Teardown: "HOTAIR GUN Desoldering Soldering REWORK SMD STATION 3 Nozzles RHOS Yihua 858D OZ"

Normally I wouldn't bother with a "teardown" post. They're popular, yeah, but I don't really see the point myself; it's like watching someone else eat ice-cream. But since I pointed out the potential & actual dangers of 'eBay special' hot air rework tools in my earlier post, I figured it'd be worth going through mine to uncover all the faults & explain them in a little more depth.

Opening it up, at first glance it doesn't look too bad:

Exploded view. (Note: comments and captions may not be literal…)

Crap that is useful: making it less crap

Following on from my previous post, sometimes there are fair reasons to buy crap. Which is fine, as long as you're aware that it's crap. Even then, though, it can be crap in surprising ways…

After hand-soldering tiny 3.2 x 2.5mm crystals in a couple of recent projects (& having to desolder & rework TSSOP-sized opamps to fix a pinout error … grrr, my own fault), I decided I needed a hot air rework tool. Since I'm not planning on using it a lot - I happen to like hand-soldering tiny components under a microscope* - I wasn't particularly interested in spending too much.

Enter the world of cheap and nasty hot air rework stations available on eBay. 57.50 Falling Pacific Pesos later, and I was waiting on AusPost to make me the proud new owner of a "HOTAIR GUN Desoldering Soldering REWORK SMD STATION 3 Nozzles RHOS Yihua 858D OZ".

(Alignment tool, random stuff, Fluke 19, and microwave analyser not included.
May cause death or injury in susceptible individuals or groups.)

Now, before anyone runs out and buys one on my say so (as if!), go read the thread on EEVblog titled "DEADLY WIRING FAULT ; Atten 858D+ Hot Air Rework Station". It's not just about the Atten branded ones; it's applicable to all of the cheap stations like Aoyue, Youyue, Saike, Xpower, WEP, Yihua, etc, etc. And not just minor issues - problems found include mains active wired to the metal barrel of the handpiece…

(Note: if you're looking for a teardown post, this isn't it - but I might do one later. Feel free to read on regardless!)

Crap that is crap

Cheap stuff is crap. Everybody knows this, including me, and we just deal with it. Here's one way that bit me last week…

The other day I needed a new heel for my shoe, so I decided to go to Morganville (which is what they called Shelbyville in those days) stereo 3.5mm cable for a couple of projects (a USB audio interface & a simple SDR; details in a later post), so I went down to the local sex-toy shop …

 Then ... and now ;)

… and bought a couple of cheap 3.5mm stereo plugs to upgrade my old home-made 3.5mm mono-to-stereo cable. Did the usual "be vewy, vewy quiet careful" dance when soldering them - gripped firmly (but not too tight!) in the soft jaws of the mini-vice (by the collar, not the shaft [as it were…]), plenty of flux, dialled in an appropriate iron temperature, used pliers to heatsink the terminals while tinning & soldering (so the plastic doesn't melt), etc, etc.

Result?

Why I Still Hate The Arduino IDE; or "How Come The NMU-7700 Software Isn't Ready Yet?"

I've been adding stuff to the NMU-7700 page over the last week or two - I wanted to quickly wrap it up for now so it's done, ready to build, & I could move onto other things. So far all the hardware stuff's there; what's missing is the firmware/software.

Which is where the post title comes in…

Sad news, but some good news

First, the sad news:

Ron, a.k.a. "Thinking Brain Dog", passed away a few months ago. Not only was he my friend, but he was the fingers - and at least half the brain - behind this blog.

And now, for my next trick...

With the heavy lifting of the memory unit out of the way, I'm thinking of other things. First cab off the rank is an improved IF buffer amp…

A few months ago I posted a quick write-up of a design I did many years ago, not too long after DRM first started appearing on the airwaves. It was a pretty straightforward JFET + 2 BJT design, nothing special - but it did the job. I've never been entirely happy with it though and, since that amp has graced a friend's set for years, I figured I'd build something better for mine ;)

An Updated Memory Module : Part 4 - It's Alive!

It's taken a while longer than I had planned, but it's finally done:

A fully-functioning, DIY, self contained, built from scratch memory unit for the FRG-7700!

I'm calling it the NMU-7700.

Still alive!

Just a quick post to remind people I'm still alive, and to let everyone know memory unit development is picking back up again after a short medium hiatus due to work, parts delays, and general Life.

The new & slightly redesigned main boards (smaller! better! same speed!) arrived a few weeks ago, one has been assembled for testing, all the individual functions have been proven, a few component values have been tweaked (to ensure signal levels etc. are spot on), software is being re-written to handle the design changes (and make ongoing development easier), and I'm walking backwards for Christmas...

Slow goings

I haven't had much chance to work on the memory unit software recently - lazy, then a dose of the 'flu, followed by extremely busy - but it's progressing along, albeit slowly. Soon, I promise, soon…

In the meantime though I've had emails from a few people who've been following along. Some have pointed out errors (thanks, I'd already caught most of them!), most have wondered if I'll be selling completed units or kits (more on that later), but one gave me a bit of pause. After nicely pointing out a few mistakes I've made, they wanted to know if I could help with faultfinding their factory-fitted memory unit by checking some signals & making a couple of measurements on my MU-7700.

An Updated Memory Module : Part 3a - Main Board Build

We have boards!

