Has anyone seen this behaviour repairing Tek2000 series scope power supply?

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Behaviour

1. When power on from cold, it will fire up properly and stay on for a few minutes

2.? Once it warms up, the power supply shut down and try to on again and it continues in this on/off mode

3.? Pre-regulator out = 43V? (between TP940 and TP950)

4.? All voltages when the unit is stable for a few minutes are +8.6, -8.6, +5.2, +100 are all ok.

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What are likely problems before I start ripping the components from the circuit?

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?ttesenq@... suggested that it could be the pre-regulator MOSFET P9070.

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I though that it could be a electrolytic cap but it doe not look likely because electrolytic failure would not have allowed the unit to fire up for a few minutes

It is more likely a active component that weaken with increase temperature, so ttesenq@... could be right.?

This would mean Q947 and Q946 are also likely components

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Any other possible lead of similar experience.