tehsiggi wrote on Today, 05:07:

The write-up instructions don't look too bad. I don't know of course the menus of your rigol, but you'll get around them I am su […]
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The write-up instructions don't look too bad. I don't know of course the menus of your rigol, but you'll get around them I am sure of that.

I'll see today if I can find any card in my stash that uses a similar schematic, so I can see what normal operation would look like on pins for your reference.
Fingers crossed.

The similar rail resistance gives me hope as well!

Well I configured the Rigol like so (I think)...

But when I measure the SS pin, I don't get any sort of signal so I'm probably not doing something right on the Rigol.

After going through all the menu options and configuring settings, I feel the oscilloscope is like a hobby in itself.

I guess I'm hitting a dead end with my technical abilities here 🤣. A bit disappointed. I have ordered some replacement ISL6525's incase the chip itself is faulty.

Just for verification, connect the probe to the 5V of your PSU. You should see a nice flat line around the 5V mark on your scope.

I don't expect this to be a measurement issue to be honest. Perhaps we're seeing already what's bad.

shevalier wrote on Today, 07:14:

According to the ISL6525 block diagram, its oscillator should start immediately.
Check for a sawtooth voltage on pin 1.

I checked the ISL6522 (which is basically the cousin). The RT principle is the same as for both (same formula, same functional description by either strapping it with a resistor to +12V or GND).

I measured (3!) working ISL6522 on a Radeon 9500 Pro, which all have a flat voltage on RT. I don't think it's directly part of the RC oscillating circuit, since it can also be omitted. So I wouldn't bet on that as a verification to see if the ISL runs. The noise I have on the flat line is the same as if I would just connect the probe to ground. Noise, to be expected.

Just to verify: Yes, the ISL is running at around 290kHz and my measurement setup works, here is the PHASE pin of one:

And I also measured that just with the ground wire going to the AGP slot bracket, no sweat.
Don't overengineer what you're trying to do. We should see a voltage going to around 4V on SS. Either flat (working fine) or ramping (if current limit). That's not hard to measure and works easily with even the jankiest setup. Is it the best way to measure? Of course not. Is it sufficient? Yes. Don't sweat it.

tehsiggi wrote on Today, 09:59:

which all have a flat voltage on RT. I don't think it's directly part of the RC oscillating circuit, since it can also be omitted.

This depends on the controller's internal circuitry.
When using a current mirror, a straight line will be displayed.
Sometimes artifacts from sawtooth voltage of several mV are visible.

If there is nothing holding ISL from starting (some external power sequencing circuit), then it looks like it has totally failed.

shevalier wrote on Today, 10:45:

This depends on the controller's internal circuitry. When using a current mirror, a straight line will be displayed. Sometimes a […]
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tehsiggi wrote on Today, 09:59:

which all have a flat voltage on RT. I don't think it's directly part of the RC oscillating circuit, since it can also be omitted.

This depends on the controller's internal circuitry.
When using a current mirror, a straight line will be displayed.
Sometimes artifacts from sawtooth voltage of several mV are visible.

If there is nothing holding ISL from starting (some external power sequencing circuit), then it looks like it has totally failed.

The interesting part about the ISL6525 is that it does not have the EN pin, like the ISL6522. There is a potential connection between the AGP PG signal and OCSET, however R1305 (0Ohms) is not populated, so that "over-current trigger" to inhibit operation is not in place.

So we know that the 12V are present to power the ISL (measured through R1262, having 12V on both ends). We don't see any activity on SS, which is odd (either solid 4V or ramping is to be expected (current limit)). So perhaps that ISL just gave up? If the caps are blind, at least some activity should be there.

Just for some sanity checks Zuldan, could you measure resistance of:

• GL1 (Gate, Pin 4 of Q905) against ground (non operation)
• GH1 (Gate, Pin 4 of Q210) against ground (non operation)
• Pin 4 of U831 (OCSET) against ground (non operation)
• R1072 (non operation)
• R1118 (non-operation)
• R1118 both sides during operation - one should be 5V.

Interesting side note: NVVDD_PWRGD is pulled to 5V via 10k (R1118) - if it is kept low, that means that the ISL is actually doing "something", albeit just saying power is not good. Since PGOOD is open drain, there must be somebody pulling it low and that can just be the ISL.