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Floppy Voltage Regulators

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I have another hardware/electronics query.  This is Percom-drive related (to me) but not specific to them.

 

So I recently became aware of those DC/DC Converter --  Buck Regulators -- Switching Voltage Regulators.  All the same name for the same thing I guess?  I mean the ones that are drop-in replacements for the 7805 and 7812 specifically.

 

Since the Percom drives all have problems with regulator mounting / heat issues / etc. I thought that maybe using these drop-in replacements would be a good idea.  Pros are that they are very electrically efficient, and don't generate much heat.  Cons are that they are a bit expensive, and do generate some electrical noise.

 

Would using these in floppy drives be a good idea?  Has anyone done this?  I wonder if the noise factor would be an issue with the floppy writing/reading, etc.  I don't have an O-Scope, and I'm just a "minor" electronics guy, so I was wondering if someone with more experience in that area could chime in.  Thanks!

 

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I know people have used them successfully in 1050’s, so the concept is sound. I spent time this past summer restoring a Sinclair ZX81 and its twin, a Times-Sinclair 1000. These machines use a 7805 mounted to a massive heatsink - inside those tiny, sealed cases it gets very hot! I replaced the 7805 in each machine with a Traco equivalent and not only do the regulators run essentially at ambient temp, the power consumption dropped by a couple hundred milliamps to boot. The machines have rock-solid power stability at idle or under operating load, and they run much cooler while using less power overall. 

 

I know if I ever need to replace a 7805 again, or a 7812 for that matter, I will at least try to use a modern switching replacement and see how it goes!  If there is any switching noise on the internal power rails after the swap, that should be able to be addressed by adding one or two small filter caps between the power rails and ground - you might have to play around with the capacitance value but the current fluctuations will be tiny and very fast, so small ceramics would probably be all that’s needed, if anything. 

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Hadn't really thought about those for Percom.... but it is a good idea due to the poor mounting system they used for them.  IIRC there are 3 on a percom.... 12V, 5V, and ?  (I'm not by an open Percom to check... probably a second 5V or 12V... I just can't recall).

 

I think the trickiness in getting any additional filtering caps right as that the switching frequency of the Traco and equivalents change based on load.  I haven't read about these being used in place of the linear regulators and requiring additional filtering....

 

I have considered this for a while for my gear, but the cost (for all of my gear combined) and the fact that my gear works have prevented me from moving forward 🙂 .

 

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there are low cost chinese versions too but beware of the variable output voltage types - they have a small trimpot on. its better to get the fixed output version really

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My only concern would be how long they last and how they fail. The market is full of cheap buck, dc-dc etc. so I also recommend to get the ones with reputable brand name.

Beside the Traco ones I remember there were one more brand that people used here for their 1050s, but I don't remember that name now.

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In my drives, I replaced the regulators years ago.

Saves a lot of energy, thus heat.

And I got the adjustable ones, they work ok.

 

BR/

Guus

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Hello, how safe it is use 16V AC output for 1050 drive ? As far as I know there is voltage boost circuitry which effectively doubles AC input for LM7812 branch which would operate device on the edge of the designed capacity. I don't want to operate drive this way for long time, just until Traco 24050 DC-DC converters are delivered and modify drive for use with 12V DC brick. I wounder should 7812 fail if it just short-circuit to pass 32V to 12V or it just breaks the circuit.

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16VAC when rectified is approx. 22.6VDC, the max input voltage for a 7805 is 25VDC and for the 7812 is 30VDC

so perfectly safe to use, not sure where your 32VDC comes from ?

 

The highest voltage I can see is 25V from the voltage doubler

Edited by TGB1718
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Ok, my bad I do not really understand how voltage doubler circuitry works, I had just impression 16VAC is doubled up to 32VAC then rectified. Anyway thank you for explanation.

My first 1050 behaved strangely on this 16VAC: on power-up it spun just OK but failed to spin next when closing drive (just brief flash of indicator then no motor activity). This was resolved connecting to 9VAC brick - everything worked.

