dead TT motherboard repair attempt

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jookie
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Re: dead TT motherboard repair attempt

Post by jookie »

czietz wrote: Fri Jul 09, 2021 10:50 amI did not test this on my TT, but I find it plausible that a missing SCSI DCU might cause a bus error while TOS is trying to boot from SCSI.
We'll see if that's the case once the DCU arrives from UK to my place... I'll let you know.
czietz
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Re: dead TT motherboard repair attempt

Post by czietz »

In case you have a way to program custom TOS ROMs for your TT, there's another approach you might be interested in trying: EmuTOS (512k ROM version, of course). EmuTOS gives much better error messages than Atari TOS's bombs which might help pinpoint misbehaving hardware. Also, EmuTOS can be custom-built to not use use certain hardware, such as e.g. SCSI.
jookie
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Re: dead TT motherboard repair attempt

Post by jookie »

czietz wrote: Fri Jul 09, 2021 11:30 am In case you have a way to program custom TOS ROMs for your TT, there's another approach you might be interested in trying: EmuTOS (512k ROM version, of course). EmuTOS gives much better error messages than Atari TOS's bombs which might help pinpoint misbehaving hardware. Also, EmuTOS can be custom-built to not use use certain hardware, such as e.g. SCSI.
Thank you for the tip, that sounds great. Unfortunately 27C010 EPROMs are now harder to get and I don't have a working EPROM burner... But I'm thinking of changing the TOS to english as the current EPROMs have 'NETH-FR' on them (Netherlands / French?), which are not languages I speak ;) If I'll get my hands on EPROMs and burner, I'll try the EmuTOS, too.
jookie
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Re: dead TT motherboard repair attempt

Post by jookie »

I've added the MCP100-475 supervisory circuit (4.75V threshold voltage) on the PG (power good) line, removed the pull-up to 5V from that PG line, now the TT starts to boot after power on without manual reset button push.

The DCU (UA01) arrived today, I've soldered it on the motherboard, now the TT boots to desktop without 2 bombs. I didn't test the floppy, ACSI and SCSI yet, so that will follow, but at least it turns on and boots to desktop (when bought from eBay, there was no activity, and 5 chips blocked the machine start). I'm waiting for LMC1992 (U816) to arrive to push it into socket and check if that fixes the DMA sound (which couldn't go through the original soldered LMC1992).

tt_tos.jpg
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exxos
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Re: dead TT motherboard repair attempt

Post by exxos »

jookie wrote: Mon Jul 19, 2021 9:41 am I've added the MCP100-475 supervisory circuit (4.75V threshold voltage) on the PG (power good) line, removed the pull-up to 5V from that PG line, now the TT starts to boot after power on without manual reset button push.
Sounds like the reset circuit needs a recap. Same problem happens on the STE etc. I even suggest using higher values to allow the PSU to power up fully before reset happens.
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viewtopic.php?f=17&t=1585 Have you done the Mandatory Fixes ?
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jookie
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Re: dead TT motherboard repair attempt

Post by jookie »

exxos wrote: Mon Jul 19, 2021 9:46 am Sounds like the reset circuit needs a recap. Same problem happens on the STE etc. I even suggest using higher values to allow the PSU to power up fully before reset happens.
Thank you for the info, I will look into that, too.
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rubber_jonnie
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Re: dead TT motherboard repair attempt

Post by rubber_jonnie »

jookie wrote: Mon Jul 19, 2021 9:41 am I've added the MCP100-475 supervisory circuit (4.75V threshold voltage) on the PG (power good) line, removed the pull-up to 5V from that PG line, now the TT starts to boot after power on without manual reset button push.

The DCU (UA01) arrived today, I've soldered it on the motherboard, now the TT boots to desktop without 2 bombs. I didn't test the floppy, ACSI and SCSI yet, so that will follow, but at least it turns on and boots to desktop (when bought from eBay, there was no activity, and 5 chips blocked the machine start). I'm waiting for LMC1992 (U816) to arrive to push it into socket and check if that fixes the DMA sound (which couldn't go through the original soldered LMC1992).


tt_tos.jpg
Excellent work sir.
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...
jookie
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Re: dead TT motherboard repair attempt

Post by jookie »

rubber_jonnie wrote: Mon Jul 19, 2021 11:27 am Excellent work sir.
Thank you :)

I've also just managed to complete a side quest - extending the 2 MB ST RAM on a card to 8 MB ST RAM...

Removing 2 MB chips from the RAM card - 1 hour with a soldering iron

desolder0.jpg
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Removing 8 MB chips from SIMM from eBay - 5 minutes with a paint removing hot air pistol

desolder1.png
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Soldering 8 MB chips to RAM card - 1 hour 40 minutes

solder.png
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TT memory test on boot (the RAM was also tested via RAM test on diagnostic cartridge).

boot.png
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stephen_usher
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Re: dead TT motherboard repair attempt

Post by stephen_usher »

:dualthumbup:
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
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Icky
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Re: dead TT motherboard repair attempt

Post by Icky »

That's a nicer solution for the SMT boards. The through hole is a pain to desolder and clean up but Lyxman's ram board add-on works well.

Great work :)
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