Old Remcon off eBay...

[Dodgy Geezer]

Well. I've just picked up what looks like an old RemCon Versatile Transmitter - in what looks like a a home-brew box.

Seems to be all there, but doesn't seem to transmit (either that, or my radio is broken!). I don't suppose anyone has a fault-finding script? The Schematic in the Archive looks to be very useful, but there is only a set of test point voltages for the reciever, which I have not got.

Don't suppose I'll ever find a real old reed receiver - but it should not be impossin;e to make one. We just need a sheet of spring steel and a coil. Again, if someone gan give some suitable dimensions of a reed bsnk, that would be a great help...

DG

[Phil_G]

Hi Dodgy - its been a while
Theres the full constructional booklet on the Archive page of singlechannel.co.uk
https://www.mccrash-racing.co.uk/sc/dat ... satile.pdf

Do you have a comms receiver?

Reed banks appear quite often on ebay, there was an Otarion reed bank on there recently.
Cheers
Phil

[Dodgy Geezer]

Phil - good to hear from you! Pressure of work on my side. i'm afraid...

I saw the construction article with the schematic - unfortunately my fault-finding skills are non existent.... I tuned an SW radio to a 37mhz harminic, got a good signal and tone with an old MacGregor set, but not a peep out of the Remcon. Caps don;t look bad an soldering looks fine, so I suspect a transistor... unless it's a switch contact. Power seems to go through the main on-off switch...

I haven;t seen a reed receiver on ebay ever. Maybe I just don;t have the right search string...I would certainly like to pick one up - 12 channel ideally¬

DG

[Phil_G]

Transistors would be last on my list Dodgy, I suspect its not oscillating, try another crystal, measure the crystal osc supply volts, its very likely an electrolytic has gone, maybe all of them. Drape your rx aerial around the crystal, you should pick up a carrier if its oscillating (ie the radio hiss will quieten)
The tone generators (2 of them) and the RF are separate & can be checked separately.
You really need some test gear, I wouldnt try to knit a jumper without knitting needles

[Dodgy Geezer]

Don't think there are any electrolytic on the board - I would have suspected them if there were..

I do have a multimeter and a scope - the question is what to do with them! The only testing I have done so far is to listen for the suppressed hiss and tones from the main aerial - which aren't there. The archive document talks about using a lightbulb...

I do have a spare crystal. Do they really fail? I thought they were quite robust..

[Pchristy]

Fault finding on any electronic gear - but particularly transmitters and receivers - requires a degree of basic know-how, plus some test gear and knowing how to use it. Phil has already alluded to this, but it bears repeating!

Having said that, a multimeter and a 'scope is a good starting point!

Always start by checking power supplies. This means not just checking that it is the right voltage, but is it getting to where it is required. This is where the multimeter comes in.

Is the power getting beyond the switch? Is it getting to the various oscillators and amplifiers? If you have downloaded the construction articles, they should give a clue as to where to look with the multimeter set to volts.

Next, is it drawing any current? Set the multimeter to a high current setting (say 300-500mA) and insert it in series with the power supply (battery). When you switch on, does it show any current? Try gradually reducing the current setting on the multimeter. I would expect the crystal oscillator to be drawing around the 10mA mark. If the output stage is also working, this should be in the 100mA or so region. Does this change when you key any of the switches? It should, as the audio oscillators should start drawing current.

If it isn't drawing anything at all, then start looking for open circuits, starting with the switch and then the crystal oscillator (change crystal, as per Phil's suggestion). If the current doesn't increase when the keys are pressed, then the audio oscillators aren't working and need checking.

This isn't a comprehensive list, but should get you started. Once you've gone through that lot, report back your findings, and we'll see if we can guide you further...

--
Pete

[Dodgy Geezer]

Pete,

Thanks very much for the direction!

I had tried those actions earlier. the switch passed 11v through, but I couldn't detect any current - even at a 2ma setting.

I had no easy 12v source, so am using a 9.6Nimh. Just charged, it reads 11v, and it drives a Taycol motor well, so I have adequate power. I have checked that the switch lets power into the pcb lands, but am unsure where to go from there. I didn't want to remove the PCB from the case if I could help it - but I suppose I'll have to if the next step is changing the crystal. It's a 27.045. I wonder why all the Txs seem to default to red...

The tones all seem to be set by 1k slider pots mounted on the back of the board. They are likely to be open circuit - I shifted each slide a bit to get them onto a new bit of track. Most worked, but 4 of the pots look to be open circuit. I don't know what effect that will have (and whether I can mend them or find replacemets)...

[Phil_G]

Do you have a crystal earpiece Dodgy? one of the handiest test tools!
Holding the barrel of the 3.5mm jack plug, touch the tip on the hot end of R9,
When keying the toggles you should hear the tones in the earpiece.
There are two audio oscillators, it would be bad luck if both had gone faulty

I have a soft spot for the Remcom 12 as my Dad built mine, but its an awful design to be honest.
No supply regulation, voltage-sensitive astable multivibrators, crappy slider pots... now compare that with an Orbit

[Dodgy Geezer]

I have no earpiece. but have just ordered one - it looks a lot easier than lugging a big Gould oscilloscope down from the loft at my time of life...

However, the tone generators are connected to the switches, which seem to have innumerable contacts - all of them potentially dirty. It will be a big job just to clean them! Since I didn't get the radio hiss suppression when powering up, I'm inclined to look for the carrier wave, and change the crystal first... Though I notice that there IS one electrolytic which will probably need replacing as well. Or at least removing and testing...

[Phil_G]

Ah sorry I thought you'd already tried another crystal.
Its obviously an RF problem but I thought that finding the tones generators worked might be a confidence boost.
I would change the electrolytic anyway, its 50 years old and they cost pennies.
If the toggles are the original ones used by Remcon (loud clicky ones) then they're sealed, they're usually ok.
The lack of stability meant that many users modified the power rails - check the 'quality' of any mods, could be
as simple as just a resistor & a zener - though that would normally be after the osc & PA.