I mean 1960s and
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1970s. Most stuff from the 80s on does not require a load for proper regulation. There are exceptions, of course. -Dave On 10/4/19 5:56 PM, Paul Bicknell wrote:
Hi I can only afford Old HP equipment --
Dave McGuire, AK4HZ New Kensington, PA |
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By old I mean I mean 1960s and 1970s.
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OK actually HP 9000 computers Best regards Paul -----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Dave McGuire Sent: 04 October 2019 22:59 To: [email protected] Subject: Re: [HP-Agilent-Keysight-equipment] HP8920B Power supply capacitors?? By "old" in the context of switching regulators I mean 1960s and 1970s. Most stuff from the 80s on does not require a load for proper regulation. There are exceptions, of course. -Dave On 10/4/19 5:56 PM, Paul Bicknell wrote: Hi I can only afford Old HP equipment -- Dave McGuire, AK4HZ New Kensington, PA ----- No virus found in this message. Checked by AVG - www.avg.com Version: 2016.0.8048 / Virus Database: 4793/15886 - Release Date: 08/14/18 Internal Virus Database is out of date. |
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UPDATE
Well; I took the HP 8920B apart this weekend. It has the same power supply as pictured here (photo from e-bay listing). This also appears to be same as the schematics kindly provided by Ron Wilkinson earlier in this thread. Weird; I turned the unit on with the covers off and could smell none of the odor I detected before. It was behaving.? I was hoping to see a bit of smoke or a part overheated. I used an UV lamp to see if I could detect any electrolyte leakage, did not see anything, though I don't know if this would work. With the PS still installed I could observe most of the components in the 120V switcher circuit from the edge (bottom) and I used an IR thermometer to check temperatures after about an hour. This was done at room temp 73F and I found that the hot spots were: T1 127F - at top of core Q1 116F - main switcher C7 113F - a Rifa capacitor .047 630V J5? 105F - CORCOM input filter. This seems to heat quickly. L1 106F - Input choke L2 , C5 and C6 103F - Output of rectifier Most of the heat is on the side of the transformer closest to mains. Partly because of IR drop of parts and mostly the fan air circulation seems to ignore this side of the board, at least with covers off. I was hoping to see a part with obvious distress but none was spotted. I remain suspicious of the Rifa capacitor C7 and the bulk filters C5 and C6 . Those two look fine, however the end of the capacitors where the pressure relief exists are covered with a plastic disc so if they vent slightly, that may be unnoticed. Their is a 10 ohm NTC inrush thermistor RT1 that could be making a puff of heat when it responds. I did see some silicon glue near it (forgot to remove) that may be getting singed. I could not get a temp from this part or the rectifier near it. I am going to order a crash kit of parts so that next time I can do surgery. I have read that some capacitors are "self healing" . I don't know if that applies, nor how many times they can heal. I think my Monitor is a a 1998-1999 vintage I bought used in DEC 2002. Since then its use has been very light a few hundred hour a year at most. When received It had some light screen burn in, no dust inside and had the odor from the beginning. |
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Marc;
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Would you by chance have a copy of your parts order so I can order the same set of caps for mine?? Also if you can point out C63 and C65 in the photo above or the schematic, I would be much obliged. Joe On Mon, Sep 30, 2019 at 02:23 AM, marcschrdrs wrote: I had a 8920A recently on the bench with "magic smoke" issues: suspected RIFA X2 issues from the smell. |
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Thanks, that is good to know as I could use a current limited DC supply while testing unloaded. On Wed, Oct 16, 2019 at 03:03 PM, Robert G8RPI wrote:
Hi, |
RFI-EMI-GUY
Paul Bicknell
Dave McGuire
