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1541 Replacement PSU

robert_sissco

robert_sissco

Experienced Member
Joined
Oct 12, 2021
Messages
342
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Midwest U.S.A.
I have a 1541 with a dying transformer (It hums like I do when I am forced to sing) and I am wanting to replace the power supply with a more modern one. I have seen many modern switching power supplies online, but none that have both the 5v and 12v out. Does anyone have a link to one that will work? I have links on how to set it up, I just need to find one that works for both voltages.
 
Meanwell make a lot of dual 5V 12v psu's, You will have to select one with the required power and physical size to go in the space available.

All the major suppliers normally carry these supplies.

RD-35-MEAN WELL Switching Power Supply Manufacturer

MEAN WELL is one of the world's few standard power supply mainly professional manufacturers, covering 0.5 to 25,600W products are widely used in industrial control, medical and other fields, in line with international safety certification, short delivery of spot inventory.
www.meanwell.com

Check out RD50, RD65, RD85 models etc for higher powers.

I used the RD65A in some disk drive units:


Transformers are normally not in a dying mode, usually they are ok, or have failed. The humming can just be some loose laminations in the stack and it can be cured often by additional varnishing.
 
Hugo Holden said:
Meanwell make a lot of dual 5V 12v psu's, You will have to select one with the required power and physical size to go in the space available.

All the major suppliers normally carry these supplies.

RD-35-MEAN WELL Switching Power Supply Manufacturer

MEAN WELL is one of the world's few standard power supply mainly professional manufacturers, covering 0.5 to 25,600W products are widely used in industrial control, medical and other fields, in line with international safety certification, short delivery of spot inventory.
www.meanwell.com

Check out RD50, RD65, RD85 models etc for higher powers.

I used the RD65A in some disk drive units:

Click to expand...
I had been checking out Meanwell, but I only ever found 5v OR 12v, not both when searching on sites, thus my question
 
Hugo Holden said:
Yes their RS model number prefix means "single supply", but the RD means "dual supply".

Not unlike Star Wars, when it turned out that Darth Vader was Luke's Father, and everybody seemed surprised, yet "Vader" means Father.
Click to expand...
Didn't know about the part coding they did, but I did know Vader meant Father in Dutch.

Either way, info gained, so....

knowing-is-half-the-battle.jpg
 
If there are as many dead 1541s as so many on here claim (because of failed read/write heads; couldnt you find a replacement transformer from one of these? Another member in your vicinity could send you one.
 
VERAULT said:
If there are as many dead 1541s as so many on here claim (because of failed read/write heads; couldnt you find a replacement transformer from one of these? Another member in your vicinity could send you one.
Click to expand...
I have four working ones, and this was a 5th I bought off of eBay that was listed as Not Working, No Power since I wanted the case as there was no damage to it and a possible cheap parts board. It powered up for me first try, though I did need to replace thee DOS ROM to get it to work. Since I need to go through the effort of removing the old transformer, I would like to do a bit of future proofing on this one, plus looking at it the info @Hugo Holden sent me the PSU will be less than $20 from most suppliers from a decent manufacturer. I have a spare sled already for it, so I just need to add it there, then test just my moving the power connector to the drive, and if it works, move the drive from the sled with the dying transformer to the new one and then put that into the case.
 
@Hugo Holden Quick question if I may pick your brain. The document you liked showed the RD-35A, have you used this, or would you recommend I go to the RD-66? I simply ask due to the Amperage difference
 
robert_sissco said:
@Hugo Holden Quick question if I may pick your brain. The document you liked showed the RD-35A, have you used this, or would you recommend I go to the RD-66? I simply ask due to the Amperage difference
Click to expand...
I have only used the RD-65 and RS-15, I would think that the RD -65 would be more than adequate. You need to check your power requirements, you might be able to get away with a smaller unit in the RD series power supplies, like the RD-35. You need to determine the power rating you require from the product of volts x amps, for the 12 & 5V supplies for the 1541...have you measured the 5V and 12V current drain ?
 
The thing is that the peak current draw on the 12V rail is >1 A while starting up the motor and around 700 mA - 1 A when running.

The 5 V rail will draw about 500 mA without any addons.
I've used a cheapo aliexpress 3€ dual supply rated for 1 A per rail and it hiccuped half of the time on power up. If you get a decent one rated 1.5-2 A on the 12 V rail you should be fine.
 
powerlot said:
The thing is that the peak current draw on the 12V rail is >1 A while starting up the motor and around 700 mA - 1 A when running.

