Mitsubishi HS-M60V repair.

The venerable workshop VHS machine has finally given up after many years of sterling service. It doesn't make it into play or record. It'll be the loading belt, a small, rubber drive belt that's used to move the components of the mechanism into it's various modes. Why do I want to repair it? Because:
1) I can.
2) It's better repaired than in landfill. I hate to see stuff thrown out.
3) Because this machine is very good at recording and playing back system A video.

Thankfully a new belt kit is obtained from the lovely people at www.notobsolete.co.uk

As per usual, unplug the machine from the mains. Don't argue, do it.

There are two screws on the left and right sides of the top cover. Undo them and remove the top.

Grasp the joggly shuttler thing, and pull it off.

There.... put it safely to one side.
Undo the plastic catches holding the front panel on. Three on the top, two on the sides....








... and three across the bottom....
With a bit of jiggling, the front panel will now come off.

Put the machine on it's side.

Remove the three screws,. indicated with arrows stamped into the base plate, I've circled them in the photo.  Put the machine back on it's feet.

We now need to remove the deck. It's held in with 5 screws...

Two down the holes conveniently positioned on the cassette housing (the bit that loads the cassette onto the deck)

One to the rear right hand side of the deck...









One on the rear left...

... and one in the middle by the head amplifier.

While you're there, unplug the cable to the top of the head amplifier....

 ... and the one to the right of the cassette housing, which connects the end sensor..










You should now be able to remove the deck from the main board and case etc ... Just grab it by the cassette housing and gently pull...

Flip the deck over....

The big belt from the capstan motor to the reel drive gear is easy to get at, so replace it now, whilst we've got the machine apart.

The loading belt is located as shown by the arrow in the picture to the right. The shaft that the belt drives (the bit with the little fan on) is only held in position by the force of the belt and a small black plastic clip. Now we could disassemble the entire loading gear and gain easy access to the motor, belt and shaft, but then be faced with a re-alignment job... nah. Careful use of some small, needle nose pliers, and the belt can be worked out from around the shaft!

... and there's some access to the loading motor spindle from the top of the deck too...

The old loading belt had lost it's tension, and wasn't exactly round anymore....

Fit the new belt, Reassemble the machine, making sure to reconnect the end sensor cable, and supply to the head amp. When refitting the deck, check the large multipin connectors under the head amp have located and seated correctly. Test for correct operation. Have a cup of tea safe in the knowledge of a job well done, and another piece of kit saved from landfill! 

Meade EXT105 Telescope repair.

A while ago a friend contacted me with regards to a Meade telescope that belonged to a colleague of his. Time elapsed, and eventually it made it's way into the workshop.

This is some bit of kit. Now I'm no star-gazer (although I've always fancied the idea) but this thing looks fantastic. Once calibrated, you can search it's database and set it to automatically point in the right direction of the celestial body you wish to view. Brilliant..... except for this one, which threw a fit when asked to point to something, and smoke bilged out from the motor that makes it move up and down (I would say it's an EL or elevation motor, but apparently when dealing with telescopes, it's a DEC or declination motor, lord knows why).

Beast of a thing. First challenge was to get the optics out and placed to one side, out of harm's way... Two cap screws this side, and two the other hold the complete optics onto the base. It takes some gentle persuasion to extract them. 

There's some sort of electronics attached to the top of the optics ( not really sure of their purpose! Let me know! ) . This board and it's cover are held in place by a single cap screw. There's a 4 pin connector to undo to release it.

Once the optics are out we can disassemble the stand. Removing the cover off the motor for the DEC drive, reveals some damage!

Ugh... 

Unidentifiable burned-out IC's ...

We must never forget that electronics is driven by high-pressure smoke. You can see here where the failure has been caused by the smoke escaping from the IC's.

Emailing Meade and a few of their dealers gets me nowhere. Not even a reply. Thanks guys.

It does, however dawn on me, that the circuit that drives the Azimuth motor may be the same...

..and on closer inspection, it is certainly similar. The components are in a different position, but the circuit appears the same. 

By a process of elimination, the bits we need are a SI4947ADY & SI4936CDY. eBay is our friend. 

Each of these IC's house two MOSFETs. The SI4947ADY is P-channel and the SI4936CDY N-channel.

Having identified the parts, we give ourselves another problem! Which is which....

Having a careful look at the remains under a lupe, one IC gives us a clue, the SI4936CDY is on the left, the SI4947ADY in the middle (It's a 7805 voltage regulator on the right)

The old components are removed, and the board cleaned up. There's some damage to the print under the SI4947ADY in the middle. I have to add a tiny piece of wire here to make up the pad, and attempt to fit the IC on the top....





