Hmm i also have this problem
Thank you for the suggestion on fast pulse checking , i might have to build the box and try it
Interesting thing is i have lifted the resistor in the emitter of the two driver transistors and i get a rock solid 42.x V across the inverter driver circuit electrolytic.
This is between the two test points. I have not hung a bulb on it to see if it holds up but i expect it will. i also need to check the waveforms on the TDA chip but i assume alright. I assume that something is loading the driver transistors of the inverter from starting up or one of the inverter transistors is just dumping full load current to the 0.2 ohm resistor which shuts down the pre-reg.
So i removed all secondary loads one at a time including filament wires and the sneaky 5 volt bleed ...still no go.
Checked all diodes across the secondary and appear all ok. I have now removed the transformer completely and of course the 43 is still there.
I have put an inductance meter on the primary and it measures 36mH across the two outer windings with the windings joined for the centre tap.
Interestingly if i measure the windings separately i get 6.58uH per winding on the primary which is strange.
Next up i will put a signal genny on it and see what the secondarys measure although i suppose i should measuer at 20khz and not a few k's.
Like the 24ohm resistor check as a substitute for the secondary but how does this oscillate with no base drive from the primary feedback circuit?
this all points to the rise time ringing check but if it fails i guess in the bin it goes. The transformer seems vacuum potted and impossible to rewind.
Forgot to add. This all started with an excessive amount of jitter on the display and then the familar cycle of inverter tring to start with the "squeak" at 12hz
Update.
This is alittle bit of a mystery
Checked the inductances on the transformer and this is what i get:
primary 3 and 4 shorted out with a clip ..normally connected via pcb
between 2 and 3 6.85uH
between 4 and 5 6.85uH
between 2 and 5 36.5mH
resistance between 2 and 5 0.3 ohms
secondary 12-14 41.2 mH
14-16 41.2mH
13-15 36.5mH
12-16 46mH
13-14 25.2mH
14-15 25.2mH
tried to measure the hv to what i think is pin 10 and shows 500k resistance and zero inductance
Maybe there is a cap in the way?
worrying is the inductance measurement on the primary between the centre tap and a collector of a transistor would be 6.85uH
This seems too low but if anyone out there can tell me otherwise i would be grateful.
If i join 3 to 4 as it would be normally on the pcb then the outer 2 to 5 read mH but that is not what would be seen by a transistor collector.
7uH would saturate very quickly i think.
Is this broken?
Think i have found my problem.
Did a frequency test of the transformer putting 1 v at 600 ohms between pins 2 and 5 with 3 and 4 shorted.
Ran it at one k and teh outputs were all low but there and in proportion but a little low. Increased frequency to 10k and level doubled. Increased to 20 K and not much change. On the face of it it looks fine, however on deeper looking i notice a hairline crack through the ferrite core. Now it makes sense. Inductance drops and primary current increases to maintain same volt secs across core . Current increases beyond limit on current sensing resistor and trips main inverter supply pre reg.
I suppose if i cou;d find an identical core i could replace but is probably a long shot.
Need to look for a spare transformer now.