That is not the correct way to check for faulty mosfets.
Measure in resistance mode:
between the mosfet gate and source, also between the mosfet drain and source.
If you get anywhere near 0 ohm on either one of those measurements or even both measurements, you have a faulty mosfet.
Which I don't think what you have there.
An older generation GPU card that doesn't show any sign of life at all (no display and fan doesn't spin), is usually because 12V or 3.3V from the PCIe slot is not present.
If 12V and 3.3V from PCIe slot are...
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It doesn't have a PWM chip. The PWM signal is generated by using a mosfet and some transistors logic.
The symptom you described doesn't sound like a faulty PWM, but rather a faulty thermal sensor that will occasionally "sense" the GPU core temperature has crossed over the threshold and the fan has to run at 100% speed, when in fact everything is cool.
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I tried the circuit with my hot air station handle.
Thermocouple reading has 10 degree higher than the temperature I set.
And again you're right about the hysteresis.
Without it, the comparator turns on and off too quick which the LED indicator follows after, and its flickering gives out a negative impression that something is not stable/dodgy when it's actually not. I was able to use the hot air station handle to remove and solder a component without any issue (I had the fan hooked up to a DC PWM circuit to control the airflow)...
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Ok, changed the comparator output resistor to the value you suggested and now it is 230V AC across MT1 terminal and neutral side.
Thanks!!!Last edited by прямо; 04-27-2024, 08:20 PM.
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Here's a short video to show what I meant.
Red DC voltmeter: thermocouple sensor DC mV amplified by 220 times to give a temperature reading in Celcius.
Green DC voltmeter: adjustable temperature threshold (set at 200°C)
LED indicator is on = optocoupler is on = TRIAC is on.
As I mentioned before, measured between TRIAC MT1 terminal and neutral = about 60V AC.
And when the heat that I applied to the thermocouple sensor reached/passed the temperature threshold, LED indicator turns off = optocoupler turns off = TRIAC also...2 Photos
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TRIAC circuit
Anyone is familiar with a TRIAC circuit?
I came across this schematic, and I built it, but I can't seem to figure it out why I'm getting a low AC voltage output at the TRIAC terminals.
With 230V AC hot side at the TRIAC MT2, I measured 60V AC between MT1 and neutral side when the comparator output LED indicator is on, and 20V AC when it is off.
Same result if 230V AC hot side is at MT1, and I measured between MT2 and neutral side.
My heating element doesn't work with 60V AC. It's not even getting hot and the thermocouple amplifier output is a...1 Photo
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I've seen better design from a $2 adapter believe it or not, and yeah, I bought this awhile back for $1. Price don't change for small power adapters like this.
Yup, the core is cool and dandy but the mosfets aren't, they get very hot. I have two of these cards, with a reference blower and with a big fan in the middle. Both has the same core temp, but mosfets are not running hot on the one with the big fan.
Correct. I took the screenshots with the card running on a 1X PCIe slot mining riser.
And btw, a decent DX 9.0 card which is...Last edited by прямо; 04-26-2024, 07:27 PM.
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Ok, so boot into Windows with the integrated graphics so you have a display and see if Windows detects the card.
If the card is detected, then you will see an error code pertaining to the no display symptom (code 43 most likely) which is usually caused by broken connections from VRAM to GPU or from GPU to VRAM.
Run nVidia MATS tool to check which VRAM channel has that problem, and let me know.
...
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My pointless and worthless repair is a 5V 3A switched mode power supply adaptor.
What happened to it was a leaky main cap, and when I plugged, unplugged then quickly plugged back the adaptor, somehow that made the PWM chip blew itself up.
The chip is OB2358AP. It cost about the same as a brand new adaptor, which is around $1.
I replaced the chip and the main leaky cap.
It's been running fine since then.
I also have another pointless and worthless repair.
A GTX 560 SE with missing components and...6 Photos
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https://[url]https://uk.farnell.com/...> [url]https://uk.farnell.com/molex/15020-0387/ffc-fpc-cable-36-core-102mm/dp/3726572[/url]
it's only 10 cm long.
Last edited by прямо; 04-22-2024, 01:22 PM.
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I think you are confused and don't really understand what a short circuit is, and what is actually a very low resistance circuit.
The VCORE has 3 power phases, hence 3 same cascaded HS + LS mosfets and 3 same inductor coils. They should have a similar measurement.
So if one phase is different in measurement compared with the rest, then there is something wrong with it.
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The mosfets are arranged as HIGH SIDE and LOW SIDE.
HIGH SIDE mosfet Drain pin is always connected to 12V
and the Source pin is always connected to the Drain pin of the LOW SIDE mosfet and also to one pin of the inductor coil closer to the mosfet (while the other pin of the inductor coil closer to the GPU core goes directly to the GPU core) if you lifted the coils, the GPU core no longer receives VCORE and will not turn on.
LOW SIDE mosfet Source pin is always connected to GND.
To check if a mosfet is dead:
Measure its...
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Never tested a diode using a resistance mode for my entire history of repairing electronics.
I always use the diode mode, and I replace that has a voltage drop reading out of spec.
You said 3.5 ohm is bad and thus assumed the diode is not normal, but did you even check if the other similar diodes on that faulty board and as well on the working board, have the same resistance?
If 60V 1A Schottky is somewhat not enough, go up to 3A, such as Vishay SS36. It should still fit within the component footprint.
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Refer to the TDA7294 IC datasheet for a Typical Application Circuit schematic.
It should be very similar to your board because the schematic from the IC datasheet works, therefore very rarely a manufacturer using the IC would went as far as to implement a totally different circuit.
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