Mitsumi 68-4242a

Repairs & upgrades.
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Bikerbob
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Mitsumi 68-4242a

Post by Bikerbob » Sat Nov 30, 2019 3:04 pm

These are the power supplies I have in my MegaST computers (3 of 4) I have never seen these listed or tested.

The large Cap on this one is a 220ohm 200v. I can find a Panasonic 105deg good size FR series (digikey does not list esr) at this rating - very common.

Do I - or should I up the value on this one for a recap? Some of the smaller ones were a little dodgy.. this one looks great. The PSU was dead though, no fuse blown - but it had been removed not working. I get values or continuity through all tested caps and resistors, I have not tested with power or load yet.

James

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DoG
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Re: Mitsumi 68-4242a

Post by DoG » Sat Nov 30, 2019 3:41 pm

What model number does it say on the sticker underneath the metal stand the board screws into?

You should be able to find PSU schematics on https://docs.dev-docs.org/ after that.

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exxos
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Re: Mitsumi 68-4242a

Post by exxos » Sun Dec 01, 2019 12:12 am

Kinda looks like some revision of a SR98 to me, but not seen that exact version before.. The SR151 is totally different.

https://www.exxoshost.co.uk/atari/last/psu/index.htm

Looks like the SR98 was 68-4237?

Looks like they must have moved to a smaller opto.. then had to move the trimmer the other side of the heatsink to keep it away from the HV side. So maybe they couldn't get that older opto anymore and had to change to a alternative part towards the end of the production runs.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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Cosmic Puppet
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Re: Mitsumi 68-4242a

Post by Cosmic Puppet » Sun Dec 01, 2019 12:56 am

SNAP! I have the exact power supply on my STFM.
Atari 520 STFM (C070523-001 REV.D1) 4MB, TOS 1.04 (now using EmuTos), Ultrasatan with 14x 511MB gemdos drives, Original Floppy Drive.

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Re: Mitsumi 68-4242a

Post by exxos » Sun Dec 01, 2019 1:18 am

Cosmic Puppet wrote:
Sun Dec 01, 2019 12:56 am
SNAP! I have the exact power supply on my STFM.
What is the model number on the bottom ?
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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Bikerbob
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Re: Mitsumi 68-4242a

Post by Bikerbob » Sun Dec 01, 2019 1:54 am

DoG wrote:
Sat Nov 30, 2019 3:41 pm
What model number does it say on the sticker underneath the metal stand the board screws into?

You should be able to find PSU schematics on https://docs.dev-docs.org/ after that.
Nothing not a sticker anything on any of the trays.


So what about the question of upping the value of the hivolt cap.. 220ohm 200v?? should I up that?

I have a megaST where the PO replaced it with a meanwell.. I am going to keep that in.. as its 50w and I am putting in a PAK68/3 and they suggest getting up to 50w to have all the EXTRAS. :)


James

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rubber_jonnie
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Re: Mitsumi 68-4242a

Post by rubber_jonnie » Sun Dec 01, 2019 9:36 am

I'd be tempted to go fo a Meanwell, at the price they are a steal and if you're going to add the PAK then you can be pretty sure it'll be more than up to the job.
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Cosmic Puppet
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Re: Mitsumi 68-4242a

Post by Cosmic Puppet » Sun Dec 01, 2019 1:01 pm

exxos wrote:
Sun Dec 01, 2019 1:18 am
Cosmic Puppet wrote:
Sun Dec 01, 2019 12:56 am
SNAP! I have the exact power supply on my STFM.
What is the model number on the bottom ?
It's 68-4242A
Atari 520 STFM (C070523-001 REV.D1) 4MB, TOS 1.04 (now using EmuTos), Ultrasatan with 14x 511MB gemdos drives, Original Floppy Drive.

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exxos
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Re: Mitsumi 68-4242a

Post by exxos » Sun Dec 01, 2019 1:04 pm

Cosmic Puppet wrote:
Sun Dec 01, 2019 1:01 pm
It's 68-4242A
Odd theres no sticker on bottom with a proper part number though, I'm just going to call is "SR98 REV1" and there, problem solved :)
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.

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