The 5 V rail will draw about 500 mA without any addons.
I've used a cheapo aliexpress 3€ dual supply rated for 1 A per rail and it hiccuped half of the time on power up. If you get a decent one rated 1.5-2 A on the 12 V rail you should be fine.
Click to expand...
Thank you, that does help greatly.
 
robert_sissco said:
Again, just wanting to do a bit of future proofing on this by giving it a power supply that doesn't double as an oven
Click to expand...

I'm not convinced that putting in a modern SMPS supply would future proof it. Most of the electrolytic capacitors used in SMPS's have fairly high ripple currents and sometimes you can only get 1000 to 3000 Hrs out of them, depending on the initial quality & ratings.

I think it is better to keep the original analog supply and improve the cooling with better ventilation by adding some fans. I "future proofed" my SFD-1001 this way, there is thread about it here:

 
Hugo Holden said:
I'm not convinced that putting in a modern SMPS supply would future proof it. Most of the electrolytic capacitors used in SMPS's have fairly high ripple currents and sometimes you can only get 1000 to 3000 Hrs out of them, depending on the initial quality & ratings.

I think it is better to keep the original analog supply and improve the cooling with better ventilation by adding some fans. I "future proofed" my SFD-1001 this way, there is thread about it here:

Click to expand...
My other concern is this. The eBay seller listed as No Power and noted in the description that he did test it by plugging it in and turning it on and none of the LED's turned on and made no noise. I opened the case when I first got it and all wires were connected (I thought maybe the power connection from the PSU to the board was disconnected) but as all were good I tested it myself to see what happened, and it turned up and spun up right away and kept spinning (was a bad DOS ROM that I replaced to fix that issue) but the humming continued.

I am not sure if the USPS did a bit of unintentional percussive maintenance for me in shipping, but it worked when I got it home.

I have added fans and heatsinks to my other 1541s and to this one (at least the heatsinks so far), but this unit was reported as being dead by one user and is humming a bad song to me, so even if I epoxy coat is, I still do not trust it to keep working. Even if a Meanwell PSU gets me 1000 hours only, I do not trust this particular transformer to work even that long. Yes, it was a $10 parts machine, but if I can save it and get it working fully with a new power supply for $20 more, I am wanting to do so. If it was completely dead or the board damaged then I wouldn't care.
 
robert_sissco said:
, I do not trust this particular transformer to work even that long.
Click to expand...

Transformers, generally are extremely reliable. I have many transformers in apparatus that were made from the 1920's , they still work today.

Here is an example of signal transformers that were made in 1927 & still work:

www.worldphaco.com/uploads/UX-171-A_Class_AB1_push_pull_amplifier..pdf

Generally you can trust transformers unless they have been badly overheated degrading the enamel insulation on the copper wire.

I submit that your humming transformer is perfectly fine, and if you dipped the transformer in varnish, the humming would go away, because it just represents a free lamination vibrating in air. It is not a marker that your transformer is defective.
 
I'll second that. I have another hobby, vintage electric trains, and we routinely use transformers from the 1950s. Modernizing them with newer circuit breakers is common, but the transformer core itself is still the same 70-year-old part. And yes, it's normal for a transformer to hum, it's a side effect of the AC current flowing through it.

The voltage regulators produce more heat than the transformer, so you can replace the regulators with modern switching types to get a hybrid approach to cool the drive. Also replacing the 6522 VIAs with more efficient 65C22 VIAs cuts heat generation quite a bit. Swapping in a 65C02 CPU can also help but can cause compatibility issues.
 
robert_sissco said:
OK, so if I am to keep the transformer, what do I need to cover in epoxy? Just the copper wire?
Click to expand...
Probably you don't need to do anything to it. If the humming is annoying you, you might be able to identify where it is coming from and put some resin over that part. If you can't see it, you can remove the transformer and submerge it in a tin of varnish (marine spar varnish works well, its similar to transformer varnish). This is more or less what is done at he factory, except they provide a vacuum which helps the air leave the crevices between the winding wires and laminations and the varnish replaces the air. You could leave it in there for some hours to help it soak in to the small spaces. Then remove it and let it drip dry. Leave it then for a few days so the varnish sets and is not tacky to handle. That should quieten it down.
 
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