SunnyBoy SB 2500 repair

Something different to repair this time. My neighbor’s solar inverter suddenly stopped working. He already replaced it with a newer model, but would like to keep this one as a spare. So, he asked if I could take a look.

The first thing that came to mind is: how do I power this inverter. I need to test the DC side of this – and it needs quite a high DC voltage. I solved this by wiring two transformers back-to-back with a simple bridge rectifier and a smoothing cap. So it basically serves as an isolation transformer. But with high DC voltage, you need to be really careful.

So, testing with the DC voltage – dead. Absolutely nothing. Checking the filtering caps – everything looks fine, but nothing powers on the logic board. I get power until the transformer. And yes – visual inspection reveals there’s an issue with it:

In the lower left corner, you can see there’s a brown spot. Desoldering reveals more damage – the primary winding is completely carbonized.

The transformer is a Pikatron WP1087/4g. It’s unfortunately a custom component from SMA. Neither SMA, nor Pikatron want to cooperate on specs. A shame really, for a company that sells green tech. The #RightToRepair movement hasn’t caught on there. A 20 Euro component, tops – but unavailable.

Local companies specializing in PV inverter repairs didn’t want to help out – instead quoting me investigation fees. I don’t need quotes – I already know what’s wrong; I just need the part. Luckily – I found a Dutch company willing to help. A big thanks to Interpaul BV – they supplied me a transformer at a decent price, and I gave them a little extra for their trouble. Win-Win, right?

A couple days later, the transformer arrived and I soldered it in. Works like a charm. Another good piece of kit, saved from the dump. SMA really need to step up their game to allow access to their custom components for repairs. Right-to-repair _is_ a thing, and it’s good for the environment.

73 de ON8AD

Kenwood TS-950SDX

Recently, Wim, ON4CGB, went to Friedrichshafen and picked up a nice-looking Kenwood TS-950SDX.

The seller assured him the transceiver was in perfect working order and contained all filters.

As it soon turned out, it wasn’t OK; and there were filters missing. Upon receiving signals on the main VFO, the audio sounded like the transceiver was placed under water. Apparently, a known issue with these transceivers. Normally you re-solder 4 resistor networks near the CPU and you’re done.

Alas, in this case, upon opening the unit, it was immediately clear that someone had tried to patch this up; and a trace was missing to the CPU! I removed the resistor network first, so I could clean up the area. It’s quite noticeable were the trace is missing. It’s the second trace; top right; of CP1.

I couldn’t run some standard magnet wire, as it was a bit too small to handle, and the resistor network needs a decent amount of heat to be properly soldered; so I had to make a small wire jumper. Works perfect, and the OM is happy again.

However – very bad practice from the salesman. Turns out the SSB narrow and CW narrow filter are missing. In any case, the OM at least has a working transceiver again.

73 de ON8AD

Kenwood TM-241 – No TX

One of our club members recently requested me to take a look at a Kenwood TM-241 he bought a couple of years ago, but never used it. He plans to use it just for some monitoring of a couple of frequencies for local traffic.

In any case, RX is just fine, however, when clicking the PTT-button, nothing happens. No TX.

These transceivers are known to be – let’s say – “difficult” when it comes to the PA stage. They use a monolithic module which houses the complete PA. They tend to fail.

Upon inspection, someone had already been in there, and there was cooling paste between the heatsink and the module. The PA wasn’t dead either. It just wasn’t TX’ing. I remembered that the OM said that he tested the mic on another Kenwood transceiver, and it was working fine.

Could there be an issue in the front panel? I disassembled it a bit more, and yep, there’s the issue.

Kenwood used some kind of glue to tack down SMD components before soldering (I suppose they used wave soldering, hence tacking components down). Nothing wrong with that actually, however, the glue they used, absorbs moisture with time. This in turn, turns it acidic.

The trace damage can be seen in the middle – follow the trace of the center pin of the connector down, and you’ll see it. The part of the trace that goes up was also starting to go bad.

The ground trace for the mic was completely eaten away. After recreating the traces with some enameled wire, everything was fine again. Happy days.

73 de ON8AD

Kenwood TM-V71 low power

…Or not? Here’s a short post about often overlooked issues with supplying power to your mobile rigs (or any rig for what it’s worth..); Here’s the story I told to the owner of a Kenwood TM-V71…

First of all; let’s start with some basics:

  • Ohm’s law
  • Resistivity of a wire
  • Contact resistance

We all know, that the higher the resistance, the higher the voltage across the component. Ohm’s law right? Imagine your power supply wire is a component.

