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Thread: Astron RS 50M power supply problem

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  1. #1

    Default Astron RS 50M power supply problem

    Hello; I have had a short circuit accident with this power supply. A wire had touched the lower 1N1184A diode to ground. The 1N1184A tested ok. So far I found a blown power transistor 2n3771 on the back. That one was easy because it unplugged for testing. Can someone look up the schematic and walk through the circuit and tell me what other components may have blown? It would save time from me un-soldering parts just to test them. I am not that good with switching power supply theory. Thank you.

  2. #2

    Thumbs up

    Quote Originally Posted by n2mir
    Can someone look up the schematic and walk through the circuit and tell me what other components may have blown?
    It would save time from me un-soldering parts just to test them. I am not that good with switching power supply theory.
    The Astron RS-50M is NOT a Switch-Mode Power Supply (SMPS) ... it is a LINEAR Design Power Supply (heavy EI transformer).

    PRIMER - Regulated Linear Power Supply Construction, What's inside your Astron®?
    David Metz, WA0AUQ
    http://www.repeater-builder.com/astr...on-article.pdf

    Repeater Builders Techncial Informaiton Page (RBTIP) has EVRYTHING you need to troubleshoot and repair this specific Astron model.
    http://www.repeater-builder.com/rbtip/

    READ this SECTION FIRST
    Introductory Information on Astron™ power supplies
    http://www.repeater-builder.com/astr...tro-stuff.html

    Schematics and service information on Astron™ power supplies
    http://www.repeater-builder.com/astr...ron-index.html

    ==
    w9gb
    Nullius in verba

  3. #3

    Default

    Quote Originally Posted by W9GB View Post
    The Astron RS-50M is NOT a Switch-Mode Power Supply (SMPS) ... it is a LINEAR Design Power Supply (heavy EI transformer).

    PRIMER - Regulated Linear Power Supply Construction, What's inside your Astron®?
    David Metz, WA0AUQ
    http://www.repeater-builder.com/astr...on-article.pdf

    Repeater Builders Techncial Informaiton Page (RBTIP) has EVRYTHING you need to troubleshoot and repair this specific Astron model.
    http://www.repeater-builder.com/rbtip/

    READ this SECTION FIRST
    Introductory Information on Astron™ power supplies
    http://www.repeater-builder.com/astr...tro-stuff.html

    Schematics and service information on Astron™ power supplies
    http://www.repeater-builder.com/astr...ron-index.html

    ==
    w9gb
    When I bought this power supply 22 yrs ago I was told in the catalog that it was a switching supply. There are 4 each 2n3771 with a 5th mounted on the back. I have attached the schematic. The positive side 1n1184A was the one that got shorted out. I just need to know what might have blown elsewhere from the 2n3771 mounted on the back?
    Attached Files Attached Files

  4. #4

    Default

    Quote Originally Posted by N2MIR View Post
    Hello; I have had a short circuit accident with this power supply. A wire had touched the lower 1N1184A diode to ground. The 1N1184A tested ok. So far I found a blown power transistor 2n3771 on the back. That one was easy because it unplugged for testing. Can someone look up the schematic and walk through the circuit and tell me what other components may have blown? It would save time from me un-soldering parts just to test them. I am not that good with switching power supply theory. Thank you.
    Ok, I looked at the back label. It says 37amp continous and 50 amp interminten cycle. I am reading the articles you put on here. Thank you so much!

  5. #5

    Default

    If you can afford it There is a ham selling an "Upgrade regulator board".

    Over the years the Astron was "Revised" numerous times to correct for minor problems such as RF blowing the regulator IC etc and it gets hard to find the correct schematic.

