WTB Mega ST4 power supply (or repair service)

JonB · Postby **JonB** » Sun Apr 15, 2012 6:57 pm

Hi

Anyone got a working Mega ST power supply for sale?

Alternatively, is there anyone who can repair them?

Also, can the PCB from a 520 ST be used instead? It looks like it will fit on the power supply frame but will it supply enough power?

Thanks

JonB

polbit · Postby **polbit** » Sun Apr 15, 2012 10:22 pm

In US Best Electronics is your best bet, although not sure about prices.

nativ · Postby **nativ** » Sun Apr 15, 2012 10:32 pm

analogic.co.uk still show a repair service.

JonB · Postby **JonB** » Mon Apr 16, 2012 6:56 pm

Can I use the stock ST power supply board? Or will it blow up under the load?

polbit · Postby **polbit** » Mon Apr 16, 2012 9:36 pm

I believe that a stock ST PS is rated at 35W (the later ones at 50W), and Mega ST is rated at 90W. Assuming that continuous load would be much less than that, and the age of the PS, I'd be afraid, very afraid...

Kriegor · Postby **Kriegor** » Tue Apr 17, 2012 1:16 am

polbit wrote:I believe that a stock ST PS is rated at 35W (the later ones at 50W), and Mega ST is rated at 90W. Assuming that continuous load would be much less than that, and the age of the PS, I'd be afraid, very afraid...

My Mega ST2 has got a 50W PSU and i am pretty sure that the Mega ST4 has got the same one. My PSU is non-functional too and i am using another PSU (PC) for it right now. However, it seems like the original PSU has got some dry solder joints, i will try to fix those in a couple of days and see if it helps.

JonB · Postby **JonB** » Tue Apr 17, 2012 6:08 am

Mine likes to blow fuses, rather spectacularly. There are fused components on there as well, it's burned out. So in this instance it's better to replace it I think, as I don't have the time to go swapping out all the defective components.

bid · Postby **bid** » Tue Apr 17, 2012 6:44 pm

This forum thread here shows the various kinds of MEGA ST power supplies. viewtopic.php?t=22635&p=200821

Personally, I think that if the later ST power supplies are 50W. Lets say from an STe. Then surely the MEGA does not use more than this?

After all, all it is powering is one FDD and the mainboard, just like the ST.

If I could find a 50W PSU from an STe, I would personally be tempted to stick it onto the chassis of the MEGA. Maybe I am wrong. But I am just very mean, lol.

I cant imagine that the stock MEGA uses more juice than a normal STe sureley?

BoNuS · Postby **BoNuS** » Tue Apr 17, 2012 7:56 pm

The labels at the underside of my Atari Mega ST2 and Atari Mega ST4 (NT) says:
220-240 volt
50Hz
0.5A
And 120 Watt <--

I can't imagine that 50 Watt PSU will be enough...

I thought a PSU of an SH205 could do it but that only delivers a modest 32 Watt

polbit · Postby **polbit** » Tue Apr 17, 2012 8:40 pm

I took my Mega ST4 apart yesterday and sure enough, it shows 50W. I read in more than one place that a Mega has a 90W, maybe it was meant for Mega STe? Anyway, I stand corrected and why not try the supply for the ST, Mega was meant to power more as it has an extra power connector.

Kriegor · Postby **Kriegor** » Tue Apr 17, 2012 8:50 pm

BoNuS wrote:The labels at the underside of my Atari Mega ST2 and Atari Mega ST4 (NT) says:
220-240 volt
50Hz
0.5A
And 120 Watt <--

I can't imagine that 50 Watt PSU will be enough...

I thought a PSU of an SH205 could do it but that only delivers a modest 32 Watt

The label on the underside of my Mega ST2 also says "120W", the PSU is labeled "50W", the manual says "Max 95W"... I'm not really sure what all that really means though. Apart from the fact that my PSU has gone bad (dry solders or bad caps/other components), it used to drive the Mega ST2 just fine and it's the original PSU.

bid · Postby **bid** » Tue Apr 17, 2012 9:19 pm

Kriegor wrote:The label on the underside of my Mega ST2 also says "120W", the PSU is labeled "50W", the manual says "Max 95W"... I'm not really sure what all that really means though. Apart from the fact that my PSU has gone bad (dry solders or bad caps/other components), it used to drive the Mega ST2 just fine and it's the original PSU.

