[Premium-Rx] RA1792 displays

Wed Aug 11 08:30:13 EDT 2010

Hi all,

I'm not sure if it's fully in the group rule book so to speak, but if 
anyone fancies a third option, not sure why you would really but there 
you go, check out my website at www.ra1792.co.uk for a RA1792 DIY 
display kit.
I personally would go for the ra1792lcd.com replacements, but these were 
not available at the time I started work on the kit.
My kit is of a similar design to the Italian replacement kit, using of 
the shelf 16x2 displays and a PIC micro controller. It is not a copy of 
the Italian kit as has been suggested. I did not even know that the 
other kit existed until I published my design and received feedback 
about the other kit.

You should be able to build my design for under £20 all in, so a little 
cheaper than the other kit, although I acknowledge there's is a lot more 
polished....

Cheers,
Dave.S.
Sorry again for the plug :-)

David Bobbett wrote:
> Hi France,
>
> Nope, nothing anywhere near as sophisticated as that for the 
> backlighting! Each display is lit using 16 series/parallel wire-ended 
> filament bulbs mounted on a small PCB which is then screwed into two 
> mounting bushes set in the PCB behind the front panel. Each bush acts as 
> the connection to feed about 9v AC from the PSU and the brightness of 
> the display can be varied by changing the two wirewound resistors which 
> you will find on the front vertical face of the PSU. The bulbs are 5v 
> 60mA T1 wire-ended types and are still available.
>
> In my case, I converted an early non-backlit 1792 to a backlit version 
> as I had some spare front panel and backlighting PCBs left over from the 
> junk pile. The PSU is the same in either version and only needs a bit of 
> re-wiring and the resistors to get it to work -  some mods  to front 
> panel PCB are needed, but that's another topic.
>
> A white plastic diffuser is stuck to the rear of each LCD using two thin 
> strips of double sided sticky tape (although this has usually come loose 
> over the years) unless some genius has epoxy glued it back on as I found 
> with a couple of 1792s which I refurbished. The epoxy also ruins the LCD 
> over time, so it was not a good plan, although getting some replacement 
> diffusers cut shouldn't be a problem if this has happened.
>
> Easiest method seems to be: sit radio with front panel uppermost, remove 
> knobs, front panel screws and the front panel itself; you don't have to 
> remove the inner black front panel. Gently lever out the old LCDs by  
> inserting a screwdriver under the top left hand corner and lifting the 
> display slightly, then do the same to the bottom left hand corner, top 
> right hand corner and bottom right hand corner. The objective is to just 
> loosen the display at this stage, then work around until the display 
> comes free. You will then probably find the diffuser sitting on top of 
> the backlighting pcb. If you've got good diffusers, clean them and 
> remove any tape residue with iso-propyl alcohol (propanol) and put to 
> one side.
>
> Undo the cross-head screws which secure the backlighting PCBs and fire 
> up the soldering iron. Although it is a chore, I would recommend 
> replacing all the backlight bulbs because a) you will get more even 
> illumination and b) the old bulbs tend to suffer from wire oxidation 
> which causes intermittent bulb failure. When you have finished replacing 
> all 32 bulbs it is worth soak-testing the boards for 24 hours by fitting 
> them without the LCDs in place - you need to avoid having to remove and 
> refit the new LCDs if you can as their pins are a bit fragile.
>
> The new LCDs have a tough clear plastic tape over the rear of the 
> display, remove this by gently pulling slowly upwards at 90 degrees to 
> the back of the display, reduce the strain on the LCD by placing a 
> finger just in front of the line where the tape pulls away the display - 
> you have to be rather careful! Once that layer is removed, do the same 
> with the backing for the silvered finish and very, very gently rub off 
> the remaining silver layer using cotton buds and a dish of methylated 
> spirits. I put a pad of kitchen paper in the bottom of the dish to avoid 
> damaging the front face of the LCD and this last process took me about 
> an hour for each display. Don't be tempted to press too hard though, as 
> you can mark the back of the LCD that way. At the risk of stating the 
> screamingly obvious, no smoking or naked lights and make sure that you 
> have plenty of ventilation when working with methylated spirits.
>
> Assuming that you have finished this process and still have your sanity, 
> its time to fix the diffuser to the new display. The method I used was 
> to carefully centre the diffuser against the back of the LCD and secure 
> it using clothes pegs - use a piece of folded paper or card to protect 
> the front face from the pegs. I then ran a thin bead of hot-melt glue 
> along each end of the assembly where the diffuser meets the LCD; you 
> don't need very much and hot-glue is fairly inert so if you muck the 
> alignment, the glue can be scored with a very sharp knife when cool to 
> break the seal and have another go.
>
> The LCD sockets on the main chassis are actually two or three strips of 
> DIL socket material sat in a row, so it is wise to check that the new 
> display legs will line up correctly, a certain amount of judicious 
> socket bending may be required before the LCD will fit easily. A quick 
> squirt of switch lubricant/cleaner should be applied to the sockets and 
> the LCD pins (removing any excess of course) to help things along before 
> installing the displays. Check that the LCD is the correct one and the 
> right way up before inserting the new display. All that is left to do 
> now is to switch on the radio, check the display, remove the protective 
> film from the front of the LCDs and tell yourself that you never want to 
> do that again! If you are like me, you will probably want to clean and 
> wax the front panel before refitting it, but don't forget to clean the 
> rear of  the yellow filters before re-assembling the radio.
>
> As for choosing which display upgrade to go for, I did see the retro-fit 
> kit which Hienz was kind enough to mention, but at 200 Euros (vs a 50 
> euros for the LCDs I used) I thought it was overpriced when you consider 
> that a 1792 sells for between £200 and £450. The kit is only a pair of 
> industry standard 2 line by 24 character displays and a CPU, so that 
> strikes me as being expensive - but perhaps I am just mean! Also, I 
> didn't like the idea of having another microprocessor and its crystal 
> oscillator installed inside the radio as I would be concerned about the 
> spurii from such an arrangement. On the positive side, it looks as 
> though the kit already has backlighting and should be quick and easy to 
> fit, so I suppose it is a question of which you prefer.
>
> Apologies for the 'War & Peace' posting, but hopefully this info will be 
> of use to fellow 1792 users.
>
>
> 73 de David, G4IRQ
>
>
>
>
>
>
> On 11/08/2010 09:23, fantelme2 at comcast.net wrote:
>   
>> Hi David,
>>
>> . . . I presume that the backlighting is done with  electroluminescent 
>> panels, not having dismantled the front panel to actually take a look. 
>> At the risk of being a nuisance, do you know if there are replacement 
>> backlighting panels available?
>>
>> Thanks once again for your time
>>
>> 73
>>
>> -France K6QO/ZS6GO-
>>
>>     
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