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Thread: PYRAMID POWER SUPPLY

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  1. #1
    Join Date
    Oct 2001
    Location
    South Shore KY
    Posts
    485

    Default

    A BIG HOWDY!!! # I have this Pyramid Gold Series Model
    PS 36KX regulated DC Power supply, which has went south on me. #This is the second time. #First time the SCR shorted and I replaced it, problem fixed.. that was several years ago. #This time I was transmitting and it suddenly went into alarm. This time the SCR is not defective. #I replaced it anyway... #
    I have checked everything except the IC chips.. which I have no way of checking other than replacing them... #I was wondering if someone would have a parts list, or a troubleshooting guide for this power supply? #I have a schematic, but info on it is very limited. #No part numbers etc.
    Or maybe someone has had the same problem with a similar unit? #Any help will certainly be appreceiated.. Thank You. #
    #You may use my email to answer or post here. #My email is: #bennieh4@wmconnect.com ... # #
    B H Mineer
    KY Colonel

  2. #2

    Question

    Bennie -

    I found many Pyramid linear power supplies on "give-away" tables or in the trash barrels at hamfests. #They are a source for building your own linear power supplies. #They appear to have undersized heat sinks for the ratings advertised. Linear power supplies are straight forward to troubleshoot and repair. #I would suggest the following web sites:

    KBT DC Supplies (troubleshooting - they also do repairs)
    http://www.kbt-dc-supplies.com/index.php

    David Metz, WA0AUQ article [Power Supply construction]
    http://www.seits.org/features/pwrsup.htm

    Schematic
    http://www.seits.org/features/pwrsup.gif

    w9gb




  3. #3
    Join Date
    Oct 2001
    Location
    South Shore KY
    Posts
    485

    Default

    This Power supply is regulated Supply (protected for over voltage and for too much current draw) therin lies the problem.. It is in shut down condition. Taking all load off, it is supposed to reset itself, it does not. So seems to me there is something wrong in the shutdown circuit. There are two 14 pin IC"s in there that I have no information on. Not knowing what is inside makes it extremely difficult to troubleshoot. I have many years experience in the tv and radio repair field, but need help on this. I could of course rebuild it and make it a linear supply, but don't wish to do that if, I can find some way to fix it first. Thanks...
    B H Mineer
    KY Colonel

  4. #4

    Question

    B H -

    Your Pyramid power supply uses the popular LM 723 voltage regulator chip (a proven IC and over 25 years since first released). #I am surprised you have not come across this popular IC in the radio/TV repair business
    #
    The KBT DC web site has all of the specification sheets on the LM 723 voltage regulator IC as well as the 2N3055 or 2N3771 pass transistors. #I provided the spec sheets - so that they would be available for easy reference

    Repair tutorial number 1
    http://www.kbt-dc-supplies.com/fixem1.php

    Repair tutorial number 2
    http://www.kbt-dc-supplies.com/fixem2.php

    Pyramid does not answer e-mails and I am not aware of "on-line" schematic sources - other than this one diagram. The Pyramid PS-52KX manual can be found here. #
    http://www.cbtricks.com/miscell...._om.pdf

    The KBT web site has over 30 pages of information on the repair of linear power supplies using common IC regulators and pass transistors (e.g. Pyramid, Astron, TrippLite) -- better than a SAMS PhotoFact.

    Greg
    w9gb

    BTW
    KB7KBT has been able to "walk" many amatuer radio operators with little experience through the repair process. #Just drop kb7kbt an eMail, tell him what you have and what you think might be the problem.
    kb7kbt@gfmdesigns.com

    All power supplies need to be sent to KBT postage paid and insured round trip. Repair fees will consist of parts, plus a flat fee of $25. #You can then put their "Life Time Warranty" to work.




  5. #5
    Join Date
    Jul 2003
    Posts
    1,329

    Default

    This does not answer the above question, but I have a couple of damaged supplies (not Astron) which I ran through the dishwasher after a house fire.

    I discovered, and ordered one each regulator board from Astron for their RS20 and RS35 supplies, $20.00 USD each plus a little shipping.

  6. #6
    Join Date
    Jun 2003
    Location
    Fall City, WA
    Posts
    2,593

    Default

    Check the zener in the crowbar circuit.
    If it shorted, it would explain all..

  7. #7
    Join Date
    Oct 2001
    Location
    South Shore KY
    Posts
    485

    Red face

    > I am surprised you have not come across this popular IC in the radio/TV repair business < Truth is I have come across this IC many times, but this one is not marked as such.
    It has a couple of circled plus signs and number 609A on it.
    Many thanks for all the helpful info. I got a schematic from one of the urls that you provided and checked the circuitry looks to be the same as mine. So I ordered the IC and will install it to see what happens. Will post the results later. agn, thanks.
    B H Mineer
    KY Colonel

  8. #8

    Smile

    B H -

    Let us know of your results. #
    Too much "off-brand" labeling in equipment these days.

    WD7WHQ mentioned to check the 15 volt zener diode (a good idea).
    http://www.kbt-dc-supplies.com/crowbar.php

    The zener diode monitors the output voltage of the power supply. When the voltage gets to 15 volts, the Zener diode conducts. #This in turn fires the SCR and therefore short circuits the output of the supply. Eventually draws enough current to trip the breaker or "blow" the AC input fuse.

    Greg
    w9gb




  9. #9
    Join Date
    Oct 2001
    Location
    South Shore KY
    Posts
    485

    Default

    # To all who replied, many thanks. #Here is what the problem was: #The four output transistors went south. #None were shorted, and this wasn't caused by an overload, They probably got too hot. #
    The problem as I see it is this: #The thermal heatsink compound had dried up, and was not conducting heat from the transistors to the heat sink. #I bet a lot of other users of
    power supplies like this have the same problem. #Anyhow replacing them and applying a liberal amount of new compound
    fixed the problem. #It is now in fine working condition. #P.S. I bet the manufacturers did that on purpose, applying a real small amount of compound and hoping it will last till the item is out of warranty, and then, sell a new one, or charge a lot to repair them?.... HAW!!! # #
    B H Mineer
    KY Colonel

  10. #10
    Join Date
    Jan 2000
    Location
    Indiana
    Posts
    4,922

    Default

    TR: It does not take a lot of the conductive grease to make an adequate transfer material. A thin layer on either one, then assemble.

    By the way, this stuff is bad news. Make sure you clean your hands, discarding the paper towel (or whatever you used). Then wash liberally. Dow Heat Sink compound is on the list of "bad things" to be around.

    After the transistors are bolted to the heat sink, take a paper towel and wipe off the edges of the transistors to get rid of the excess.

    73

    Bill, W0LPQ

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