New IC's are fitted. I check for shorts & open circuit connections. It all checks out OK. The tiny wire under pin 1 is good to go!

 I decide to add a 0.01uF capacitor across the motor terminals to try and protect the electronics a little more from the spikes coming from the motor. I wouldn't mind betting this is what damaged the electronics in the first place.




... and then the daunting task of re-assembly. Nothing really to note here, other than be careful to route the wiring through the DEC motor board which connects to "the mystery electronics" on the top of the optics!

And then , bullet firmly between teeth.... Power-up!

  

WEM Watkins Copicat, repairs, renovations and electrical safety upgrades!

Minding my own business, when the telephone goes, and it's a friend with a wobbly Watkins that no longer works.

Cabinet's OK. Shabby chic. Hinges need replacing...

Obviously heavily gigged in smokey pubs! Tape path is dirty, and the heads are worn, but they'll go for a while yet.








Most of the caps in the supply are in poor condition. These two were replced, the originals being high ESR and low capacity. There were also two caps decoupling the +/- 12 volts rails. One was short circuit.

One of the main problems with the copicat, is it's lack-luster electrical safety. It was made back-in-the-day when standards were different. There's a nice metal box, the chassis of which is used to ground the audio incoming and outgoing. Now here's the issue. It's not grounded to a safety electrical earth. There's only a 2 core mains lead fitted. Now in this day and age , this isn't good enough. Not unless special precautions are taken (double insulated). This certainly isn't double insulated, and, although a remote possibility, if a live wire were to come off the motor or mains transformer, and connect with the metal chassis, the ground of your guitar would now be live. It's going to hurt, or kill. Not good. It HAS happened.

So, what can we do about it? Easy... fit a three core lead, and ground the chassis. Brilliant. Guitarist now safe. Except for the thing now hums like billy-o, because we now have an earth loop. More here.

OK, so what can we do? Remember the isolation transformer we fitted to the Ekco radio? Just the job. This will prevent any earth currents flowing , and prevent the thing humming whilst maintaining electrical safety. 

Here, I've fitted the isolation transformer , and a nice new 3-core mains lead. The Earth is secured to the chassis, using a soldered ring terminal, and a nut, bolt and star washer to ensure good contact

The tape-tensioning mechanism is stripped, cleaned and lubricated.

All cleaned up and ready for the next 30 years of service!

Ekco U319 Radio Restoration.

I have one of these radios myself, and it sits in my hallway, minding it's own business. It's VHF doesn't work, and the speaker cloth is ghastly. But a friend of mine passed comment on it... "I've got one of those! Can you get it going for me?" Of course I can ....

Arrival. A few issues are immediately obvious. The case is cracked, the dial glass is broken, there's no pointer in the dial...

 Not much we can do about the crack, unless we fill it using car body filler, flat it and paint it up to look like bakelite.

Electronically, things are looking better...

 Chassis is removed and examined.

The on/off volume control is a replacement, but has worked lose, and has wrenched all it's wiring off, and the suppressor cap has long since exploded!.....







... Here's it's other end!

Plenty of horrible hunts. These have little cardboard sleeves, wrapped round little black caps, which interestingly have the value printed directly on the cap's body too!

The more traditional wax cap. They will all have to go!...

... as well as re-stuffing the electrolytic's where possible.

The mains smoother has been replaced in the past, with this expensive component! .... we'll see how it reforms....

... And after a few hours on the "Dreadnaught" capacitor reformer, it passes with flying colours, exhibiting correct capacity and acceptable ESR & leakage.

Case is removed....

 ... and given a bath

Chassis and dial is cleaned. Tuning is re-strung...

 ... and a dial pointer fabricated...

... capacitors changed, and electrically tested, medium wave and long wave working well, but no VHF reception....








VHF tuner is removed (a tedious job)...

 ... and a small decoupling capacitor is found to be electrically leaky (no surprise, it's a Hunts!) ... and VHF operation is restored...

 This radio also has a "gram" setting. This allowed connection of a record player (gramophone) back in the day. My friend wished to connect it to his iPod. The gram input was originally electrically isolated from the live mains chassis by some (now replaced) capacitors. Now in this day and age, I'm not happy with one side of the chassis being connected to neutral, and using this method to isolate a hand held device.

So I've fitted a small audio isolation transformer, which is eventually fitted to a bracket by the IF transformer. This is checked with a megger tester to confirm isolation from the mains.

Now all that remains is to re-assemble and sit back and listen!

Caroline ... on 319!!!

.... now I really should look at mine ....