Diagnose and Repair a Yaesu FT-7800 Ham Radio

Yaesu FT-7800 Ham Radio

[Alan Wolke] aka [w2aew] was challenged to repair a friends Yaesu FT-7800 ham radio. This radio operates on two ham bands, 2 m VHF and 70 cm UHF. The complaint was that the 2 m side was not working but the 70 cm was transmitting fine. Alan started by verifying the complaint using a Bird watt meter with a 50 watt slug and terminating the signal into a 50 W dummy load. [Allen’s] bird meter is the type that has an RF sampler that can be connected to an oscilloscope for added signal viewing and validation.

After verifying that the radio was not working as described, Alan starts by glancing over the circuit board to look for any obvious damage. He then walks us through a block diagram as well as a circuit diagram of the FT-7800 radio before stepping us through the troubleshooting and diagnostics of radio repair. Even when he realizes he might have found the problem he still steps us through the remainder of his diagnostics. The skills and knowledge that Alan shares is extremely valuable to anybody looking to repair radios.

Spoiler alert. At the end of the first video he determines that the pin diodes near the final VHF output were bad. In the second video he reveals that he could no longer source these bad components. Through some clever evaluation of a more current Yaesu radio, [Allen] was able to find suitable replacement components. Lesson two ends with some surface mount solder rework tips as well as testing that the repair was successful.

And just in case you don’t know what a pin diode is, or is used for, Alan shares a third video covering just what this component is and does in a radio. You can follow the jump to watch all three videos.

Comments

  1. nbtmm says:

    Really? I follow Alan on youtube and i like his electronics vids but this is not a hack.

  2. Andrew Hull says:

    Hmmm.. he doesn’t perform the repair with duck tape an arduino and hot glue, but that doesn’t exclude it from being of interest to the HAD audience

  3. truthspew says:

    Yeah, I already subscribe to his vids on YouTube. I have a Yaesu VX-7r and those suffer PIN diode failures too. So his vids were extremely valuable because I know someday I’ll have to repair mine too.

    73 de kd1s

  4. Alan says:

    Well, even though this isn’t a hack per se (except for the substitution of the PIN diode part numbers), hopefully it does present some troubleshooting and rework techniques that all hakers/makers can benefit from.

  5. Clark says:

    So many people here are quick to cry “not a hack!” This is unfortunate, and rather misguided. The term “hacker” (according to some lore) originates from noise made by rapid keyboard typing shown by those with considerable skill. The skill shown in this video, like everything, is less than some and more than others. Considering the number of “[turn on and off a device] with an Arduino” and articles accepted as hacks, this one repairing radios should by far be considered a hack, and a mighty good one at that.

    Alan, your explanation of using PIN diodes as RF switches was most interesting. Thank you.

    • sbrk says:

      Yeah, HAD might as well rename itself to “Arduino-a-day”.

      Tech plus since ’93, Advanced a year or so later. Back when it still took effort to get your license. None of this “no Ham left behind” no-code for me. :-)

  6. DainBramage1991 says:

    I’d like to see more articles like this. Hacking and ham radio go hand-in-hand.

    Also, anyone who thinks this isn’t a hack, by all means feel free to spend the hundreds of dollars needed to get your radios professionally repaired.

    • J.C. Wren says:

      While I agree with you about spending hundreds of dollars on repairs, it’s still not a hack. A “hack” is fundamentally repurposing something for which it wasn’t originally intended. This is a repair. That does not mean it is without value, as many people, hackers or otherwise, don’t fully understand proper troubleshooting and repair techniques.

      Does the post have value? Without question. Is it useful? To many, yes. Is it a hack? No.

  7. Reg says:

    The significant issue is understanding how things work. Repair with or without access to exact replacement parts is the ultimate expression of this.

    I’m far more proud of repair work like driving home in a VW on three cylinders after melting a hole in #3 (I pulled the pushrods out) or tracking down the bad solder joint in a 60 MHz analog scope horizontal circuit than I am the myriad of things I’ve cobbled together from the bits and pieces I had lying around. The ultimate being the TR7 engine taken apart by someone else I reassembled from a pile of parts with no manual. All I knew was it was an internal combustion engine. Before that I “worked” on cars. After that I was a “mechanic”.

    There are plenty of people who can “hack” things they can’t repair, but anyone who can repair something can do anything they want with the pieces.

    “Spending hundreds of dollars on repairs” is just consumer mentality.

    Oh, and please explain how a build from new parts is a “hack”.

    • Whatnot says:

      pedantic – adjective – of or like a pedant.

      pedant – a person who is excessively concerned with minor detail or with displaying technical knowledge.

      That’s the best I can do, hope it helps :)

  8. Whatnot says:

    Slightly unfair since he had a schematic and a layout and a block diagram. And all those handy ground points right next to the probe points.
    But still not bad to watch though.
    It’s just that so often it’s impossible to get any info on commercial devices.

    • Mystick says:

      Companies that make ham stuff are pretty good about getting schematics out there. There’s a lot of experimentation and customization in the community – and they know it. I’ve even seen some radios where a logic map for the microcontrollers is provided.

  9. rotceh_dnih says:

    Regardless im glad this was posted. in cases like this i really dont care if its a “hack” it has it place.

  10. Ren says:

    I -KNOW- what a PIN diode is…
    It is a diode with a very sharp point at one end, sort of like a NEEDLE diode.

  11. geeky nerd says:

    I think the dual band is not attached to the motherboard so, if you intend to release the fotons of the card you MUST seal the Hijack shield and create an IFGJP shard into it in order to validate the code

  12. Mystick says:

    The finals are the first thing you should check, as they are generally the first thing to give up the magic smoke when a radio without SWR protection circuitry is connected to a mismatched load(or not connected to a load at all) and transmits with power.

  13. Switching diodes is a major failing point in radios. Pretty easy to troubleshoot. Just notice what the radio isn’t doing and check the diodes that control it.

  14. Rob says:

    Fantastic post!!! Thanks HAD! This guy’s amazingly educational… wish I’d had him as a college prof… would have been so much more informative!

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 91,402 other followers