Help Power Supply 3.5" Floppy

discuss both original and modern hardware for the bbc micro/electron
Post Reply
mogouk
Posts: 19
Joined: Fri Jul 15, 2011 10:26 pm
Contact:

Help Power Supply 3.5" Floppy

Post by mogouk » Sat Apr 14, 2012 5:08 pm

Hello all, any idea what sort of power supply i should try for this bbc 3.5" floppy?
i dont wanna be smelling burnt electronics lol.

Thx in advance!

mogouk.

ive uploaded a 2nd photo of the power board inside.
Attachments
photo2.JPG
photo2.JPG (172.05 KiB) Viewed 1632 times
photo.JPG
photo.JPG (131.66 KiB) Viewed 1642 times
Last edited by mogouk on Sat Apr 14, 2012 5:33 pm, edited 1 time in total.

User avatar
AndyF
Posts: 1276
Joined: Sat Feb 23, 2008 10:16 pm
Location: Derby
Contact:

Re: Help Power Supply 3.5" Floppy

Post by AndyF » Sat Apr 14, 2012 5:21 pm

I'd whip the lid off and have a look, you may find a couple of 78x series voltage regulators. Although I seem to remember (not sure) the 3.5 drives did not really *need* a +12v supply.

I'd look inside to see what's there, it might have a bridge rectifier as well in which case it would want a low voltage AC supply.
Andy

* NEW * The Jetset Willy and Manic Miner community :)

Adventure games ported across to the BBC (in progress) as soon as I can find some time!

mogouk
Posts: 19
Joined: Fri Jul 15, 2011 10:26 pm
Contact:

Re: Help Power Supply 3.5" Floppy

Post by mogouk » Sat Apr 14, 2012 5:51 pm

thanks for the reply andy, im not up on electronics, so you've lost me, ill up a better photo to help more.
Attachments
photo3.JPG
photo3.JPG (185.54 KiB) Viewed 1627 times

johnkenyon
Posts: 253
Joined: Wed Jul 20, 2011 3:21 pm
Location: Coventry
Contact:

Re: Help Power Supply 3.5" Floppy

Post by johnkenyon » Sat Apr 14, 2012 6:49 pm

Looks like the connector to the drive only supplies +5v to the two outside pins, so assuming it's a 7805 regulator a 9v DC unregulated supply should do the trick.

As far as current is concerned, find out what the drive needs (google the drive model number may help).

As far as "tip positive or negative" I suggest that you trace the PCB track from the jack input and see whether the tip or barrel goes to the pin marked "IN" on the PCB.

If you were feeling brave, you could snip the regulator out, put a jumper between the pins marked "IN" and "OUT" and use a 5v 1A USB charger. (you may have to look out for a 1A charger, because most of them are rated at 500mA)

/john

mogouk
Posts: 19
Joined: Fri Jul 15, 2011 10:26 pm
Contact:

Re: Help Power Supply 3.5" Floppy

Post by mogouk » Sat Apr 14, 2012 8:38 pm

Thanks for the feedback john, just tried a 9v DC 500ma power supply, but its not responding, it does get a little warm though!

User avatar
MartinB
Posts: 5353
Joined: Mon Mar 31, 2008 10:04 pm
Location: Obscurity
Contact:

Re: Help Power Supply 3.5" Floppy

Post by MartinB » Sat Apr 14, 2012 9:29 pm

The standby current of most 3.5" drives is very low and the average operating current is around 200-300mA. However, there are peak demands such as motor start and head step which can easily exceed 500mA. Thus, when you power up your drive, it will likely try to move the drive spindle and/or head as it initialises and this will then cause your supply to fold when it can't handle the peak demand. The drive will then start to power down, your supply will come up and so the circle continues. All this rapid power toggling will result in nothing much happening beyond your PSU getting warm :wink:

I would therefore concur with John in that you need to try a 1A PSU that can cope with the transient peak demands before passing judgement on the drive's serviceability.

mogouk
Posts: 19
Joined: Fri Jul 15, 2011 10:26 pm
Contact:

Re: Help Power Supply 3.5" Floppy

Post by mogouk » Sat Apr 14, 2012 11:14 pm

Thanks for the reply MartinB, ive just tried a DC adapter 9v 1000ma still no joy, maybe somethings blown???

User avatar
MartinB
Posts: 5353
Joined: Mon Mar 31, 2008 10:04 pm
Location: Obscurity
Contact:

Re: Help Power Supply 3.5" Floppy

Post by MartinB » Sun Apr 15, 2012 12:15 am

mogouk wrote:...maybe somethings blown???
Not necessarily. If we assume the drive is now being correctly supplied with 5v, how do you have it connected to the Beeb or Master (?) and what are you doing to determine whether it works or not? Is it a Beeb-specific drive unit? Which disc interface and DFS do you have fitted? Is the unit configured as Drive 0 or 1 and have you tried both - i.e. tried *DR.0 and *DR.1, both followed by a *. ? When doing the latter, does the drive access light illuminate? Does it do anything at all? (Sometimes you can hear the disc shutter being withdrawn when you insert the disc.)

More information about your 'no joy' in the first instance. You get the idea.... :wink:

mogouk
Posts: 19
Joined: Fri Jul 15, 2011 10:26 pm
Contact:

Re: Help Power Supply 3.5" Floppy

Post by mogouk » Sun Apr 15, 2012 11:04 am

ok heres where im upto, i tried the floppy in another case with auxillary power and it works fine on my model b and master, thanks to martin b for mentioning drive 1 as i was just testing as drive 0 :oops:

i have now set it back to Drive 0 for testing purposes, with a 9v DC 1000ma adapter i can get the access light to come on when i do a *CAT but it wont list contents nor will it boot from any disk it does this set as drive 0 and drive 1, pressing SHIFT BREAK the access light comes on but does not read disc.

with the auxillary power it clicks and functions as it should maybe it needs a bit more juice a 12v supply maybe??