02/08/14, AM: Main boards arrived yesterday!

A little slower than usual (just under 3 weeks, vs just over 2 weeks in the past), but I'm not going to complain. I'll reserve my complaining for the idiot who ordered the wrong voltage regulators (TO-263 vs DPAK/TO-252); he has been given the task of finding the correct regulators on a Saturday morning. Not easy in a world where the main electronics hobby chain stocks more farting toys than surface-mount components…

For a change, I think I'll keep updating this post as I build and test the board - you don't want to dig through multiple posts, and I don't want to make them.

More when I get back from my search…

An Updated Memory Module : Part 2a - Hardware Changes, Demo Software

I know, I know … last time I said I'd post some very basic software soon. And, slackly, I haven't. Here's why…

The short version: after the first home-made prototype of the interface board I made a few changes to the circuit, re-designed the board, sent it out to have a small run professionally made, started work on schematic for the main board, ordered the parts for both, and planned to release a quick demo package after building a new interface board (rather than release my mess of spaghetti code and half-arsed functions as a 'demo' that'd need modification to work with the new design).

Most of that went swimmingly. But…

An Updated Memory Module : Part 2 - A Bare-Bones Prototype

Since I said in Part 1 that knowing most of the the detail of how the memory module works was unnecessary, and reckoned you could just about build a memory module knowing nothing more than the basic inputs and outputs, I suppose I'd better put my money where my mouth is.

Well, here we go…

An Updated Memory Module : Part 1 - How the hell does it work?

Have you ever looked at the memory module circuit?

I mean, really looked at it?

It's actually pretty trick, and a nice example of how analogue & digital electronics were being married in the 70's. It's also deceptively simple in what it does, and only slightly more complicated in how it does it.

And I'm designing a new one from scratch…

IF Output for the FRG-7700

I'm in the middle of building a new workbench for myself - well, the actual reason is to build my partner a study desk, but she's let me attach my workbench to it - so actually doing stuff has been a bit slow.

Alignment...

As I mentioned in my last post, my FRG is in need of alignment - tuning at the bottom of each band is cramped and non-linear, it falls about 50kHz short at the top end of each band (when it should go about 50kHz past the end), and the whole thing feels a bit insensitive (which may just be psychological on my part).

That's not unusual; as far as I know, the set has never been aligned since it left the factory 30-odd years ago, and being kept for a few years in a hot shed won't have done it any favours.  At least it hasn't been "adjusted" by someone who's skills would be more in demand in the meat production industry than in an electronics workshop. Alignment isn't hard, and is quite well documented in both the instruction and service manuals, but it does require a few tools and a certain touch…

The (slightly grainy) taste of success

(As I mentioned earlier, this and previous posts are re-worked versions of posts originally made late last year.)

Straight after I finished building, testing, & installing the new PSU, I hooked the laptop up to the FRG-7700 and decoded the following images:

Curing the power supply blues…

Original FRG-7700 power supply board.

Like most (but not all!) things, there's a lot of info about Yaesu SWL/ham gear on the internet. For starters, there's the Fox Tango International Yaesu Users Group (ye olde 80's style design!) including Wim Penders' Yaesu FRG-7700 Survival Guide, and the FRG-7700 specific Yahoo FRG-7700 users group. I'm sure you can find more…

I fully expected to find an improved power supply design somewhere, and was little surprised when I didn't. Not that it's an especially difficult thing to design, but simply because these sets are still quite popular (check out the ridiculous prices on eBay!), are now getting on into respectable middle-age, and many would be owned by people unfamiliar with electronics. The only example I could find is Wim's design in his Survival Guide - and it's deliberately more of an update/copy of the original design, with the 13.5V rail still unregulated but a LM317 regulator IC replacing the zener/Q02/Q03 discrete regulator of the original. I'm not sure why there's no other designs for improved supplies - maybe it's as simple as most sets are in the USA with 110/120VAC mains or, like Wim, are in Europe with 220V mains? Perhaps the transformer's primary voltage select taps are better suited to those voltages rather than Australia's 240VAC, resulting in the 13.5V rail being somewhere near what it should be?

Awakening the sleeping monster

Top view, showing the main board.

Here's the thing with old electronics: don't just turn it on and see if it works! Components degrade due to heat &/or moisture, vermin get in and eat important bits, corrosion destroys wiring & pc board tracks, etc.

And that goes double if it's been sitting in a hot shed with 40+°C temperatures in subtropical Queensland.

So the first thing to do was take the lid off my receiver and have a look…

Something old is (re)new(ed) again

So... I decided to go searching in the shed and dig out my old shortwave receiver.

Up, running, & tuned into a local MW NDB

I bought my Yaesu FRG-7700 second hand back in ... what was it, 1996? ... when I was still an electronics technician. At that stage I'd been a hobbyist for many years, with a passing interest in shortwave listening for all that time. When I was a kid I had a Tandy (aka Radio Shack) Science Fair "Three Transistor Short Wave Radio" kit^* which, despite being a finicky regen design with no proper tuning scale (and so to my young mind not a real radio) had fascinated me with its strange languages and odd non-voice signals. Later, as a teenager, I owned an old ex-Army "Reception Set R210" - which, with its calibrated(-ish) dial and SSB reception, was finally a proper radio^**. That set, coupled with a simple FSK decoder kit^†, introduced me to the world of RTTY and WeFax.