MegaSTE repair

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rubber_jonnie
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Re: MegaSTE repair

Post by rubber_jonnie »

atari030 wrote: Thu Jul 23, 2020 2:50 pm I changed it over to a new TEAC as the SMD was stripped from a PC a few years ago and a tad grotty. I have a decent collection of floppy drives because I knew this day was coming and I grabbed as many from work as I could. ;-) It is all GALled (002) up for 1.44. No AJAX, but the 02-02 hasn't missed a beat with the new drive.

I've still got some problems to iron out, looks like DMA. C398789-001A PLCC type is flakey. I will have to recap the whole shooting match first, I think. Changing one cap can't be a coincidence. I will recap, and then hopefully post will settle down so I can sort a diag cart out.
Diag cart is definitely necessary, and vital for this sort of stuff. I have a decent FDD collection too, as most of my STs are now using Gotek, plus I had some old PC drives around. I have a bench PC that is on the verge of getting a floppy fitted so I can run FloImg on it and retire my Win2K laptop.

Must admit, I've been very lucky, my MSTE never misses a beat and the original floppy and CosmosEx get along just fine.
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...
atari030
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Re: MegaSTE repair

Post by atari030 »

Yeah, that last 1% is significantly harder than the first 50%. :D

My other MegaSTE sits on my desk and gets a decent amount of use. I replaced the battery in it yesterday and marveled at how sparkley clean it was compared to this one. It looks mint. It also is pretty solid. I'm running an external HD floppy, cdrom and HDD of it . Neither of my boxes have internal controllers. The only thing missing on the repair one is the ashtray. I'll try and get one 3d printed.
atari030
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Re: MegaSTE repair

Post by atari030 »

The more I read, the more it looks like a DMA issue, given where I'm at it stands to reason. I'm going to recap the whole board anyway, but I don't think that will cure it. Chris, how is Aussie postage atm? The diag cart looks to be the fastest fix and regardless of the postage pain it looks like the best option.

I'm ordering another desolder/solder station. So now its time to put this aside till the right tools are available. That and plcc DMA chips are rarer than rocking horse do doo I don't want to replace on a whim.
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Re: MegaSTE repair

Post by atari030 »

The rework station arrived, Its like flying after crawling. The joints on this MegaSTE are truly crap, its a lot easier to see how bad they are with the desolder station. But, what was once hours of work is now minutes. Its a bloody little ripper.

I've replaced a few dodgy looking IC's around the DMA and RTC circuits, time to see if it works any better.
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Re: MegaSTE repair

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atari030 wrote: Tue Jul 28, 2020 11:57 am The rework station arrived, Its like flying after crawling. The joints on this MegaSTE are truly crap, its a lot easier to see how bad they are with the desolder station. But, what was once hours of work is now minutes. Its a bloody little ripper.

I've replaced a few dodgy looking IC's around the DMA and RTC circuits, time to see if it works any better.
Once you get a proper desolder station, you'll never look back!
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...
atari030
Posts: 315
Joined: Mon Feb 12, 2018 12:43 pm

Re: MegaSTE repair

Post by atari030 »

I recapped most of the board last night. Up till 1 am.... its like spray painting, chainsawing, etc. You just have to keep going.

Quick question, RJ, is it viable to remove the DMA chip and install a PLCC socket like this?

https://www.jaycar.com.au/44-pin-surfac ... t/p/PI6624

It would be a damn site easier to repair and resolve than soldering in another chip.
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rubber_jonnie
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Re: MegaSTE repair

Post by rubber_jonnie »

atari030 wrote: Wed Jul 29, 2020 12:54 pm I recapped most of the board last night. Up till 1 am.... its like spray painting, chainsawing, etc. You just have to keep going.

Quick question, RJ, is it viable to remove the DMA chip and install a PLCC socket like this?

https://www.jaycar.com.au/44-pin-surfac ... t/p/PI6624

It would be a damn site easier to repair and resolve than soldering in another chip.
I honestly don't know, and I'd have to disassemble my MSTE to look which isn't so easy atm.

I suspect you'd need to look at the pitch of the connections on the DMA chip and figure if the pitch of the socket pins matches that of the DMA chip and PCB, but it's quite a risk. I don't think I'd do it.

Are you sure it's a PLCC package? I haven't spent much time under the hood of mine as it works and haven't looked at the DMA.
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...
atari030
Posts: 315
Joined: Mon Feb 12, 2018 12:43 pm

Re: MegaSTE repair

Post by atari030 »

For a 50p socket, I'll have a look into it. I'm betting my DMA chip is either fried or has a dry joint. I've replaced every IC and cap that relates to DMA. I'll buzz out the lines and I really have to jump on that diag cart. I've been reading up on the TF cards too, I have a surplus of useful Atari and Amiga's so it looks like (another) fun project to get into.
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rubber_jonnie
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Re: MegaSTE repair

Post by rubber_jonnie »

atari030 wrote: Thu Jul 30, 2020 12:52 am For a 50p socket, I'll have a look into it. I'm betting my DMA chip is either fried or has a dry joint. I've replaced every IC and cap that relates to DMA. I'll buzz out the lines and I really have to jump on that diag cart. I've been reading up on the TF cards too, I have a surplus of useful Atari and Amiga's so it looks like (another) fun project to get into.
I just ordered a TF myself, and have another H4 to build, so must get started on that.
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...
atari030
Posts: 315
Joined: Mon Feb 12, 2018 12:43 pm

Re: MegaSTE repair

Post by atari030 »

I should learn not to stuff around with things. She's all recapped, so I decided to drop a socket in for the Ym2149 in case that was causing some of the problems. Back to white screen....... Yes, I broke the golden rule. Do one thing at a time and test as you go.

So I'm ordering the diag cart before I get ahead of myself.
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