The 'Cool' Tangerine Microdrive for ORIC1 & ATMOS

For some internal Photo's including stripping the 3" Drive unit to clean the Head properly please see this Media Library https://atari-owner.com/club/media/albums/oric-microdrive.4/

I'm sure if you are an ORIC or ATMOS owner, that you are aware they along with the Micro drive run a 'bit' warm, there have been a few thoughts as to why, one which is fairly commonly mentioned is that the original power transformers were the same as those used in Europe being 220V rated and not the 240V seen in the UK. the difference is very close to 10% and to be honest doesn’t really account for the very high DC voltages I've seen output from the Oric’s Micro drive PSU (I’ll add I don’t yet own either but I have been working on a Microdrive unit to alleviate the temperatures it gets too)

The power brick supplies 21-22V, to be regulated to 12V and 15-16V for the 5V Rail the same approx 15V is sent to the computer itself, hence why they run so hot as approx 2/3's of the power is converted to Heat.

These high voltages are then fed to the Micro drive unit and the 12V & 5V levels required are regulated within the Micro drive case itself, the additional voltage causes the Micro drive to warm up and many have said this is the cause of the 3" drives being so unreliable.

Using commonly available linear voltage regulators, for both the Oric and the Micro drive means they will have to dissipate the heat they produce.

We can work out how much with a simple bit of math. Power = Volts X Amps.

Input voltage 15V x 1.6 A (the current draw) gives 24W
Voltage required is 5V so 5V x 1.6A = 8W
The excessive voltage supplied causes the regulator to dissipate 16W as wasted heat.

The 12V rail is similar however as 12V is only used very intermittently for the motor in the floppy drive it’s current pull is very low unless the drive is in constant use, so although it wastes heat the effect is very small in comparison.
22 x 1A = 22W 12 x 1A = 12W 10 W however it’s usually a current draw of about 150mA

22x 0.15 = 3.3W 12V x0.15 = 1.8W so about 1.5W continuous heat , but when the motor is spinning a disc, 10W

Modern Switch mode power supplies and regulators are very much more efficient, and using a high switching speed also reduces the amount of smoothing capacitance required.

The replacement for the 5V regulator (original LM323K in a TO3 case) able to source 3A, was purchased from the USA, and has been purposely designed for the arcade gaming industry as a direct replacement.

It’s able to be used at its fully rated current load of 3A without the use of any heat sink

The 12V regulator is based on a common 7812 type device a LM340T12 in a TO220 package, I used the same switching regulator as the 1088XLD uses and again high speed switching internally means no additional smoothing capacitors are required.

Both items are direct replacements for the originals, and are the two items mounted on the rear heat sink of the Micro drive.

On the Transformer ‘Brick’ although I did shorten some leads from this and remove the additional one for a second Micro drive. I also changed the wiring to the LED on this as internally was likely to short across one of the bridge rectifiers within.

The two Items I’ve used are

5V EzSbc.com LM323K replacement
https://www.ezsbc.com/index.php/products/psu5.html

12V Texas Instruments TPSM84212EAB
https://www.digikey.co.uk/products/en?keywords=296-47075-ND

I'd like to Thank Andy Barr for loaning me his prized possession to create this Post.

 

Graham,
The pleasure has been mine throughout so thank you sincerely for all the work, research and time you've put in.
Let's hope Richie makes a breakthrough this week with a possible replacement 3" donor disk drive to finally bring this excellent work to a fruitful and working conclusion soon!
Cheers, fellas once more for a whole load of great collaborative work from you and Richie.

 

HeHe Well it's Richie that proved the drive was faulty, and I guess why you have had so many problems over the years, however I really hope they guy pulls through with a drive, that way you can use your original disks alongside your Gotek.
I'd imagine after all these years having it work properly will be a godsend.. Mind you I've got to find you a DDI yet the last one I saw went for over £300 so Ditch the 464 and get a 6128. or a Spectrum +3 (cower)

 

LOL! Many thanks, Graham - you've both been fab with all your help and technical advice as the microdisc had just become an expensive paperweight here and would've just been sold on as "spares and repairs" at some point. Now there is every chance the old gal will read and write 3" disks again - maybe!
As for your Amstrad advice, NO! I don't wish to go down any more 3" disk drive roads - the Oric one's bumpy enough!
I'll stick to my trusty tapes and basic CPC model - for now, fella!!
Cheers, Graham.
;-)

 

You can get an expansion for the 464 called a DDI3 which plugs in the expansion port and gives you a Gotek drive and an IDC connector for a second drive.

 

That seems a nice device.
Shame it's limited to CPC's with an edge connector, as the CPC's with a centronics connector, or MX4 motherboards have been left out, so that's it, no memory upgrades or extra ROM's with what now has become a standard way of extending all CPC's via MX4. I guess it could sit on the very end of the MX4 backplane(the type with an edge connector) but; anything plugged in the MX4 connectors in front could obscure the LCD display.
I'm sure that allowing for three type of connector could have been included, even just 2 would have been better.

Currently just under £60

 

You can get a version with 512KB RAM PCB fitted to expand the 464’s memory. There is a Centronics to Edge connector out there somewhere.