My other drive received today works just completely fine on 16VAC but I am worried whether I am stressing regulators to the max. That was my concern if LM7812 just disconnected 12V branch (thus motor stop) due to overvoltage on the first drive or was it just some failing 7812 approaching the end of life... Unfortunately I didn't try measure 12V was still there, I simply removed all the rectifier, doubler and 7812 circuitry and reworked to standard external 12V DC power supply.

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Hello guys

 

Wouldn't the 1050 get even warmer if you use 16VAC instead of 9VDC?

 

Sincerely

 

Mathy

 

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Yes it would get much hotter as it dumps the extra off. I wouldn't suggest running the drive for long at all.

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15 hours ago, _The Doctor__ said:

Yes it would get much hotter as it dumps the extra off. I wouldn't suggest running the drive for long at all.

Exactly - all that extra voltage has to go somewhere, and since it's obviously not going to higher voltage after being rectified, it's converted to heat.

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7 minutes ago, Peter Kmet said:

I have Traco 2405 DC/DC on the way so due to be replaced 7805 with the unit. 7812 will be removed altogether. According this schematics http://blog.3b2.sk/igi/image.axd?picture=2014%2f1%2fV4PSA1050a.GIF I just needed to test "new" ebay drive to be checked.

v.interesting

can you post a pic when completed?

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11 hours ago, Peter Kmet said:

I have Traco 2405 DC/DC on the way so due to be replaced 7805 with the unit. 7812 will be removed altogether. According this schematics http://blog.3b2.sk/igi/image.axd?picture=2014%2f1%2fV4PSA1050a.GIF I just needed to test "new" ebay drive to be checked.

make super certain to label that drive obnoxiously or change the power jack and plug (labeled nicely) to prevent the inevitable disaster that accidentally occurs when this sort of mod has been done, either at the owners hand or the next person who acquires the drives hands as the habit is always to grab any 1050 supply when mucking about plug it in...

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11 hours ago, _The Doctor__ said:

make super certain to label that drive obnoxiously or change the power jack and plug (labeled nicely) to prevent the inevitable disaster that accidentally occurs when this sort of mod has been done, either at the owners hand or the next person who acquires the drives hands as the habit is always to grab any 1050 supply when mucking about plug it in...

Accomplished! Anyway, I am not planning to sell this drive. Though, these devices are immortal (they died once) - me not. Who knows what they will do with it... 

IMG_20211127_191628.jpg

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22 hours ago, xrbrevin said:

v.interesting

can you post a pic when completed?

I want to keep DC connector center positive while power switch is connected to side (negative). So few traces had to be cut. Overall consumption is now almost 1A when writing and 0.3A in standby. Mr Ziggy would not love this mod - drive feels like switched off [even after extended usage].

IMG_20211127_154141.jpg

IMG_20211127_154336.jpg

IMG_20211127_160132.jpg

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thanks for the pics - nice job!

youre right about Mr Ziggy 🙃

i like the drill option for cutting traces - much neater. am i right in spotting 3 cuts or are there others?

an external 3.5" HDD PSU should suffice for this task

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Check Atari 1050 field service manual. Just 2 cuts were needed (for me, wanting center positive). Third was actually unnecessary, jumper between CR19, CR20 cathodes would do the job (instead of the small white one). Next week I will visit local electronic shop to buy 12V/2A DC switched wall brick.

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On 11/28/2021 at 7:56 AM, _The Doctor__ said:

curios about the SIO cord variant with the red around the strain relief and the shell where the wire comes out.

Shell of SIO is thingiverse model https://www.thingiverse.com/thing:2657213 strain relief was originally rubber piece which I cam not provision anymore so I tried to model own 3D-printed one (yellow).

 

B57DF0F0-A2C8-4BA3-B49A-5A7CA947DA13.jpeg

BB61ACC0-BCAF-4884-A0C6-513FFFA9E05A.jpeg

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looks great, however I didn't see any shield braid on the SIO cable.. is it trimmed that close and neatly or does it not have any?

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7 minutes ago, _The Doctor__ said:

looks great, however I didn't see any shield braid on the SIO cable.. is it trimmed that close and neatly or does it not have any?

Well, there is no shielding at all. It is standard 4 twisted pairs patch cable without shield. 5 wires used only (data in/out, gnd, 5v, command). I am using it for my 1050s. Didn't test it at high-speed, though.

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