Electronics > Repair
DL1540 Repair
cattlot:
--- Quote from: Swake on December 29, 2024, 09:00:05 pm ---That 'digital' signal pulling upwards over time indeed is bizarre. I have never seen this before.
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it really is strange, could there be like a capacitor charging on the pin or something? I dont really think its a problem tho and just more a quirk of the system because it only acts like that when its idle and the mpu just doesnt control it? I probably am wrong tho
--- Quote from: Swake on December 29, 2024, 09:00:05 pm ---Assuming that with 'static' you mean a screen full of noise pixels. Static on the screen of an old TV with a tuner meant 'no signal'. Would you be able to inject some other video signal in the CRT to exclude that part? Of course you'll need to find were to inject it first.
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I dont really have a way to put anything on screen as i dont have any tv equipment, but i know where to put in the signal as one of the pins directly connect to a signal amplifier . What i mean by static is like when power is turned off the crt lights up full screen and as the caps drain I can see the indvidual traces of the crt die down, kind of like how old tvs act when turned off (best way i can describe it), Ive seen other DL1540's act the same way on videos online.
--- Quote from: Swake on December 29, 2024, 09:00:05 pm ---Would think that it might somehow be found back in the power supply current consumption.
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wdym?
What i found out is that the bus does actually works and does some form of initalisation on the components on the CPU board, because if a pin was held high by me shorting a data pin, the boot chime didn't happen so i think that the CPU board's main components do work.
in the interconnect of the CPU board and AQC board the bus does connect to it but through a HC245 bus tranciver and on the AQC side of the bus it showed really weird behavior, maybe there is a problem with it? but i want to do a bit more reaserch before i do anything
Ive also got a seperate question, on the analog board the +5v and -5v have low resistances (49 \$\Omega\$) and (71 \$\Omega\$), could this be a sign of a faulty chip? or is it a red herring, as ive mentioned prevously the components on that board get very hot so like idk
Swake:
--- Quote ---because if a pin was held high by me shorting a data pin, the boot chime didn't happen so i think that the CPU board's main components do work.
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Best tip of the day. This is such a simple test that it is borderline genius.
if the CPU goes idle that can mean that
- it hangs for some reason, like the firmware is corrupt.
- it does not receive any 'boot data' and just stops till the next reset.
- some protection kicks in. (like it knows somehow that the video card is broken)
- it is not being reset continuously by the reset chip, else you would see the startup sequence over and over again.
--- Quote ---Ive also got a seperate question, on the analog board the +5v and -5v have low resistances (49 \$\Omega\$) and (71 \$\Omega\$)
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That gives about 100 mA on the positive side and 70 mA on the negative side. 0.85 Watt, not really cooking power if you ask me. If you had something shorted like a dead tantalium cap it would be a different story.
--- Quote ---could this be a sign of a faulty chip? or is it a red herring, as ive mentioned previously the components on that board get very hot so like id
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Hot is relative, if steam raises up when you put a wet finger on it, then yes it is too hot ;D There is likely another source of power on top of the + & - 5 V as less than a watt really is not all that much.
--- Quote ---wdym?
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That mini staircase effect must have a reason. I've only seen a somewhat similar waveform probing DDR3 memory, but that is 1 or 2 nS timing not 500 nS, and likely had an entirely difference cause. I'd like to understand where this is coming from. It is a very long shot that you might be able to measure the current delivered by the power supply and find back that specific staircase in the current trace.
Remarkable is that when the signal comes down it jumps below 0 V, that is extra weird, as if there was a negative voltage available. An opamp could play that game, only this is TTL stuff. Is some near dead component feeding the -5V somehow back into digital (data) lines? Now that I re-think it, this might be a probing issue, but 2 V negative is a lot.
Somehow it makes me think of a composite video signal. But that should not make any sense.
Could you disconnect the power supplies from the rest and connect it to an electronic load, or some resistors as load. The idea is to measure ripple with a constant load and find out if the power supply is not having some lower than normal limit somewhere.
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