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Realistic DX-300 preselector mechanism nightmare

Discussion in 'General Technical Questions and Answers' started by KJ6ZOL, Mar 25, 2020.

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  1. KJ6ZOL

    KJ6ZOL Ham Member QRZ Page

    I picked up a Realistic DX-300 last year at the Valley of the Moon (Sonoma, Calif.) hamfest. At the time, I plugged it in and noted that the khz part of the display lit up, but the Mhz did not. It then went into the closet for later.

    Well, due to current events I now have plenty of time, so out it came. Plugged it in and the readout read "6. ". Uh oh. Took it apart and noted that the mechanical gear system that controls the Mhz section of the system was frozen (this rig has separate tuning for Mhz and khz) and that the preselector mechanism was frozen as well.

    A little isopropyl alcohol and Deoxit got the Mhz tuning going again, but not the preselector. While fiddling with it I noted that the outer (the part that the knob hooks on to) preselector tuning shaft seemed to turn, but that the mechanism itself did not. I quickly realized that some doofus had tried to use brute force to unjam the mechanism, and thus snapped off the part of the outer shaft that the knob hooks on to! :eek::eek::confused::confused: So, I guess it's dremel time.

    I would like advice on how, first of all, to completely remove the front, as there are several elements that seem glued in place (like a knob labeled "fine tuning") or if removal is possible. Then I need to figure out how to dremel the broken part of the shaft off without wrecking anything else. Then it's back to the preselector mechanism, which is stuck fast despite enough isopropyl and Deoxit to make a nice little puddle on the bench. :eek: Any ideas?
     
  2. KF5FEI

    KF5FEI Ham Member QRZ Page

    Likely to be a service manual floating around on the intertubes. Radio Shack did publish manuals at one time, and perhaps one of the overseas sources has them online.
     
  3. KJ6ZOL

    KJ6ZOL Ham Member QRZ Page

    I do have a service manual pdf OM, but it's not very good. Looking at the exploded view of the chassis, it appears that the preselector mechanism was considered one single unit and not separate parts. The front panel can be removed only so much until one encounters glued in place parts. Typical 70s low end Japanese construction-this rig was made by GRE which eventually became Alinco, need I say more?
     
  4. N8YX

    N8YX Ham Member QRZ Page

    How much did you pay for the unit?

    Might keep an eye on eBay or the various Classifieds for a junker to use for parts. The readout driver ICs have been known to fail, and a replacement can't be sourced - so you might be able to obtain a defective unit then play swaptronics and end up with a working set.

    Should you be able to find a DX-302 on the cheap, that one's considered the better of the line. Similarly, a Yaesu FRG-7000 (which has the same overall RF design) is another option.
     
  5. KJ6ZOL

    KJ6ZOL Ham Member QRZ Page

    I paid $30, the seller said it was from an estate so he knew nothing about the rig. When I first plugged it in I seemingly could rx stations, but the Mhz portion of the display was not lit, and the khz wouldn't tune past 999. Now that I've got the Mhz mechanism unlocked, I may fire it back up and see what happens. (Hopefully not BOOM!!!! :eek::confused::p ) If the problem does turn out to be the readout IC's, then I will have to look for a replacement on ebay. Same for the preselector, it is likely that I will have to replace the whole preselector unit. As for the Yaesu Frog series receivers, I had a 8800 for a while and didn't like it, any flicker of power would send the circuitry into a tizzy and I would have to fiddle around to get the rig to work again. Although I use a FT-950 for a main rig, I'm leery about buying another Frog. I've had an Icom rig suggested to me a couple times, but they are really expensive, starting at several hundred dollars.
     
  6. N8YX

    N8YX Ham Member QRZ Page

    An FRG-7000 and an FRG-8800 are two entirely different animals. Think of an FRG-7000 as a digital-readout version of an FRG-7, which is a solid (albeit simplistic) receiver.

    The DX-300/302 also use the Barlow-Wadley HFO generation scheme which the early Frogs did, along with a tuneable preselector. The main differences were in the IF strips (i.e., filtering) and the DX series are more prone to drift and overload (in my experience) than the FRGs.

    There have been a few IC-R70s on eBay as of late in the $200-250 range. Some time ago I gave $275 for one which came with all filters and options including the FM board. An R70 is a pretty solid piece of gear, albeit with no memories (apart from dual VFOs). Nevertheless, it's a step above the Radio Shack line.
     
  7. KJ6ZOL

    KJ6ZOL Ham Member QRZ Page

    Once hamfests start back up again, and I have a little spare cash, I may look for a R70 or maybe one of the early Kenwood digital readout receivers like a R-600. (I think that's what the pre-R-1000 digital readout rig was called.) Dunno if I want to shell out that much cash for a rx this year though.
     
  8. N8YX

    N8YX Ham Member QRZ Page

    I'd go for the R-1000. An R-600 isn't even in the same ball park.
     
  9. KJ6ZOL

    KJ6ZOL Ham Member QRZ Page

    GOOD NEWS!!!! IT SINGS!!!!

    Plugged it in, turned it on, no Magic Smoke, so I fiddled with it a little and eventually the khz display popped back on. Finally read the flippin owner's manual this morning (not service, OWNER'S) and the khz reading only goes from 000 to 999. A separate control controls Mhz. If you tune the khz too far, below 000 or above 999, it will flicker off. (Like I said, 1970s low end Japanese design. The Chinese put out similarly weird radios in the early days of mass produced PRC SW portables in the early 2000s.) The Mhz linkage needs to be aligned-I'm pretty sure that there isn't a US "Jesus blaster" stn on 7120-but other than that it works ok, seems like. So I'll align it, and then into service in the shack it goes. Considering these go for $150+ on ebay, $30 is a pretty good deal.
     

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