User avatar
1024MAK
Posts: 10361
Joined: Mon Apr 18, 2011 5:46 pm
Location: Looking forward to summer in Somerset, UK...
Contact:

Re: Help Power Supply 3.5" Floppy

Post by 1024MAK » Sun Apr 15, 2012 11:30 am

Given that the power supply PCB in your floppy disk only has the single regulator chip (presumed to be a +5V 7805 type), you may need to use a regulated +12V 1A power adaptor / PSU.
This is because some (older) 3.5 inch drives need a +12V supply as well as a +5V supply.

Mark K.

mogouk
Posts: 19
Joined: Fri Jul 15, 2011 10:26 pm
Contact:

Re: Help Power Supply 3.5" Floppy

Post by mogouk » Sun Apr 15, 2012 12:14 pm

BINGO! Thanks to 1024MAK and all who replied in this thread =D>
Drive working fine now with a 12V 1A supply, i used a Netgear Modem power supply its all that i had, its been on now for half an hour, drive and power supply are cold to the touch!

User avatar
MartinB
Posts: 5353
Joined: Mon Mar 31, 2008 10:04 pm
Location: Obscurity
Contact:

Re: Help Power Supply 3.5" Floppy

Post by MartinB » Sun Apr 15, 2012 12:38 pm

Lol - I'm glad you got it working but I haven't a clue what just happened :-k

(I presume you still only have a single rail supply?)

mogouk
Posts: 19
Joined: Fri Jul 15, 2011 10:26 pm
Contact:

Re: Help Power Supply 3.5" Floppy

Post by mogouk » Sun Apr 15, 2012 1:07 pm

MartinB wrote:Lol - I'm glad you got it working but I haven't a clue what just happened :-k

(I presume you still only have a single rail supply?)

like i said i aint up on electronics so single rail supply you've lost me???

will the power supply im using be ok long term/saftey wise?

link to power supply im using: http://www.ebay.co.uk/itm/NETGEAR-WGPS6 ... 8535915692

User avatar
MartinB
Posts: 5353
Joined: Mon Mar 31, 2008 10:04 pm
Location: Obscurity
Contact:

Re: Help Power Supply 3.5" Floppy

Post by MartinB » Sun Apr 15, 2012 1:25 pm

Heh - don't worry, you're not doing anything wrong, the outcome is just a bit confusing. I presume that the drive power connector being labelled 5/0/0/5 is misleading and that there is actually a tap from the 'raw' DC input to one of the supposed 5v connections. Thus, by using a 12v supply as your primary source, the drive is now getting 5v from the internal regulator and 12v directly from the input supply. Simply upping the source supply from 9v to 12v didn't make any sense unless the above assumption is true.

So, no need to worry, everything is fine now :D

mogouk
Posts: 19
Joined: Fri Jul 15, 2011 10:26 pm
Contact:

Re: Help Power Supply 3.5" Floppy

Post by mogouk » Sun Apr 15, 2012 1:55 pm

Thanks for replying Martin, just dusted off my test meter, read the following DC voltage going into regulator 16.55V, 4.98V coming out of regulator, 4.98V going to both ends of floppy connector.

im confused again now as i thought the auxillary power connector was sending 12V as well as 5V??? i thought all floppies needed 12V?

User avatar
paulv
Posts: 3854
Joined: Tue Jan 25, 2011 6:37 pm
Location: Leicestershire
Contact:

Re: Help Power Supply 3.5" Floppy

Post by paulv » Sun Apr 15, 2012 2:16 pm

im confused again now as i thought the auxillary power connector was sending 12V as well as 5V??? i thought all floppies needed 12V?
Floppy drives in the Acorn BBC A3000 only have a 5V and 0V connection as do other machines.

WRT to needing the 12V supply voltage, the 5V regulator usually has a certain input range that it will accept before outputting a good steady 5V value. It would seem that your 9V supply must have been borderline or just below the lower limit to make the regulator work reliably although according to the data sheets I've read a 7805 regulator should be okay with 9V as their suitable input ranges are around 7V to 25V.

Paul

User avatar
MartinB
Posts: 5353
Joined: Mon Mar 31, 2008 10:04 pm
Location: Obscurity
Contact:

Re: Help Power Supply 3.5" Floppy

Post by MartinB » Sun Apr 15, 2012 2:23 pm

Ok, so it's a 5v only drive which is true of all later 3.5" drives. Only 5.25" and early 3.5" drives needed 5v and 12v.

My confusion then is why the 12v adaptor (clearly an unregulated unit given the 16v output) should be required over the 9v unit. The internal 5v regulator (bolted to the back panel) needs just over 7v to regulate and produce 5v so the 9v 1A unit should have been just fine. As John alluded to earlier on, I wonder if the polarity of all your PSU's is the same. Just out of interest, try your meter on the output plug of the 12v and 9v units and see if the centre recess of the plug is positive and the metal outer sleeve is negative (or vice versa.) If they are different, that might explain why the 9v unit didn't work.

A 9v PSU would be preferable because the higher the input voltage, the harder the regulator has to work to dump anything over 5v.

Edit : Sorry Paul, obviously typed that while you were replying!

mogouk
Posts: 19
Joined: Fri Jul 15, 2011 10:26 pm
Contact:

Re: Help Power Supply 3.5" Floppy

Post by mogouk » Sun Apr 15, 2012 2:46 pm

your assumptions were right MartinB the 9v adapters i tried were different polarity to the 12V 1A one.

Thanks again for showing interest, just been reading a few datasheets on things i've got a lot to learn lol.

Post Reply

Return to “8-bit acorn hardware”