Every gauge of wire has a certain resistance for a certain length. The thicker the wire, the lower the resistance. Choice of material plays a great deal in this as well.

Contact resistance. Often overlooked. A picture is worth more than words:

This is what contact resistance does. The fuse itself survives; but due to lack of good contact between it’s blades and holder – be it due to oxidation, bad design, or lack of pressure – the resistance will cause heat to be formed in the holder. Eventually degrading it further and further.

In short, the ‘repair’ of this TM-V71 was one of refreshing some basics to the user.. Lengths of thin wire, with cheap fuse holders and a plug that shouldn’t be there is a big no no.

Ham radio operators: keep power runs short, with thick wires, and premium fuse holders. Always. No exceptions.

ICOM IC-910h – Preamp bias troubles

Recently I was asked to take a look at a IC-910h VHF/UHF all-mode transceiver which had developed an issue where the bias kept being enabled. Even on transmit and when the preamp wasn’t enabled. It luckily didn’t cause any havoc as the operator’s antenna wasn’t DC shorted at the time..

If you look at one of my previous posts – you’ll know how a basic bias circuit works (check it out here – SEA remote ATU bias & mods).

The problem here, was that there was no way of turning it off and on. Nothing seemed to be burnt out or shorted on first sight. So what does this look like on the schematic?…

I’ve traced some lines to show you how things work. Q702 is a PNP transistor – a Rohm 2SB1132 T100R. This is the main switching transistor. Rated 500mA. Q703 is a DTC114EUA T106. A bit of a special beast. It’s a “digital transistor”. It has built-in bias resistors to enable the configuration of an inverter circuit without connecting external input resistors.

So to troubleshoot, I first checked if VPRI was being switched from the main processor with reference to ground. It was. Pfew – no main processor issue. Next step was to check if Q703 actually did any switching: it did as well. Hmm, odd.

Checked Q702; and it wasn’t shorted when checking in diode test from Base to Collector, or Base to Emitter. Maybe C703 or R702 failed? Nope, not that either. Any tin whiskers around due to lead-free solder? Nope.

I still suspect Q702, as for some reason, it conducts, without anything applied to the Base. (Otherwise known as a “Leaky” transistor). To confirm, I replaced it temporarily with a bog standard BC560. Works like a charm. Leaky transistor confirmed. Here’s the testing bodge in all it’s glory.

I quickly ordered a couple of Rohm 2SB1132 T100R from (I kind of like their fast service and clear website to be honest..). Delivery took a little longer than usual due to the fact that it was in stock in a HK warehouse and I’m in the EU.

Remember to really clean up the old pads when working with SMD components. It’s just much nicer. I used Chemtronics fluxed solder wick here. Pads clean up nicely with it.

Here’s the new part installed. Looking great.

And confirmation it works and can be switched on/off..

The UHF part is similar; so if you run into issues where bias is kept on with your IC-910h; make sure to take a look at these components. The UHF part is a bit trickier, as you need to disassemble the entire PA unit..

73 de ON3AD – Jeffrey

FT-2000 – Deaf as well?

I recently had a look under the hood of an FT-2000; and just as I’m done repairing two FT-897; I notice that the FT-2000 should be a suspect as well! Yaesu: what gives?!

You can see the same white oxide leaking out of the porous plactic of those filters.

A warning to FT-2000 users: you should check them periodically.

Yaesu FT-897 – Deaf on receive

In our local ham radio club ( UBA-ARA ) – two of our club members had a Yaesu FT-897 who seemed deaf in certain modes. I took both transceivers home with me and took a closer look.

Upon opening the transceivers, I quickly saw what looked like water damage on the IF crystal filters:

You can see some white deposit on those filters. My guess is that after re-flow/wave soldering these boards, Yaesu probably washes these PCB’s. However, the plastic used in these filter either is brittle, porous, or the bottom isn’t hermetically sealed.

Removing these filters is a pain in the ass. And I’m not overreacting here. The ground plane in this PCB is quite good and you can really struggle to get the solder out. (lead-free as well!). Here’s the PCB with the filters removed:

Looking at the flux in other places on this board, I suppose this transceivers has had work done before…

I opened up one of these filters to get an idea of the damage done. A sharp blade does the trick:

You can clearly see the copper oxide. No wonder this thing was deaf!

