Wednesday, 18 October 2017

Metcal MX-PS5000 repair.

Been very busy, in a commercial sense, building some transmitting equipment ...

... and just as I'm about to solder the last two wires on the front panel of said equipment, the iron goes cold ...

The soldering iron in question is the very, very wonderful Metcal MX-PS5000 system. I used to think Weller made the rolls-royce of soldering irons, but these things are just in a different league!

They heat the element by RF induction heating. 13.560 MHz to be precise. It's got all manner of error detecting, it'll put itself to sleep when not in use, and also has outputs for two irons. It's also expensive.

So I think, it's probably gone to sleep ... nope.
Perhaps the tip has failed? No... (takes two seconds to change too!!)

Damn ... the emergency iron is flagged into service, and the job finished...

A new MX-PS5200 is ordered (at about £500!.. ouch). We simply can't be without it.

But let's see if we can't do anything about the old one...

Firstly, remove the retaining nuts from each of the F-connectors.

Flip the unit over, and remove the 4 security torx screws, one in each corner.

Right, that's got it out. To remove the board there are several small screws to undo, and remove the screws from the heat sinked (heat sunk?) devices, noting which are insulated from the heatsink, and which are not. The wires connecting the power supply in the back and the main board are quite short.

First thing was to check the presence of the +48V  and  +24V supplies from the switched mode mounted in the rear third of the enclosure.. all present and correct... damn.. out goes any ideas of a blown fuse and a quick-fix! There's no hope of getting a schematic, so it's down to the poke-and-hope method of fault-finding....

Checking a few parts, shows the main output FET to be dead short ... It is (or rather was) an IXFH12N50P, which is no longer available. An IXFH16N50P looks like a good candidate, and is pressed into service.... still not warming the iron... damn. It's gate is driven by a drive amplifier, which is in turn driven by an oscillator formed by a crystal, and a 74HC04 hex inverter... the hex inverter is duff, and is replaced, and so is the supply to the drive amplifier...

It's an LM2576-ADJ (not that you'd know from the photo) .... and replacing that restores the supply to the second stage of the drive amp, but not all of it .... damn.

The final piece of the jigsaw is D12 in the small switched mode buck converter .... it too was dead short ... lord knows what the original is, there's no circuit anywhere on the web, so I selected a 1N5819HW for the job, based on the datasheet for U3. It's physically smaller than the diode it replaced, but it seems to work! I've got a hot iron!

Excellent ! We now have a spare in the workshop.

Not sure I like Metcal's new logo much ...

Saturday, 30 September 2017

BSR UA14 Monarch Plinth.

Remember my BSR UA14 record player from a while back? (No? Click here!)

Well, it deserved more than an Asda cardboard box to sit in. 

My friend Julian supplied a bit of plywood to make a suitable top from, and another friend, Barry, cut the required shape out (copied from another record player fitted with the same deck, and soon to be featured on these very pages). Barry also made some MDF sides for it.

Now, I could paint it ... but I've got another couple of turntable plinths made by Carl Ellis I'd like to veneer, so this would make the ideal test piece.

Some mahogany veneer was procured from the very wonderful people at who were most helpful and rookie tolerant (even sent me some free samples)

I tried some different samples out on a small wooden box, and after some initial success, got on with the job in hand...


Trimming of the edges terrified me. What if it split? I'd have to remove it and start again! I'd read on the internet that a veneer saw was the way to go, and it needed to be razor sharp. I didn't want to go to the expense. I initially just cut the veneer to the rough size before gluing with a pair of sharp kitchen scissors! I trimmed the first part with a sharp scalpel. It went well enough ... get to within a couple of mm of the edge and sand it back with some 120 sandpaper to the  edge. Don't rush any of the process. The scalpel cuts with the grain with ease. Cutting across the grain isn't so easy, and requires multiple gentle strokes. 

With a couple of off-cuts, I experimented with finishes...

Whilst varnish looks good on the photo, The oil has a better sheen to it after a couple of coats. I used Liberon Finishing oil. It seems well thought of

So, now for the big piece that will cover the top.... this was difficult to get to lie flat, and, in hindsight I wish I'd done it first. Clamping it down proved problematic!! That's two dirty great power supplies, and a wooden box full of sealed-lead acid batteries holding it down whilst the glue sets!

After everything is trimmed up, and given a brief run down with some fine sandpaper, the first coat of finishing oil is applied, and left for 24 hours...

It's then given another rub down with fine wire wool, and another coat added....

This is repeated until I've built up 5 coats of finishing oil. It's important to follow the instructions on the bottle to the letter.

Once this is finished, the wood is lightly polished up with a fluffy cloth... and I must say I'm chuffed with the results!

Monday, 28 August 2017

Sinclair Stereo Sixty Amplifier.

Colin popped by, with an unusual amplifier under his arm.

Chap's bought this off me, can you take a look?

Yeah, why not...

It's a Sinclair (Sir Clive... think of the ZX 80, 81 and Spectrum computers, and the C5 electric tricycle, yeah, that bloke) "Stereo Sixty" Amplifier.

