RX 6600 XT Missing Phase Issue – IR35217 Controller Diagnosis
After working on quite a few RX 6600 XT cards, one issue that shows up more often than expected is a missing VRM phase. This particular card came in with a strange behavior — it would power on, sometimes even give display, but the moment any load was applied, it would crash instantly.
At first glance, this looks like a typical unstable GPU, but once you start probing, the real issue becomes obvious.
🔍 What I Found on the Bench
The first thing I checked was the VRM section. On a multi-phase design like this, all phases should be switching evenly. But here, one phase was completely dead.
- No switching activity on one phase
- Other phases working normally
- No visible damage on MOSFETs
- No obvious short circuits
This is where many people go wrong — they immediately assume a blown MOSFET and start removing components. But in this case, everything downstream looked fine.
⚡ Why a Missing Phase Causes Crashes
When one phase drops out, the remaining phases are forced to carry extra load. The GPU might still boot, but under stress, voltage becomes unstable and the system crashes.
So even though the card "works", it is not actually stable.
🧠 Tracing the Problem Upstream
Instead of focusing on the power stage, I traced the PWM signal for the dead phase back to the controller — U505, which is an IR35217.
That’s where things started to make sense:
- No PWM signal reaching the dead phase
- Other phases receiving proper signals
- No physical damage on PCB
At this point, it becomes very likely that the controller itself is the issue.
⚠️ Why This Isn’t a Simple Replacement
Now this is where it gets tricky. The IR35217 isn’t just a basic chip — it’s programmable. It communicates over I2C/PMBus and depends on configuration data specific to the GPU model.
So if you just replace it with a random new chip:
- The card may not start at all
- Voltage behavior can be incorrect
- You risk damaging the GPU core
This is not a "swap and done" situation.
🔬 What I Always Verify Before Replacing It
- Check if the PWM output pin is actually dead
- Compare with working phases
- Confirm I2C activity if possible
- Rule out configuration-related issues
Sometimes the chip is fine, but not generating signals due to logic conditions or missing enable signals.
🛠️ Practical Repair Approach
In most reliable cases, the safest method is to use a donor board with the exact same model and transfer the controller from there.
That way, you retain the correct configuration and avoid unpredictable behavior.
💡 Real Insight from Experience
A missing phase does not automatically mean a bad MOSFET. In fact, many RX 6600 XT cards I’ve seen had perfectly fine power stages — the problem was always upstream.
Jumping straight to removing MOSFETs is one of the most common mistakes. If the PWM signal isn’t there, nothing downstream will work anyway.
⚠️ Important Notes
- Always verify PWM signal before replacing components
- Avoid random controller replacements
- Do not power the card repeatedly during instability
✅ Conclusion
This kind of issue highlights how modern GPUs rely heavily on controller logic, not just power components. A missing VRM phase can look like a hardware failure, but often the real problem sits in the control side.
Taking the time to trace signals properly can save a lot of unnecessary work — and prevent damaging a repairable card.