Hi. Yes, your right. I just checked my MEGA ST4 and it says 120W on the label underneath.

I then checked my 520STe and it also says 120W also. Maybe it would be worth investigating further the PSU situation. It certainly would be great if the STe PSU could be used in the MEGA ST, but I dont know how to confirm it?

Both computers are pretty similar on the face of it. And I'm only guessing that the MEGA may have had a higher wattage PSU for in case an internal card was used on the MEGABUS. But that is only a guess? ... I wonder if someone more knowledgeable on the forum can tell us?

JonB · Postby **JonB** » Fri Apr 20, 2012 4:57 pm

Well, I tried the 520 power supply, transplanting the circuit board into the Mega's power supply chassis (they do fit, the PCB and holes are exactly the same dimensions / positions). It didn't work, just made a high pitched whine and the Mega didn't power up. There are some differences between the boards, the Mega seems to have heavier duty components on it, and I think in this case it would be wise not to risk it. I really don't like the buzzing noise!

Chandler · Postby **Chandler** » Fri Apr 20, 2012 6:54 pm

have you ever had this Mega working?

what happened to the original PSU? did it just stop working 1 day?

a standard ST PSU does work on a Mega without any problems, if you say you had a high pitch wine then it could be a motherboard issue

i have had this on a faulty mega board once before.... a perfectly working PSU and when plugged into this mega it just gave a high pitch wine which then wound down as i switched off power

Kriegor · Postby **Kriegor** » Fri Apr 20, 2012 11:22 pm

JonB wrote:Well, I tried the 520 power supply, transplanting the circuit board into the Mega's power supply chassis (they do fit, the PCB and holes are exactly the same dimensions / positions). It didn't work, just made a high pitched whine and the Mega didn't power up. There are some differences between the boards, the Mega seems to have heavier duty components on it, and I think in this case it would be wise not to risk it. I really don't like the buzzing noise!

Did the monitor go white while the noise was happening during power-up? I had that problem too, solved by simply plugging in the keyboard

The noise in my case was a repeating button-press "noise", which i believed was something more serious until i tried it again. Now it's been running fine for many hours and a lot of reboots - just connect the keyboard when you start it up or you could, just like me, get worried about something that is not to worry about

JonB · Postby **JonB** » Sat Apr 21, 2012 8:34 am

I know the board works as I have tried it with another Mega power supply. There was no life in it when I plugged it in, just a buzz. Monitor stayed black and the power supply fan didn't spin up, although it did when I disconnected the motherboard.

Just to be clear, I actually transplanted the STFM power supply board into the Mega power supply chassis and wired up the fan. That way I could fit it to the Mega properly and safely. Lots of exposed high voltage parts on that board! No joy though. I know the ST supply works as I have used it on another machine. Hey ho, time to pony up for a new board - money sent.

:-)

bid · Postby **bid** » Sat Apr 21, 2012 10:10 pm

Hmm. Could be that it wasnt the power supply after all. But a dead mainboard? ... Hope that you get it fixed. There are a lot of MEGA's on German ebay, and you could put your English roms from the dead machine into the new one.

Sounds like the board is drawing too much current, or alternatively the PSU cant supply enough? Hard to tell.

My STe PSU used to buzz once it got older, and never understood why.

You could try your old MEGA ST power supply on your STfm. Thats a risk tho. As the MEGA PSU would certainly have enough current to power an STfm, and computers only take the current that they want, no more. So you could put a 90W PSU on a standard ST.

Problem with this idea, is that if the PSU is faulty, and delivering the wrong voltage or overvoltage, you might damage your STfm also?

Do we have any electronic engineers on here that actually understand these things, as I am hopeless! :lol:

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