Now back in the 60's and 70's, before Sir Clive hit the big time with home computers, Sinclair sold electronic kits, and the Stereo Sixty was the preamplifier part of "Project Sixty", which consisted of a Stereo Sixty Power pre-amp, a Z8 power supply and a Z30 or Z50 Stereo amplifier module.

There was also a "Filter module"... and a quick web search show's it looks nothing like the module fitted to this module, but does show a similar one in "Project 80", although not available as a separate unit....

Lid off, and it's definitely home-built.... Coax used to get the audio from the din plugs, what looks like coax screening stripped off and used to screen the mains cable to and from the switch (?!) ...

and some rather too short wiring between some badly fitting phono sockets, to an attenuator hovering above the board ....

Gently powering the thing up produces some audio, and quite a bit of hum ...

That big red capacitor is open circuit...

Note the "Nomark" pass transistor, and the bridge rectifier shaped like a nut!

Dated Nov '71 ... it's almost as old as me, no wonder it's knackered....

There's a few other caps that are a touch low... these are replaced.

There are two output capacitors, each 1000uF, 63v, which read perfectly.... Sadly they can't be trusted. If they fail short, it's good-bye output stage, so they're replaced...

The dodgy mains-switch wiring is replaced... Someone was obviously paranoid about hum pick up... screened indeed!

The pre-amp is removed, and checked through.

The pots are horribly noisy, but clean up well. The co-ax is removed, along with the wiring that's too short ....

... and that floating attenuator replaced with something much nicer...

and lashed up for testing ....

All cleaned up and back together. I quite like it's blue and grey case ....

So... how's it sound?

I expected to be typing "of it's time" , but I think it deserves better than that , I was pleasantly surprised  ... It's quiet, and I enjoyed a couple of Matt Berry albums in the workshop whilst it was soak testing.

Of course, being a home built kit, this would vary dramatically on how it was put together in the first place. Whoever built this example was obviously paranoid about hum pickup. It's got a reasonable star-earthed design.

The bass control's centre frequency is far too high for my liking, and the PU input (for turntable pick up) seems very "flat", I suspect it was designed for a ceramic cartridge. Other than that, a talking point for Sinclair collectors everywhere, and very usable.

Thursday, 24 August 2017

Oddball prototype Linn LP12 power supply. The Linn Wakonda.

I'm just posting this because I'll probably never see another. Apparently there are only a slack handful in existence ...

It's a prototype Linn LP12 power supply. Apparently called a Wakonda, it's a bit like a bastard son of a lingo and an axis (of evil), with a hole in it!

It's a pukka job. Obviously some sort of prototype...

It's obviously had some use as the board has discoloured from heat underneath the droppers, and, as usual, a re-cap restored operation ..... except 45 RPM....

... which was traced to two missing pull down resistors, not catered for on the board, and never fitted... perhaps the previous owner didn't have any 45's ??!

One interesting feature is the output transistors are bonded to the heatsink with some sort of cement. The digital phase generator is almost identical to a lingo, and allows LP12 users to switch between speeds without all that tedious mucking about with the belt.

Here's some photo's of it's final resting place

Tuesday, 25 July 2017

Committed to Git.

Been meaning to do this for a while...

I think they're all there.....

Let me know if they're not!

Grief with I2C library on arduino LiquidCrystal_I2C library (No display or displaying 1 character)

Oh man. I hate it when things break.

I've used a couple of these displays recently, whilst developing my next project (watch this space ... it may be Mini related!)

These are a bog-standard 1602 with a Hitachi HD44780 driver or equivalent, and mounted with a PCF8574 Remote 8-Bit I/O Expander for I2C-Bus, thus enabling a 2 wire (+ power and ground) solution. Great. 

Now when I made the GPS master clock, I used one coupled up with a 20x4 display. All was well after I tested a few libraries, I finally found one that worked.

Now something broke in the IDE. I'm not sure when, but now the library I used no longer works :(
Be very careful here, as there appear to be more than one library named LiquidCrystal_I2C ... which makes matters VERY confusing in the IDE's library manager. 

The library originally came from ...

Now if it doesn't work , open up the LiquidCrystal_I2C.cpp file in the Libraries/LiquidCrystal_I2C folder in your Arduino's default folder...

Scroll down until you see this bit:

/*********** mid level commands, for sending data/cmds */

inline void LiquidCrystal_I2C::command(uint8_t value) {
send(value, 0);

inline size_t LiquidCrystal_I2C::write(uint8_t value) {
send(value, Rs);
return 0;

Now... change return 0; to return 1; 

Like this :

/*********** mid level commands, for sending data/cmds */

inline void LiquidCrystal_I2C::command(uint8_t value) {
send(value, 0);

inline size_t LiquidCrystal_I2C::write(uint8_t value) {
send(value, Rs);
return 1;

Save the file, and try again....


Took bloody hours to find that!!!

Tuesday, 18 July 2017

Classic Mini LED indicator (turn signal) lamp replacement.

Still working on the Mini. It's coming along nicely, albeit slowly...

