Friday, 22 August 2014

Stalled, the workshop has had to be packed away for family parties and visitors.

But, coding on the laptop continues so a brief outline of plans.

The Cobra uses a rotary encoder for channel select and a CPU that 'listens' to it, incrementing the N-Codes to the PLL or decrementing as necessary, controlling the channel display and mode indicators etc.

Pressing the WX button while the radio is powered up allows you to choose a weather channel on the WX sub board so that seems ideal for a band switch.

Or, I could just 'keep going', when it hits 40, the channel display rolls over to 1 but my PIC carries on up to Hi band or from 1 to 40 Lo.

I need some kind of indicator to tell me where I am, perhaps coloured LEDs behind the LCD...

All things to think about and suggestions are welcome.


Friday, 15 August 2014

And here we go

Parts arrived, a nice clean crystal and a N.O.S. MB8719 to be transplanted into the radio.

So, in goes the crystal and immediately it springs into life on channel 1 mid, 26.961MHz, a tad out of alignment I'd say.

Fortunately there's a lot of information on these radios, there's even a full service manual for the Ranger TR-296 which uses the same board, EPT014811Z but has different arrangements for channel display and change.

A few quick tweaks later and it's on frequency, RX and TX, power is a shade under 4W into a dummy load.


Next step, pop out that cracked front bezel.
Quite a battle to do and the picture makes it look worse than it is. I'm satisfied with the appearance, it looks like a scratch.

Next up, fit the MB8719 and see how far I can make it go before the VCO etc. runs out of steam.

I'm hoping to get Lo, Mid and Hi without having to 'wide band' the VCO etc.



Saturday, 9 August 2014

Surprise!

A little more work, the mains transformer is a 110V unit, obviously needs replacing for use in the UK so I unbolted it.

Hidden underneath, another serial number plate.



Friday, 8 August 2014

Muwahahahahaha

A crystal arrived in the post today, 11.285MHz, soldered it in, a couple of quick tweaks later and we have:

OK, so it's a few channels out but it's meant to have an 11.325MHz crystal in there.

It works.



Thursday, 7 August 2014

Progress

11.325MHz crystal and an MB8719 on the way to me.

Broken wire carrying 8V to the mode switch had snapped off so remaking that connection restored the AM/USB/LSB display.

The 'Voicelock' or clarifier is now relocked although it's a dual control so I may fiddle with that again later so that one pot tracks RX, the other TX.

The AMC had been disabled by clipping R131 so that's been replaced.

I can't find R175, 8K2 on the board so for now (and probably permanently) I've added it to the Voicelock control.

From this:
To this.
Next step, wait. Patiently.

Then fit the proper loop crystal and see if I can get the VCO to lock.I can't see any other mods or bodges on the board, at least not so far.


Friday, 1 August 2014

Cobra 2010GTL WX

One of the new arrivals, a Cobra 2010GTL WX, 40 channel AM/SSB homebase radio.

I bought it with the intention of transplanting 'something' into it but also because it was a good price and I was curious about the WX part of it.

I was told it was complete, that it had a few problems, not least that the CPU was blown. There's a cracked front bezel which looks not too difficult to push back, a hole drilled in the lid and the lid has been sprayed a metallic blue (badly)

So, when it arrived of course I had to take it apart and inside I found an EPT0014811Z board that's actually in really good condition. Same board as the Cobra 148GTL.

It's been messed about with, first glance showed there were wires floating loose inside, components clipped, a missing loop oscillator crystal (11.325MHz, have you got a spare one you would like to send to a good home?)  and probably other non obvious mods but it looks good. Worth spending some time on.

Now, call me a contrarian, obstinate, awkward, whatever you want but I like to prove things for myself so I set about seeing if I could fix the biggest game killer and removed the CPU board, immediately seeing a burned track and some dodgy soldering.

After replacing a shorted 1N4148, D203, and remaking the burned track the display sprung into life, channels changed up and down but no TX and the mode display didn't change, it was stuck on AM.

But, this is partly why I'm obstinate, it doesn't have a blown CPU.

More to come soon.

A few pics:
 Not too bad, not mint in box.

 Missing loop crystal and an RCI8734, that'll need replacing with an MB8719 or with a little extra work, MC145106 so I can get it onto Lo and Hi without needing lots of crystals.
  Working display (yes, showing LSB, I fixed that too, more in the next post)

Thursday, 31 July 2014

Stalled.

Well, sometimes real life gets in the way of fun.

Fear not though, the Dog is still alive and is on the 'To Do' shelf..

I'm still looking for a set of cases and a front. Oh and knobs.

But, for now, well it seems the bug has bitten again so I'm building up a workshop, test equipment and components.

Test equipment now:

Sayrosa/Farnell 257 AMM
Hameg Analogue Scope 30 something series.
Thandar TFM600
Three variable bench PSUs, two dual channel, one single.
AD8307 based power meter.

I've also got regular access to a spectrum analyser now too.


There have been a few radios purchased, Cobra 2010 GTL WX base station which could be really nice, a MK2 Jumbo PTBM121D4X, Magnum 257, Magnum Deltaforce, another Cobra 148TL DX, Lafayette 1200, couple of Ham Vikings and a pile of lovely scrap chassis' for parts.

So, onwards, if I ever get time to sit down and concentrate on 'The Dog' I'll post updates here,  until then expect random posts about other radios and related bits n'pieces.

A brief update on the DDS board though, once the output signal was buffered, it worked beautifully as a crystal replacement, I need to manage USB/LSB offsets in software but it will make tune up of the radio beautifully simple and remove a lot of the hair's breadth alignment that needs to be done on these radios. It also tunes in steps as small as 1Hz. Which is nice but a little impractical for day to day use.