Anyway, it’s worth opening up your transceiver if you have an FT-897 to check and see if there’s any of that white “powder” on those filters. Big red flag if you see it.
Here’s a picture with already one new filter in place. Make sure to put the right filter in the right place…

Yaesu FT-450 – deaf on higher bands

I’ve always wondered why my FT-450 I bought second hand had a lower RX level on the higher bands, starting around the 20m band. I took a look at the schematic, and the input on the RX side is very classic: a DC blocking cap and protection diodes.

Protection diodes, wait – those aren’t RF protection diodes; they are bog standard SMD red LED’s! What was Yaesu thinking here? (“Let’s save 2 cents?”). Only reason they might have used these (and the only reason I can think of) – is that they maybe have a low capacitance. But seriously, Yaesu.. ?

Anyway, I set my multimeter to the diode setting and quickly realized that one of them was shorted. Really, who tries to use LED’s as protection diodes? Really not up to the task. Here’s one that was still working. The picture gives a good indication where you can find them on the PCB (underside of the transceiver).

The diodes are placed anti-parallel to clamp any over-voltage/ESD. But there are better parts to be found. I came across the Infineon ESD0P4RFL. It’s quite a bit smaller, but we can move the part a bit. It’s actually made for these purposes:

  • Very low line capacitance: 0.4 pF @ 1 GHz ( 0.2 pF per diode)
  • Very low clamping voltage
  • ESD protection of RF antenna / interfaces or ultra high speed data lines acc. to:
    • IEC61000-4-2 (ESD): ± 15 KV (air / contact)
    • IEC61000-4-4 (EPT): 40 A (5/50 ns)
    • IEC61000-4-5 (surge): 5 A (8/20 μs)
  • Ultra small leadless package:1.2 x 0.8 x 0.39 mm³

Read that last line, yes – THAT small

I cleaned up the original location of the LED’s with some solder wick; also cleaning any flux residue on the board with IPA as flux does have a capacitive effect. I removed a bit of solder mask up the trace a bit as to fit the component correctly and applied some solder paste before re-flowing the part. Measures like a standard diode with a voltage drop of about 0.6 V – so easy to verify. It’s really small compared to the original LED’s – check it out at the bottom right of the trace.

Overall if you have a FT-450 – check that these aren’t already blown. I see *some* complaints about bad RX on these transceivers, but that’s really not the case *if* these diodes aren’t blown. So check up front, and replace “just in case” would be my advice.

DIY reflow oven

So I’ve been messing around with SMD component level repair and building for some time, but for more complex boards with things other than discrete components – a regular hot air station just doesn’t cut it. Also when working with 0402 or smaller, they just get blown away.

The solution to all of this, is to get a reflow oven. The bad part? Expensive. The solution? DIY!

I did some research and there are some things you need to look out for:

  • Ideally; you want quartz heaters – as these have low thermal mass, you’re able to switch them fast
  • The smaller, the better (well, in relevance to Wattage). Mine is 9L
  • Wattage: the more, the better. My 9L oven has 800W
  • Thermal Insulation. This is where the cheap ovens suck; they lose heat fast. This can be remedied with ceramic insulation mats. My oven had a double front window, so that already helps a bit.
  • A fine grill is preferred over a baking plate

I ended up buying a small oven on Amazon, a BlackPear BFO 09. Doesn’t look too bad and actually isn’t bad at all.

How do we turn this into a reflow controller – better yet – how do you reflow boards? The first thing to know, is that in order to do reflowing, you need to get two things:

  • Name brand solder: get good solder paste; that can be traced to a real manufacturer
  • The reflow profile for that solder paste

What’s a reflow profile look like?

You’ve got 5 phases in a reflow:

  • Ramp-up: generally to bring to oven and board to a certain stable point that isn’t too far away from the actual reflow temperature. This helps cope with “lag” due to thermal mass.
  • Preheat/soak: every component picks up humidity, even your PCB and solder paste. This phase makes sure everything is gassed out. It’s the longest phase in the reflow profile.
  • Ramp to peak: the flux will get activated, components will start to align themselves
  • Reflow: once you hit liquidus temperature – the components will further align themselves due to surface tension and get soldered to the PCB.
  • Cool-down: you want to cool down fast, but not too fast. We don’t want components failing due to thermal stress.

For home reflow, get leaded paste. Seriously. No you will not die from using this (just wash hands afterwards). No you will not inhale lead fumes (gassing temperature of lead is way higher). It helps keep temperature down, makes better joints, doesn’t grow whiskers,… Get lead!

