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Sencore SG-165

Discussion in 'DIY' started by RocketMonkey, Apr 1, 2017.

  1. RocketMonkey

    RocketMonkey Active Member

    Messages:
    255
    Location:
    Kansas city area
    I just got a new boat anchor. Most of it seems to work thus far. However the left channel transformer is burned up and shorted out. Any ideas other that the obvious buy a donor for a transformer? Any traps with these things I need to look out for? I already see a couple crusty caps so working or no I'm sure it could use a once over. If it ain't broke, fix it anyway right?

    20170331_205251.jpg
     
  2. loudnoises

    loudnoises Escalates Quickly Subscriber

    Messages:
    867
    Location:
    Pondside, NH
    Pretty sure that's one of the preferred tools for tuner alignment. Quite jealous.

    I'm going to selfishly recommend a full refurb so i can then use it as a tutorial to do the same.

    :lurk:(while i wait for the adults to arrive)
     
  3. ConradH

    ConradH AK Subscriber Subscriber

    Messages:
    6,843
    Location:
    Canandaigua, NY
    They all need a refurb and are a royal PITA to work on. That said, they do a decent job for most alignments. The THD is a bit high, but it will still get the job done on all but TOTL tuners. I never use the meters or power functions, just the RF stuff, so having a bad transformer wouldn't be much of an issue. The output pad is a bit weird and unobtainable, but can be subbed with a low value pot, 75 or 100 ohms, if bad. FWIW, I never wanted to open mine again, so replaced almost every cap with carefully derated tantalums. There are also a few big electrolytics that should be replaced. There's a silkscreen error on the power supply board and maybe elsewhere, depending on vintage. Lots of info and discussion over at antiqueradios.com in the test equipment section. Do you have any probes or cables? Not hard to make if you don't.
     
  4. RocketMonkey

    RocketMonkey Active Member

    Messages:
    255
    Location:
    Kansas city area
    I bought it mostly for the stereo modulation and IF sweep. Im planing on learning to do FM alignments. Ive got some basic cables and what not. Still need more odds and ends. Im sure each time I think I have everything I need I'll be sorly mistaken.
     
  5. RocketMonkey

    RocketMonkey Active Member

    Messages:
    255
    Location:
    Kansas city area
    So I'm slowly moving forward on getting this thing ready, I figure Ill start with the missing stuff. The schematic has the drawings for the detector, matching pad and "auto radio adapter". What is the auto adapter anyway?

    For the detector should a 1N270 diode work? Also C26 shows "220" with no unit of measurement and is not in the parts list. I'm going to assume C25 is .001 uF. Also I'm guessing that the caps should be fairly high voltage rated to reduce risk of problems if they are hooked up incorrectly, or to a tube tuner. Should these be in shielded boxes? I have not yet read the whole manual so I suppose I should start on that tonight.
     
  6. Steven Tate

    Steven Tate AK Subscriber Subscriber

    Messages:
    1,846
    Location:
    Burleson, TX
    I have a New-To-Me SG165 that I have never used, but want to learn to do some alignment work. I've been told I really ought to have a THD analyzer too. Another tool for the list. Unfortunately, my work area is completely packed up for a move to another house. I'm likely to be down 2 or 3 months, so the best I can do is live vicariously through other AK members. Keep this thread going as you learn more. It will help me when I get to the point where I can try my SG165 out. This one does appear to have all of the leads and probes. I am hopeful that it is operational.
    Steve
     
  7. RocketMonkey

    RocketMonkey Active Member

    Messages:
    255
    Location:
    Kansas city area
    Id love to see the guts and construction of the probes. Too bad its all packed up. As to the thread perhaps I'll try and make the thread a learn from my mistakes and do it right the first time guide. Go through building a setup to learning to use it.
     
  8. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Messages:
    921
    Location:
    Yorktown, VA
    If you'll post photos of the schematics, that would help us answer your questions. ;)
     
  9. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Messages:
    921
    Location:
    Yorktown, VA
    I wonder how similar those probes are to the demodulator probes for other Sencore gear, for example:

    sencore demodulator probe schematic 2.jpg sencore demodulator probe schematic.jpg
     
  10. RocketMonkey

    RocketMonkey Active Member

    Messages:
    255
    Location:
    Kansas city area
    Unfortunately they are not similar.
     
  11. RocketMonkey

    RocketMonkey Active Member

    Messages:
    255
    Location:
    Kansas city area
    20170405_203131.jpg

    In the notes it states that all capacitors with no units marked are pF if more that 1 and uF if less that one. However no parts list and no voltage or type listed.
     
    dlucy likes this.
  12. RocketMonkey

    RocketMonkey Active Member

    Messages:
    255
    Location:
    Kansas city area
    Part number for detector is 39G45
     
  13. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Messages:
    921
    Location:
    Yorktown, VA
    According to the Internet, 1N774 is a "60 V, 500 mA, gold bonded germanium diode" and "forward voltage 1V" so you could guess the other components' operating parameters from that.

    My guesses, for the detector probe would be:

    R405 27K 1/4W
    R406 47K 1/4W
    R407 470K 1/4W
    R408 47K 1/4W
    C25 0.001 uF 60V - 80-C124C102F1G KEMET 100 pF 100 VDC axial
    C26 220 pF 60V - 80-C410C201J1G KEMET 200 pF 100 VDC axial
    CR401 1N774 - looks like you could use a 1N4148 or 1N914 - 512-1N4148 FAIRCHILD 100V 4A axial​

    There are a good number of "I built my own probe" pages on the 'net. I don't think you need a shielded probe, but you could use a small copper or aluminum pipe as the shell and have some amount of shielding (as well as a convenient source for the shell).
     
  14. dlucy

    dlucy dlucy67 (Doug) Subscriber

    Messages:
    921
    Location:
    Yorktown, VA
  15. ConradH

    ConradH AK Subscriber Subscriber

    Messages:
    6,843
    Location:
    Canandaigua, NY
    1N270 should work OK.
     
  16. Steven Tate

    Steven Tate AK Subscriber Subscriber

    Messages:
    1,846
    Location:
    Burleson, TX
    If you get to the point where you really need a picture of a probe, I can get to the box it's packed in pretty easily. I wouldn't mind retrieving it from the box if it would help. I'm not sure if I have every probe, I just know there are several of them in the compartment in the back, and at first glance, they appear to be in almost new condition.
     
  17. ConradH

    ConradH AK Subscriber Subscriber

    Messages:
    6,843
    Location:
    Canandaigua, NY
    I think my probes are sealed cylinders so you can't see inside them. Just follow the diagrams and it's hard to go wrong.
     
  18. RocketMonkey

    RocketMonkey Active Member

    Messages:
    255
    Location:
    Kansas city area
    20170406_201536.jpg

    I'm going to try and order caps tonight. Looks like it will suck a little bit getting to some of them.
     
  19. RocketMonkey

    RocketMonkey Active Member

    Messages:
    255
    Location:
    Kansas city area
    Im glad i took it all the way down... the capacitor for the IF rocker had 2 fins making contact. All the grease has turned into crud and some one has torqued the crap out of the knob set screws (side note, why do people feel the need to tighten small hardware so damn tight?). Other than the burned transformer this thing isn't to bad inside.
     
    dlucy likes this.
  20. RocketMonkey

    RocketMonkey Active Member

    Messages:
    255
    Location:
    Kansas city area
    C55 on the audio board was installed backwards according to the silkscreen. However looking at the circuit it was in the right way. Interestingly the schematic shows it installed backwards. 12 volts on cathode with the anode grounded.
     

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