The Dragon 32. New Power supply, New Century

[@KeritechElectronics]

Lovely power supply! Keep the old one, in case you want to restore the unit to its original state. Apart from the strange dust (almost reminding me of asbestos, but I can't see a way that crap could end up there, especially on pots only), there was hair inside too - I'd blow some compressed air at it. LM309K is a linear regulator, a counterpart of 7805 in a TO-3 package. It will dissipate power equal to (Vin - 5V) * I, which means the higher the input voltage and the higher the current, the more heat it dissipates and the lesser its efficiency. Modern switch mode power supplies run at 70% efficiency at least and the losses are proportional to output power rather than input voltage. That's why I used a switch mode counterpart of a 7805 in my Commodore 64 supply that I built into the original enclosure.

[@techdept]

Don’t worry. I always keep the boards that get replaced, just in case. And thanks for the tips sweetie. Much appreciated. :)

[@dmcmoose]

That video was proper tidy! Diolch yn fawr.

[@techdept]

Diolch indeed. I really do love the old dragon. And I had a lot of fun playing a few old games once the camera was off. Pub crawl was a weird one!

[@8bitsinthebasement]

I enjoyed your look at the Dragon 32, I've never used a "real" one but I have put in a lot of time behind the old Coco 2. If you wanted to you could make or buy an Atari to Dragon/Coco joystick adapter or buy a Dragon analogue joystick (the other option is to convert a PC analog joystick to work with the Dragon, shouldn't pose a problem to someone who can solder). Then you could play all the great games that the Dragon has to offer. Keep up the great work. Subbed I have :)

[@CaptainCommodore]

The dragon 32 was my first computer as a kid ( briefly before I got a commodore ) I have a lot of affection for these machines and it really is a strange hybrid of a superb cpu and crap graphics chip...... I too have done the psu to mine ( think I did a vid on it too ) The video output on a dragon is universally diabolical, and that's largely because the video signal is bastardized ntsc which is mercilessly hammered into being PAL...... an interesting side effect is the phase based artifact colours, I severely recommend using a RGB2HDMI with the dragon for perfect video........

[@techdept]

Yeah I’m thinking I’ll add the RGB2HDMI to the machine. It’s such a weird but cool computer.

[@julianbrown1331]

The furry resistors are common to all machines - it comes back fairly quickly but doesn't seem to be anything more than a cosmetic problem. The boards are actually quite robust - I've only had one that lost a pad out of "a lot" of repairs for other reasons (mostly memory). That said excess heat will delaminate the board same as any other (ask Andreas Zahrl about his D64 - that took some serious fixing). The *only* parts on that board that are problematic to obtain are the SAM, cartridge port and the VDG. There is a modern replacement for the SAM, I'm working on a modern replacement for the VDG and there are compatible parts for the cartridge port but they lack the mechanical fixings (or cost a small fivetune to obtain due to minimum order size)

[@julianbrown1331]

Forget to mention the LM1889N modulator in that list of problems - plenty of them in dead spectrums but then the chip tends to be dead too. The lack of colour initially (when the voltage is low) is likely to be the modulator failing to build the PAL signal properly - the +5V and -5V need to be pretty closely matched otherwise it all goes either very muted (low -5V), fails to run at all (low +5V), or it just fails to drive the crystal for the carrier frequency. The DragonPlus RGB board bypasses the modulator, as does my VDG replacement

[@techdept]

Awesome explanation Julian. Again I really appreciate the insights you have with the Dragon. Please keep in touch with updates to your projects. I’m really interested in seeing how you do.

[@sandmehlig]

I would have gone my usually panicky route and try to re-solder the sound chip (and messing up everything on the way). 😅

[@techdept]

I tend to get confused at first if something screws up, before getting weirdly methodical in testing all the things. Mostly though I just need time to work the problem before I find the cause and/or a solution. :)

[@julianbrown1331]

One more thought on the voltages - I've never seen it comes back from a failure but the final part of the video circuit typically has 3 transistors in it (TR2,3,4) that in failure mode nearly bridge +5V to -5V. There is always a resistor in the circuit so it should never bridge completely. The side-effect of a failure is the +5V rail drops to about 2.4V. Annoyingly some of the boards came with an op-amp instead of the three transistors and I didn't clock which version of the board you have

[@techdept]

I will check and get back to you. But I do I know it’s an issue 2 board with a low 5000 something serial number.

[@julianbrown1331]

@@techdept That means it could be one of three different designs... OKI32, Siemens32 or SA2120

[@djwilduk]

Funny the furry pots there... I have a few BBC Micros and the analogue port connector (only) also suffers from white fluff. Perhaps a certain type of plastic grows fur over time. Best wishes, Dafydd.

[@rickyelqasem]

I like you said “we make robots “

[@techdept]

Yeah, it had been a long 72 hours prior to me recording the voiceover. A lack of good sleep was definitely showing.

[@YouMakeRobots]

if you purchased the sd box it in the last 6 months it will work with your MSX with reflashing if you set the baud to 3600 not 3850 ... Also supports Sinclair, Amstrad, Coco and a bunch of others..

[@techdept]

Thanks for the update. I’ll check it out to make sure which version I have. But it’s a great but of kit. That extra preamp makes a difference. :)