STE with no signs of life

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LaceySnr
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STE with no signs of life

Postby LaceySnr » Sat Jan 20, 2018 12:54 pm

Ok, so recently my STE had been missing the green channel completely. I thought this was my DIY RGB cable, so I ripped it apart and re-soldered it (I actually meant to test it first, but it was such a poor job the ripping apart happened as I disconnected it... those 13 pin DIN plugs are tricky to solder!). I tested it after resoldering it and continuity mode of the multi-meter was all good so I hooked it up and powered on, alas, still no green.

Figuring there may be a bad solder joint on the connector on the board I took the machine apart but nothing was obviously wrong. I powered it up naked, with just the display attached, and sure enough, I got a TOS desktop in full colour. Ok, let's put it back together. I put on the annoying as hell back plate and put it on the base of the RF shielding, then figured I'd test again before going any further and that's when it seemed dead. Took the crappy panel off again, put it back down naked, and still blank. There's an occasional flash on the screen toggling the power, but that's it. I can't see anything obviously bad on the motherboard, and have given everything in a socket a gentle prod or two to no avail. The CPU felt pretty hot after a short while, but I'm not sure how hot they get in use.

Where's the best place to start diagnosing this? All the caps look good, and the power supply is putting out 5.1 on the two 5v lines and 11.8 on the 12, all holding steady.

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LaceySnr
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Re: STE with no signs of life

Postby LaceySnr » Sat Jan 20, 2018 1:01 pm

Ok, feeling stupid now. I disconnected my monitor lead, and the thing probably boots (at least the floppy drive kicks in and does as it should). I recall having this issue before with my cable the first time before giving it a good jiggle. Anyone know what the actual cause is? I assume it's either a bad ground, or something grounded that shouldn't be? Would the wrong resistance on the sync and/or colour channels potentially cause it?

czietz
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Re: STE with no signs of life

Postby czietz » Sat Jan 20, 2018 1:44 pm

The STE has the ability to switch to an external clock input altogether, iirc by grounding pin 3 on the monitor connector. Maybe check for shorts on the resoldered connectors.

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Re: STE with no signs of life

Postby Atari030 » Sat Jan 20, 2018 10:11 pm

Do you need another monitor to check with?

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Re: STE with no signs of life

Postby tzok » Sat Jan 20, 2018 11:43 pm

Exactly - the monitor pinouts are showing the monitor plug from the pins side, so the pin numbering is mirrored... once I've connected Composite Video to pin 3 instead of 2 and this made my STE "dead". In reality it doesn't hurt it, but prevents from booting. Pin 3 is above the red channel it must not be connected anywhere.

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LaceySnr
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Re: STE with no signs of life

Postby LaceySnr » Sun Jan 21, 2018 2:57 am

Yeah I've gotten used to staring at those damned diagrams having made up mono cable and now the RGB one twice, but I'd not realised about pin 3. I checked it and couldn't find anything obvious, but snipped it off the connector to be on the safe side since I'm not going to use it anyway. I still had troubles when the plug shielding was attached, but realised I hadn't grounded that. Adding a ground wire to that (to pin 13) seemed to help. Now she's back together, though minus the farking annoying flimsy rear panel cover (worst part on these machines) and with only one screw left over :P

Thanks for the input guys, appreciated it. Also thanks for the monitor offer!


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