This fix may be helpful to someone.
* Symptom: Low then almost no transmit power. Power meter might move up to about 1w for a short time then drop down to very low. Tx signal audible in local receiver but weaker than it should be. PA transistor bias settings seem to be OK, indicating the IRF510s are OK.
* Probing around with an RF probe indicated the burst from higher to low power was noticed on the PA transistor drain and back through the driver stage.
* DC voltage check found all were OK except the emitter of Q90. Instead of 3 volts there was only 0.9v.
* Q90 was removed and replaced with leaded transistor (I used a BC548 which is similar to a 2N3904). Used adjacent parts to solder leads to for better spacing.
Q90 turned out to be the problem. With the new transistor the emitter voltage reads normal and the rig now transmits.