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RM HLA300 low power output.

Discussion in 'Amplifiers' started by Stuuk, Jun 10, 2012.

  1. Stuuk

    Stuuk Member

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    Hi All
    New member here.

    I've just acquired an RM HLA300 Solid state Amplifier but it needs a little sorting out. I'm hoping someone on here has worked on these.

    Its a revision 1.10 circuit board and has the 3 fans mounted on the heatsink.



    The main problem is the amp only seems to be putting out a max of 190watts pep ssb with 20watts drive ie less than half power.

    I've lifted the base terminal on each of the 4 sd1446 power transistors and can do a standard junction test between the base-emitter and base-collector and the transistors all seem to check ok.

    Can anyone with some experience of these amps give me some troubleshooting pointers?

    Also noticed when transmitting that occasionally getting a beep beep beep from the amp which i think means out of tune or over heating (The translated manual isnt that clear on the audio codes).
    I was transmitting on 40m and had 40m selected and had the antenna tuned for 1:1 swr. Funny thing is when I set the amp to auto and the amp auto selected 40M I didnt seem to get the beep but this might be a coincidence.

    I have the bottom cover off while testing and nothing seems to be getting too hot not even really warm.

    Any help would be much appreciated

    Stu
     
    #1
  2. dd18

    dd18 Davo

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    hla300

    Those amps are really touchy.
    What is it putting out with 5w input?
    Put it on a dummy load and check it over the bands.
    Don't use the auto setting for the tests.
    Go over and resolder all the connections in the filter assembly esp the 40m ones.
    If there is a big descrepancy between the bands then the filter is the place to start.
    20w is a bit high on input side for these amps.
    They were made for the FT817 and work best with 5w PEP input.
    Should be good for 250-300w pep out with 5w pep in.
     
    #2
  3. Stuuk

    Stuuk Member

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    Ok thanks for the info
    I'll do the tests you suggested across the bands

    Did a bit more testing after my last post and one pair of sd1446's is getting a bit warmer than the other pair

    The 2 nearest the case end stay relatively cool to the touch after a lengthy test transmission and the other pair are warm to the touch but not what i would describe as hot

    Cheers

    Stu
     
    #3
  4. Stuuk

    Stuuk Member

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    ps
    5w input is only putting out about 100watts
     
    #4
  5. ExitThirteen

    ExitThirteen Grumpy, Cranky Repairman

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    Does it look like any resistors are showing signs of getting hot or burnt? Best place to look is on the input and output combiners, and see if those resistors show any signs of getting hot. Could also look to see if the biasing resistors may have gotten hot also. Let us know how you get on.



    ~Cheers~
     
    #5
  6. Stuuk

    Stuuk Member

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    R37 next to TR16 looks like it has been getting hot at some stage but its still measuring appx 68r

    Cheers

    Stu
     
    #6
  7. Stuuk

    Stuuk Member

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    Not sure if this is significant but neither jmp1 or jmp2 have any bridging clips on them

    I know jmp2 is the ptt sense either ground or +ve activated but not sure what jmp1 is for.

    Also both trim pots are straight up and down both in the centre of their travel
     
    #7
  8. trucker

    trucker Active Member

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    I have read somewhere that the rated outputs on the RM Italy amps are a bit generous.
    And as has been mentioned, driving it with 20 watts is over-driving it. They are supposed to be driven with 5-10 watts max. I've been thinking of getting an HLA-300 and had one lined up but, due to communications problems between me and the seller, i missed out on it.
    Good luck.
    trucker
     
    #8
  9. TonyV225

    TonyV225 Supporting Member

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    Im willing to bet that it got hot when driving it with 20 watts I agree and say pay close attention to the input section and when straightened out drive it with 10 i 12 watts input it will trun cooler stay cleaner and the power you would be lacking compared to the 20 watts in isnt even going to be noticable on the other end.

    I know the SD-1446 transistors should easily handle 20 watts input but the rest of the resistors and parts used Im not sure about.RM Italy has come a long way and makes a great product but they do have to be run differently and to RM Italy specs.
     
    #9
  10. Stuuk

    Stuuk Member

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    Ok I found something
    It looks as though someone has replaced R12 and R56 at some stage
    These are part of the input network around the attenuator relay.

    They are both supposed to be 68R according to the parts list but they have been replaced with 80R resistors.
    Furthermore the resistors look suspiciously like wire wound ones to me which can't be right for RF input can it?

    I'll get some 68R 5 watt carbons and replace them

    Cheers

    Stu
     
    #10
  11. kc8adu

    kc8adu Active Member

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    post a pic.
    wirewounds are a big no no with rf.
    and if you can lift b and c on all 4 transistors to check them with a real tester like my sencore super cricket you may find one or more damaged.1446's are relatively high gain parts and do not need a lot of drive.probable damaged one or more.
     
    #11
  12. Stuuk

    Stuuk Member

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    I replaced the wire wounds with carbon and there is a slight improvement but not much.

    I've already lifted the base on each transistor and the b-c and b-e junctions pass the forward and reverse voltage test.

    I dont have a tester that will check gain etc
     
    #12
  13. dd18

    dd18 Davo

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    Power meter readings

    Are you reading the power with a proper PEP meter?
    If one set of transistors is running hotter than the others then something is possibly not right somewhere. Perhaps the transistors have been replaced at sometime and are not properly matched.
    What frequency are you making the readings on?
    I stopped importing these because they were too easy to abuse. Keep the input power down and they work very well but they are a little susceptible to swr and RF..but they do perform well when they work. Recently RM did make a few modifications to the board to improve stability and are now well past ver1.1

    I assume you have the Hi/lo switch set on high?

    rgds,
    Dave
     
    #13
  14. Stuuk

    Stuuk Member

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    Hi
    Thanks for the response

    Ok have found someting else

    I did a cw keydown test about 7w in and 100 watts out
    The sd1446's started getting warm to the touch but not hot
    After about 10 seconds R37 was visibly getting very hot and started to smell

    So need to work out why r37 is passing a lot of current

    Schematic here if anyone cares to take a look
    http://www.rmitaly.com/download/manuals/HLA300-manual_rel_110.pdf

    Stu
     
    #14
  15. Robb

    Robb Yup

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    So you tested those transistors that resistor is feeding?
     
    #15
    Last edited: Jun 12, 2012

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