So you have another good PSU that works in another machine, which means you have a good power source that does not work, and by the behaviour you stated, it seems to be going through repeated on/off cycles.
You may want to have a look at the /RESET line on the CPU, see what that is doing, it might indicate a problem with the reset circuit tripping repeatedly.
Next I'd suggest looking at the MSTE schematic and working in from the power connector, looking at the power good signal and where that is derived from, and if that is also cycling, see if you can determine what's causing that.
What might be an advantage is if you have an ossciloscope, you may be able to catch the timing of events and see if the power good or reset trips before the 5v line drops.
MegaSTE flashing keyboard light only
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Re: MegaSTE flashing keyboard light only
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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...
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...
Re: MegaSTE flashing keyboard light only
thanks for the reply.
Well I do have a scope. Have not really had the time to learn more than the basic measurements.
I will see what I can figure out from the reset. I think I am more on the idea of some kind of short.. Cap 227 comes out of the power connector 5v. It looks good. I am going to clean up my area today and find my CAPacitor tester. IT is 470UF .. a significant charge.. all the others are none polorized .1uf caps.. dont think they could effect this.. none ground out.
James
Well I do have a scope. Have not really had the time to learn more than the basic measurements.
I will see what I can figure out from the reset. I think I am more on the idea of some kind of short.. Cap 227 comes out of the power connector 5v. It looks good. I am going to clean up my area today and find my CAPacitor tester. IT is 470UF .. a significant charge.. all the others are none polorized .1uf caps.. dont think they could effect this.. none ground out.
James
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Re: MegaSTE flashing keyboard light only
Usually a short doesn't cause power flickering on and off. A short usually ends up blowing a fuse if you're lucky. And since the psu seems good, it doesn't sound like that. I'm thinking something in the reset circuit also.
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Re: MegaSTE flashing keyboard light only
Also a thought....someone correct me if I'm wrong. I know you tested the psu with a hard drive, but I think a psu can still fail under a higher load such as when you are powering the whole system even though it seemed fine with just a hdd only. Do you have another known good psu to try in the megaste?
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Re: MegaSTE flashing keyboard light only
You can use any old AT-PC PSU too ...
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Re: MegaSTE flashing keyboard light only
Wonder if a flaky voltage regulator could cause these symptoms?
Re: MegaSTE flashing keyboard light only
He says in the first post he's tried a known good PSU..TheNameOfTheGame wrote: ↑Thu Feb 04, 2021 6:48 pm Do you have another known good psu to try in the megaste?
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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.
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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.
Re: MegaSTE flashing keyboard light only
Bikerbob wrote: ↑Mon Feb 01, 2021 4:23 pm So is it Powergood that I am not getting right here? and thats why the PSU is not starting up? I get its a protection, but not sure what I am supposed to be checking here. I notice the reset is not in this part of the circuit, and I assume that could still be one of the issues.
As others mention.. you need to check POWER GOOD line and RESET line..
RESET should be 0V when you turn on the ST (or holding down the reset button) it should go to 5V shortly afterwards.. you can check on a meter...
(can't for the life of my find the reset circuit in the MSTE diagram!)
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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.
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.
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Re: MegaSTE flashing keyboard light only
Ah, thanks, I missed that.exxos wrote: ↑Thu Feb 04, 2021 7:09 pmHe says in the first post he's tried a known good PSU..TheNameOfTheGame wrote: ↑Thu Feb 04, 2021 6:48 pm Do you have another known good psu to try in the megaste?