I did have a plan to reassemble things in a nice orderly manner. That's long gone out of the window! The best plan seems to be this:

1) Remove a part from the box.
2) Identify part
3) See if we can if the part, and if so
4) Clean/ paint the part and fit it.

With this in mind, it's recently come down to electrics.

Now the front indicator (turn signals if you're across the pond) / side lamps housings were made by lucas 39 years ago, from a sort of Mazak "monkey metal". Now this alloy doesn't age well, and mine were starting to crack up. Sadly there are long since obsolete, and good original ones now command a high price. Lenses are still available, however.

There are a couple of reproductions available. Some are quite expensive. Most seem to be made from ABS plastic of some description. Ideal. I chose these from Spyda designs, simply on price! (£31ea at the time of writing). Link Here . (Image stolen without permission from Spyda designs, sorry)

They rapidly turned up, nicely packaged.

They are quite a lightweight flexible construction, but this is no problem in use. They fit really well.

Nicely constructed, the PCB features three 1W yellow LEDs for the indicator section, and one 1W warm white, wide angle LED for the sidelight. The observant amongst you will notice there's a TO220 device in the top right hand corner, I suspect it's an LM317 or similar configured as a constant current source for the LEDs. Far better than a dropper resistor, and should ensure our LEDs have a good, long life. Great stuff!

The problem with fitting LED lamps is the dear old Lucas flasher unit buried under the dash. It's a thermal bi-metallic strip kind of thing, and relies on the current drawn by the lamps to operate. A normal flasher bulb is 21W ... these indicators are 3W .... the Lucas flasher unit just doesn't flash... it just stays lit up. This problem is exacerbated by the fact I've installed LED lamps in the rear too...

Because Mini didn't really change much with the times, there's another flasher unit by the windscreen wiper motor too! It's job is purely for the hazard warning lights (Four-ways if you're in the states!) This doesn't work either.

Now we could just shove in some 21W 6.8 Ohm resistors in the circuit in parallel with every indicator lamp (we would probably get away with 10W, as the duty cycle is about 50%), but that's a horrible bodge really.

OK, I thought about a simple 555 timer or discrete astable multivibrator driving a relay, until I looked on eBay. LED compatible flasher relays are no money ....
OK. So I ordered a couple to replace my two relays.... one turned up. Typical. (I've contacted the seller, the other is on it's way!!)

Now our dear old Lucas unit has two pins (actually some have three, but only two are connected), and doesn't give one iota about which way it's connected. This new unit has three pins, and I suspect it transistorised somewhere along the line, and is therefore going to get upset if we wire it up backwards.

The three connections are as follows....
L - Lamp - goes to the indicator lamps.
E - Earth - goes to chassis ground.
B - Battery - goes to the battery.

Only, of course it's not quite that straight forward. If we wired it up like that, our indicators would be permanently flashing, day in, day out....

So .... a quick consultation with the Haynes manual, and a poke round with the multimeter are required....

I will point out at this juncture that Mini had a long production run, from 1959 to 2000. Along the way some improvements were made to the electrics (and some of it wasn't!!). You may have a positive earth car if it's from the 50's or 60's ... you may or may not have hazard warning lights... and of course, Mini was exported all over the world, so local requirements would have changed the wiring...

Anyway... the original Lucas flasher was located hiding under the dash rail....

It's that round tin thing .....

... duly removed...

One side connects to a light green/ red wire. This is in accordance with the Haynes manual... good.

The other wire is blue with a red stripe. It *should* be a solid dark green. I can see further up the loom, that a repair has been made, and it does indeed join onto a green wire....

Now this is where things get a bit confusing. Having thought about this, I (mistakenly) thought this wire would simply supply 12V, via the indicator switch to the relevant lamp. Nope, there's a permanent 12 Volts there.... damn. This is why I have a hated for car electrics diagrams. None of the switches show a position. Scroll back up to the photo of the diagram, and have a look. 26 is the indicator direction switch. 25 is the flasher unit. 153 is the hazard warning light switch. 31 & 31 are the indicator lamps. There's obviously something missing. Some lucas magic going on in the hazard switch? There's no such thing as magic....

No, here's what happens. 12 volts gets to the original flasher unit. It's output goes to the lamps, via the indicator direction switch. Once the switch is made, current is drawn through the lucas flasher, which starts to warm a bi-metallic strip inside the unit. Once it's been on for a second or two, the bi-metallic strip opens the circuit, and starts to cool as no current is being drawn. Once it's cool, it closes the circuit again, and the process repeats.

Right, but what happens to my new flasher unit, if it's getting a supply (and earth) simultaneously? Is it going to sit there clicking away, annoying the hell out of me, even when my indicators aren't on?

As it turns out, no. It actually needs to see a load to operate, exactly like the old lucas unit. Just not much of a load!

So, the dark green wire goes to B, and a new earth wire goes to the chassis and pin E.

Works a treat....

The hazard warning flasher is wired up the same, and works flawlessly too..

Light green and brown goes to L, and the wire from the inline fuse holder, connects to B.

How, back to work.... ;)