Okay – back to the oven. So yes: it’s not a matter of just cranking the heat up and cooking it like a cake.

I found a nice looking reflow controller on Tindie (yep – no point reinventing the wheel and I’m also busy with work and family..). It’s a controller created by CraftyCrow. He’s based in the UK so that means no import duty for us EU citizens.

It works with a bluetooth app on your Android Smartphone, so you can have multiple profiles depending on the solder you use. To be honest, the app still has some quirks, BUT I’ve been in contact with CraftyCrow themselves and they reply pretty fast to any questions you have. Also, they’re working on an app update.

You’ll need a couple more things to finish the build: a Solid State SSR + heatsink (I use a cheap Fotek one, might be a clone, don’t really care), a K-Type thermocouple (an exposed tip is best – you know – the ones where you see the actual weld) and some bits and bobs like a housing and power supply.

The Fotek Zero-Cross SSR

The steps to take are the following:

  • Bypass the timer (I didn’t bypass the temperature control, as I keep it as failsafe as it’s maximum temperature is higher than the reflow temperature. Think of it as thermal runaway safeguard)
  • Put the SSR in series with the quartz heating elements
  • Put the thermocouple above the reflow area, i keep it “hovering” above the pcb area, as close to the PCB itself (or even touching it)
  • Hook up everything including the powersupply

In the end, you end up with something like this. You can barely see the controller hanging on the right side of the oven, mounted on the SSR heatsink (It doesn’t even get warm, so perfectly safe).

The oven tracks the reflow curve amazingly well, considering what I’ve payed for it. For the cool-down phase, I just crack the door open a bit. And it’s fine..

I love the smell of baked PCB’s in the morning

Works great, cost me in total about 80 EUR. Highly recommend building one. Much easier for building items in comparison to a hot air station. Don’t get me wrong: the hot air station is great for rework, but not to do initial assembly.

73’s de ON3AD


Sea 1612c Remote ATU – bias & mods

So I acquired a SEA 1612C remote ATU for cheap, but without an enclosure. I figured I’d buy my own enclosure anyway, so no big deal.

As I didn’t want to use any remote cable at all, I had a little challenge:

  • I need to give it power. Okay, that can be done via a bias-tee. The tuner isn’t made for it, but can be modified.
  • I need some way to be able to “tune-on-demand”. I settled on a small Arduino Nano, but will eventually do this via a ESP8266 (I can remote control it via WiFi then)

So what is a bias tee? It’s actually no more than a handful of components: a couple capacitors, some ferrite to make a choke, and some nuts, bolts, sockets.. and a fuse. You double up these components to make one for the other side as well.

So what’s it look like? Well, see below. C1 in my case is 2x 10nF – 3kV capacitors (in parallel – so 20nF in total). F1 is a Ferroxcube 4C65 ferrite, wound with about 30 turn of magnet wire. It makes a nice 3-30MHz choke when testing it with a Vector Network Analyzer. F2 is a 3A fuse.

So how does it work? Well – RF in to the left – the capacitor blocks any DC; the choke blocks any RF going back into the DC supply. Build the same thing twice, and you can run DC over the same coax. Easy, nice, elegant. Great!

Alright, that’s one solution. Now we need to be able to “tune on demand”. There’s a pin called “DTN” on the connector block of the SEA 1612c – “Demand Tune”. The thing is:

  • This only works when it already has a stored tuning
  • Keeping this permanently low (instead of the usual “high” impulse when triggering something) locks the microcontroller up, as it’s on an interrupt pin. So no easy fixes.

Simple solution: slap on an Arduino which pulls DTN down, only once, after being powered on 3 seconds. Just an NPN and an Arduino, collector to DTN; gate to the Arduino output pin and emitter to ground.

I piggybacked the Arduino on the 5V regulator on the board (7805 regulator) so in terms of power: no issue.

To force a re-tune, I press a normal-close momentary switch which breaks power to the tuner. Upon release power is fed back to the tuner. I press PTT which recalls the previous setting. After 3 seconds, the Arduino pulls the DTN line low, causing the tuner to clear the memory setting. I can then put some RF on the tuner and it’ll force re-tune for that frequency.

I found a nice enclosure for the tuner at, a German web store. The enclosure is IP65 rated, well priced, has a window, and comes with all locks and mounting hardware.

I used two aluminium “L”-profiles to securely place the enclosure in the ground. Here’s the end result feeding my 40m long multiband half-wave end-fed antenna.