Re: Repairing my Tektronix 454 oscilloscope need some advice
Victor,toggle quoted messageShow quoted text
Obviously there is not enough secondary HV, or a diode is bad. If you remove the plastic cover of the HV box you can access at least one diode which is connected to a hot winding end (I don't remember which one, I think it has been mentioned in another recent 454 thread). With 1 V pp over the primary you could view the wave form at that secondary winding, using a 10 M (and 10X) probe. Then a bad (open) diode plays no role.
I estimated the primary impedance (about 10 R) by comparison of amplitude (1 V pp) with the open-circuit output amplitude of the 50 R generator. Did you also do such? Maybe tomorrow I will (just for fun with my 7854) view both voltage across and current into the primary. With the 7854 keyboard calculator it's easy to determine reactive and real input power to primary. I guess it will mostly be real power because of the (cold!) CRT filament load. (Of course the phase shift between voltage and current can be viewed on an arbitrary scope, without storage or calculator).
You might also view the collector waveform during normal operation. The 0.22 A current seems to be small and probably indicates that Q1430 can not deliver enough power to increase the oscillation to normal level; either because a fault in the feedback circuit (resistor string to Q1414 etc.) or a too heavy secondary load (shorted HV cap?) or ...(?)
On Wed, Feb 19, 2020 at 07:55 PM, Victor wrote: