Mega ST PSU - can i use this replacement part?

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MRAtari
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Mega ST PSU - can i use this replacement part?

Postby MRAtari » Wed Jun 08, 2011 4:41 pm

repairing a Mitsumi Mega ST PSU which has the usual black fuse, anyway Q1 / Q2 and PC 101 are dead (all else is good)

i have a Q2 and PC 101 but the Q1 which is a 2SC3457 3 legged transistor is a bit rarer or silly money for just 1

what i'd like to know is can i use a Philips BU508A (as used in the original Atari psu) in place of the 2SC3459?

they are very similar and just need to know if the BU508A is upto the job

i've attached the spec sheets

:)
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Nikolas
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Re: Mega ST PSU - can i use this replacement part?

Postby Nikolas » Wed Jun 08, 2011 5:22 pm

Hello, remember not to have atari power cable that comes out from psu plug into mainboard when your powering up your psu for first time.
Then As regulas power volt need to be +5v +12v and check capacitarors, if they are ok. And run your psu atleast 10 minutes with no load (free run).

Anything more topic related i cant tell.
If you guys expirience hardware problems.
1. Always remove chips if possible before soldering.
2. Resolder your hardware, check cables too.
3. If problem continue THEN must be faulty software.

I got 2 Atari ST
Main is stfm, with blitter, with 4 meg of ram, with 16mhz cpu + s-video and audio input to videobox, vdi out
P.S.
My english may not be correct

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Re: Mega ST PSU - can i use this replacement part?

Postby Hippy Dave » Wed Jun 08, 2011 9:00 pm

My opinion:

Mitsumi would use a 2SC3459 because this would be a
conveniently sourced Japanese transistor.
Europeans would use the BU508A for the same reason.
Americans would use a 2Nxxxx.

One spec that can matter here is Vceo = 700V for the
BU508A; 800V for the 2SC3459. However, 700V is
sufficient because the transistor will normally see less
than 360V when it is being turned on. When the
transistor is turned off the voltage may exceed 800V,
but the Vces = 1500V is in play at this time.
(Vcbo = 1100V for 2SC3459)
______________
Last edited by Hippy Dave on Thu Jun 09, 2011 5:46 am, edited 1 time in total.

MRAtari
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Re: Mega ST PSU - can i use this replacement part?

Postby MRAtari » Wed Jun 08, 2011 9:28 pm

thanks hippy dave

yes i noticed the 700v / 800v too but concluded that neither would have to deal with 700v for this application

i will try with a Bu508A and see........

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Nikolas
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Re: Mega ST PSU - can i use this replacement part?

Postby Nikolas » Thu Jun 09, 2011 11:31 am

Hier input voltage better it is. i think minimum must be 600 volts..
If you guys expirience hardware problems.
1. Always remove chips if possible before soldering.
2. Resolder your hardware, check cables too.
3. If problem continue THEN must be faulty software.

I got 2 Atari ST
Main is stfm, with blitter, with 4 meg of ram, with 16mhz cpu + s-video and audio input to videobox, vdi out
P.S.
My english may not be correct

MRAtari
Captain Atari
Captain Atari
Posts: 494
Joined: Thu Apr 05, 2007 5:03 pm

Re: Mega ST PSU - can i use this replacement part?

Postby MRAtari » Thu Jun 23, 2011 6:33 pm

well tested it and......nothing

no output at all from PSU but no blown fuses either!

and the heatsink on the primary side starts getting warm when switched on as normal

maybe it is ok and the psu has other issues, i dunno as i never did have it working

checked all caps and diodes all ok, it's really clean too like it's hardly been used

anything else i should be looking at?

:)


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