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Comparing transistors - IC-71A

Discussion in 'General Technical Questions and Answers' started by KD0CAC, Sep 11, 2017.

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  1. KD0CAC

    KD0CAC Ham Member QRZ Page

    Got a donation for our club , a Icom IC-71A
    Last owner said ,
    It was known not to work , last working had some hum .
    Sat for a long time , no not working .
    Took home and opened up to look for any obvious stuff , also looked on web for common issues .
    Found one of the main common issues was the loss of memory / programing with dead battery , found a replacement board with non volatile memory .
    While looking over most of the boards , I found [ do not remember what board it is called , but as you look at front , it is mounted on the right side , a vertical board ] I saw signs of a couple components had blown / flash marks on board & surrounding parts , had been replaced .
    2 transistors that the repair manual show as Q3 2SA1048Y , Q4 2SC2448GR
    The marks on the replacement units are both SK125 YS , so both the same , unlike the originals being 2 different ?
    Also found a broken wire from board to antenna ground at panel mount .
    So I am not sure if these SK transistors can be used ?
    Personally , I would have cleaned all residue from old blown parts removed ;)
     
  2. KA9JLM

    KA9JLM Ham Member QRZ Page

    The SK125 will NOT be a sub for both, Because 1 of the the originals is NPN and the other is PNP.

    Good Luck.
     
  3. G4COE

    G4COE Ham Member QRZ Page

    2SA1048Y data sheet
    2SC2448 datasheet

    The 2SA1048 is a 50Vcb max at 150mA and a pd of 0.2 Watts
    The 2SC2448 is a 650Vcb max at 7 Amps and a pd of 80 Watts

    You sure would see fireworks sticking the wrong ones in..... best bet is either use the correct ones or look for cross references, in many cases transistors are graded by the manufacture, many may contain a batch number or a date code when the device was made.


    Dave
     
    KA9JLM likes this.
  4. KA9JLM

    KA9JLM Ham Member QRZ Page

    With the TO case being different, Getting them mixed up would be hard.

    I would double check and make sure you are looking at the correct part on the board.
     
  5. WB2LBV

    WB2LBV Ham Member QRZ Page

    Does it power up? Have you checked the power supply, that is always the first place to start. The supplies in the R71A and R7000 are known to be crappy and hot-running, make sure it's putting out good voltage without hum. If the supply is suspect or definitely bad try running it on an external 12V supply (it's designed to do that). There's an internal molex you disconnect and the 12V goes into that.
    Go through the whole unit for bad solder connections paying particular attention to the inline connectors and active stuff on heat sinks.
     
    K0OKS likes this.
  6. KD0CAC

    KD0CAC Ham Member QRZ Page

    Thanks for the replies , this will probably end up as a parts source .
     
  7. WB2LBV

    WB2LBV Ham Member QRZ Page

    Don't trash it unless it's really a basket case. If it's above your skill level to troubleshoot and fix (or write off), get it to someone who can deal with it. These are still excellent receivers that have value (even if there isn't as much to listen to these days).
     
  8. KD0CAC

    KD0CAC Ham Member QRZ Page

    It's a club donation , so what ever is offered at the next ham fest .
    Again it was donated in this condition to the club - belongs to club .
    With a lack of history , multiple issues and not mine , its a matter of what a buyer values at ?
    I have too many of my own projects and not enough funds to just play .
     
  9. KA9JLM

    KA9JLM Ham Member QRZ Page

    So you have a club and none of the members can repair a radio ?

    Or the club does not have the funds to buy $3 in parts ?
     
  10. KD0CAC

    KD0CAC Ham Member QRZ Page

    Too negative of a response to reply to , oh well ;)
    You may not have read the posts , multiple issues at least $125 in parts AND THAT'S TO SEE IF THERE ARE OTHER ISSUES ?
    Our club get a lot of donations every yr. , all but 10% of moneys from sales are sent to the ARRL defense - http://www.arrl.org/spectrum-defense-fund
    I do not get hands on everything the clubs gets in donations , but I would say at least 30% has some kind of damage , malfunction etc.
    And it is an opportunity for buyer to get a good deal , most of our sales are below the average ham-fest pricing and everyone but you
     

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