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TT won't boot; "flashing" white screen pink square

Problems with your machine in general.
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Nethak
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Joined: Tue Oct 11, 2022 11:40 pm

TT won't boot; "flashing" white screen pink square

Post by Nethak »

IMG-2138.jpg
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Upon powering on the machine, I get a white screen with a pink box. The box stays consistent, but there's a "flashing" that appears to be an overlay that washes out the pink box every two seconds. I saved a video of it to YouTube here. If I insert my TT030 diagnostic cartridge, the screen appears immediately upon power-on. If I remove the cartridge, the screen appears after about 5-10 seconds. Hitting/holding reset results in the screen eventually coming back on once released.

I don't have advanced tools for troubleshooting, so I took the "parts cannon" approach of replacing the PSU and every socketed chip from another known good and working TT that I have in my collection. To reiterate, I have swapped out the memory, TOS, and all socketed and PLCC chips, but nothing changes. The good news, I guess, is that I have other TTs for parts swapping, but all I've really learned is that the problem lies in something that I was not able to swap out -- some component or logic still soldered to the board.

As a next step, I will read the TT field service manual and try figure out how to check for clock signals and reset lines - treating it as "dead". I just thought I'd ask the group if they've ever seen anything like this before to point me in a direction.

Thank you.
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stephen_usher
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Re: TT won't boot; "flashing" white screen pink square

Post by stephen_usher »

I take it that you hooked up a terminal on the serial port to see if anything comes out when you put the diag cart on the machine?

Oh, and have you checked the voltages coming from the PSU?
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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mikro
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Re: TT won't boot; "flashing" white screen pink square

Post by mikro »

You wont find anything specific in the service manual except what @stephen_usher told you: diagnostic cartridge here is key. That magenta doesn't come from software, so it looks like a hardware fault (TTVIDEO, MCU etc). However there's still chance that the diagnostic cartridge will boot and show something meaningful on terminal.

Also, perhaps you should have mentioned history of this TT: has it ever worked? Is it a purchase "as is" from an unknown seller ?
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