Looks like I'll be getting a Mega ST4 soon

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exxos
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Re: Looks like I'll be getting a Mega ST4 soon

Post by exxos »

I would say just go on a "mass resoldering" venture and flux the whole thing up and reflow the whole thing starting with the all the main chips and RAM. I had to resolder half of a STFM a few weeks ago which wouldn't boot up but looked like new. Its sadly how these boards seem to be dying, its like the solder gives up the ghost especially each time you move the thing.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: Looks like I'll be getting a Mega ST4 soon

Post by rubber_jonnie »

exxos wrote: Mon Apr 06, 2020 11:32 pm I would say just go on a "mass resoldering" venture and flux the whole thing up and reflow the whole thing starting with the all the main chips and RAM. I had to resolder half of a STFM a few weeks ago which wouldn't boot up but looked like new. Its sadly how these boards seem to be dying, its like the solder gives up the ghost especially each time you move the thing.
@exxos :cry: :cry: :cry:
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
Tomswork
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Re: Looks like I'll be getting a Mega ST4 soon

Post by Tomswork »

I have to do a mega ste has the same problem lots of work for hot air flux and paste. I'm just short of leaded supplies. The corrosion appears to be in side the board dunouts.

Tom
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Re: Looks like I'll be getting a Mega ST4 soon

Post by rubber_jonnie »

@Tomswork the bottom of the board actually seems in better condition than the top of mine with the exception that there are bodge wires and other rework that I've already done. It was extremely grubby when I got it topside and though it's had a damn good clean there is still grime present. The RAM chips all have ground and power, which is great, and given that there is some corruption at the bottom of the screen suggests that perhaps the problem is only related to part of the RAM. Unfortunately the lack of RAM means that though the diag cartridge does try to boot, it doesn't get far enough to do any testing. I will start off by swapping out the 74LS244 chips as that's quick and easy to do, after which I will probably go down the route exxos has suggested, and start reflowing everything in a structured manner. I know this board runs, I've had it running and even stable, it just seems like any physical movement makes it die again, which does play into the possibility that the whole thing has terrible solder joints.

@exxos Just out of curiosity, what is the minimum configuration chip wise that an ST needs to boot? I'm assuming CPU, GLUE, MMU, DMA, MFP, SHIFTER & RAM? I'm theorising that things like the BLITTER, YM, 6850s etc wouldn't prevent it from booting so I can narrow down the areas of investigation. I may test this with the H4, see how little it will actually work with.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: Looks like I'll be getting a Mega ST4 soon

Post by exxos »

You need every chip working.. Maybe not the RTC chip & blitter.. Can't think of anything else.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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Re: Looks like I'll be getting a Mega ST4 soon

Post by rubber_jonnie »

exxos wrote: Tue Apr 07, 2020 11:16 am You need every chip working.. Maybe not the RTC chip & blitter.. Can't think of anything else.
I know it worked without the YM and Blitter, since they weren't present when it arrived, but it still booted. I'm not looking for full functionality, more reducing the areas I focus on reflowing first before going out to do everything on the board :(

I just can't help but think it's either the MMU socket or the LS244s. I know the MMU is good, it works just fine in th H4, so thinking I may have a decent spare socket on another donor board.

Well, I needed to keep busy during lockdown :)
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: Looks like I'll be getting a Mega ST4 soon

Post by exxos »

Ah yep my chip is sound, parallel,floppy stuff. What I do with suspect sockets is lift one corner up on the chip a tiny bit, normally helps. Or place a couple layers of thin card under it to lift it up a bit.

Edit. I guess the 6850 might not be needed either. Or RS232 or -12 v gen circuit.
https://www.exxosforum.co.uk/atari/ All my hardware guides - mods - games - STOS
https://www.exxosforum.co.uk/atari/store2/ - All my hardware mods for sale - Please help support by making a purchase.
viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
Just because a lot of people agree on something, doesn't make it a fact. ~exxos ~
People should find solutions to problems, not find problems with solutions.
Tomswork
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Re: Looks like I'll be getting a Mega ST4 soon

Post by Tomswork »

@rubber_jonnie can you try the piggy back trick with the ls244

Tom
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Re: Looks like I'll be getting a Mega ST4 soon

Post by rubber_jonnie »

Tomswork wrote: Tue Apr 07, 2020 8:05 pm @rubber_jonnie can you try the piggy back trick with the ls244

Tom
@Tomswork In all honesty I don't know if that will work, but the thought had crossed my mind.

It's actually just as easy to desolder with my gun, it takes no time at all and will give me an opportunity to install sockets anyway. Plus once they're out I can test them with my TL866 anyway.

I may try it, will post here anyway with progress.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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Re: Looks like I'll be getting a Mega ST4 soon

Post by rubber_jonnie »

Hi all, so I managed to get some decent diagnostics from the Mega4 thanks to the diag cart and the serial cable.


Here's what I'm seeing:

RAM_Error.jpg
RAM_Error.jpg (156.36 KiB) Viewed 3215 times

If anybody has any experience with interpreting this I'd be very grateful :)

Looking at the data in/out lines on all the RAM chips, out is the same , but 2 chips are showing differences on the data in lines, so it could be those that are dead, but I'd like to try and map the image above into something physical, clearly it is some sort of RAM issue.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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