    Since you blew one of the 2n3771 it is recommended/best to replace all 4 since they are in parallel.....
    I thought I could get rich in the stock market by investing in
    Viagra, Geritol, And Ginseng but my stocks didn't rise to the occasion.
    Hell, I figured that there was always somebody somewhere either trying to
    Get it up
    Get it going
    or
    Trying to remember what to do with it.
    73 De Bubba
    [COLOR=#0000CD]4 out of 5 Seniors prefer the taste of
    ALPO over other leading National Brands
    [/COLOR]

  6. #6

    Post

    Quote Originally Posted by kd8dey
    If you can afford it. There is a ham selling an "Upgrade regulator board".
    Bubba -

    That is Skipp May. He is no longer selling these boards (and does not answer e-mail queries for them)
    He can be found on the Repeater Builders mail reflector -- addition of a few key components can accomplish same results as his board.
    This is outlined at RBTIP (Information there) and can be DIY performed cheaply.

    Quote Originally Posted by n2mir
    When I bought this power supply 22 yrs ago, I was told in the catalog that it was a switching supply.
    It is NOT a Switch Mode Power Supply (SMPS) which are lightweight = 10 lbs,
    it is a Linear Supply (EI transformer) which are heavy = 46 lbs, and use the LM723 regulator and 2N3711 NPN pass transistors.

    Most likely a misprint in that catalog 22 years ago =OR= a mis-understanding on your part.
    BTW, Astron does NOT make or sell SMPS rated at 50 Amps !!

    HERE is the ASTRON Product Page for Linear Power Supplies
    http://www.astroncorp.com/linear.shtml

    Quote Originally Posted by n2mir
    There are 4 each 2N3771 with a 5th transistor mounted on the back panel.
    CORRECT, these 4, 2N3771 on heat sinks are the NPN pass transistors to handle the high current ratings (50 amps) for this supply.
    The 5th one (2N3771) is Q100 a driver transistor that can handle the switching current (LM723 regulator is only rated to 100 mA).
    These NPN transistors can FAIL, either as OPEN or SHORTED.

    They have to be TESTED individually with a VOM (analog meter) or a DVM (digital readout).
    The testing procedurtes are DIFFERENT, depending on the meter that you are using !!

    I have attached the schematic. The positive side 1N1184A was the one that got shorted out.
    YES, the 1N1184A is the Power Silicon Rectifier Diode (there are 2 of them), rated at 40 Amps each in a DO-5 stud case.
    These serve as the MAIN rectifier for the output voltage.
    http://www.vishay.com/docs/93492/1n1183.pdf

    I just need to know what might have blown elsewhere in the supply
    other than the Four (4) 2N3771 transistors on the heat sinks.
    The 2N3771 transistors mounted (on the heatsinks) are the pass transistors in direct line to the stud rectifier (1N1184A) you shorted.

    The 2N3771 on the rear panel is Q100 .. it is used as a DRIVER from the LM723 regulator.
    IF you were lucky .. it is OK. IF Q100 is BAD (Shorted or Open) ... then you may also have a BAD LM723 regulator.

    w9gb
    Last edited by W9GB; 01-17-2012 at 11:41 PM.
    Nullius in verba

  7. #7

    Default

    Wish I was close enough to take a look. Would be a fun repair project.
    I thought I could get rich in the stock market by investing in
    Viagra, Geritol, And Ginseng but my stocks didn't rise to the occasion.
    Hell, I figured that there was always somebody somewhere either trying to
    Get it up
    Get it going
    or
    Trying to remember what to do with it.
    73 De Bubba
    [COLOR=#0000CD]4 out of 5 Seniors prefer the taste of
    ALPO over other leading National Brands
    [/COLOR]

  8. #8

    Default

    Quote Originally Posted by W9GB View Post
    B
    i

    CORRECT, these 4, 2N3771 on heat sinks are the NPN pass transistors to handle the high current ratings (50 amps) for this supply.
    The 5th one (2N3771) is Q100 a driver transistor that can handle the switching current (LM723 regulator is only rated to 100 mA).
    These NPN transistors can FAIL, either as OPEN or SHORTED.

    w9gb

    Actually, the "5th" 2N3771 drives the pass transistors (four 2N3771's) but there's also a TIP29 transistor that provides drive from the 723 regulator IC to the single 2N3771. (A 2N3771 alone doesn't have sufficient gain to be able provide sufficient drive to push four 2N3771's to pass up to 50 Amperes!) That TIP29 transistor should also be checked.

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