Got another one on Facebook asking to show which way the diodes go on a Palomar 90a. OK here you go. don't know if he knows that the HV Bridge rectifier is actually 4 diodes in 1 package and THAT is what usually goes on these. 1 or more of the 4 internal diodes in the bridge shorts and causes the fuse to pop quick. Look up the schematic for a Bridge and check that the 4 internal diodes in it are good. CBTricks.xyz has the schematic of the 90a and if you look at BR1 at the bottom right, that is the HV bridge with the 4 internal diodes in it and what I suspect is wrong. D8 and D10 also on the HV PCB go to the -bias and D7 on the PCB goes to the low voltage (for the preamp and keying circuit) Also in the vid I said I wondered was that big resistor and 2 diodes coming off the HV factory. Looking at the schematic, yes it is. Those are 2 Zener diodes off the board and on the other side of the resistor D6 and D5. Its harder to test a Zener with a diode test, but it should not show a short or its bad. The 2 diodes on the relay board are just relay anti-chatter diodes. They go across the relays coil and keep the coil voltage from going back and forth thru the coil and making it.......chatter. Those cannot be properly tested while connected to the circuit as they will read bad because you will get a reading from the coil. They normally don't go bad either as they don't carry much voltage or current across them. To test them, you need to remove one leg which will disconnect the relay coil from them. The last few Palomar's that shorted the fuse that I had was a short in the Bridge BR1. You can replace the whole bridge or use separate diodes in place of a single bridge. Also, if BR1 had a short, it is usually caused by either one of the HV caps on that board or a tube had a short. Good Luck, You owe me a Happy Meal!
