Sony 9-51 with vertical problems

[AlanInSitges]

Hello everyone,

I picked up a little 9" Sony set from the mid 60s at a secondhand store the other day for 20€. Before I bought it I turned it on briefly and it powered right up save for a very messed up vertical sweep - about a dozen broadly spaced lines in the center of the screen that got closer together as they reached the bottom. I figured great, an easy recap and I'll have a cool little Sony.



Well once I cracked it open I was surprised to see that every single electrolytic from the vertical oscillator to the vertical output had already been changed. My guess is that when it went bad the owner took it to a repair shop who went through changing those caps, got to the point where he didn't know what was wrong, and told them it couldn't be fixed. Shit. As a bonus it's missing about 60% of the screws that hold it together inside.

I've got the Sams, and gone through and checked voltages on every transistor from oscillator to output - they are right on the money. The yoke ohms out as it should according to the Sams. Vertical seems to be on frequency because when I feed it a signal and adjust the V hold I can watch it roll and lock just as it should. It's just that there are only about 20 scan lines on the screen (they move a bit when adjusting VSize).


(click to embiggen)

I decided to have a look at the waveforms and here's where things got confusing for me: starting at the collector of the vertical output and working my way back:

- V out collector: waveform looks pretty close; it's about 10% low on amplitude


- V out base: waveform looks pretty much the same as what's on the collector, which it shouldn't. Amplitude is about right, a bit low.


- V driver base: waveform looks pretty much the same as what's on the collector, which again it shouldn't. Amplitude is 50% low.


- V osc collector: waveform looks nothing like what it does in the Sams. Amplitude is correct.


Here's the most confusing part: Sams says the waveforms are taken with 30Hz sweep on the scope. My scope has s/div so using the cursor function I selected a single cycle of the waveform and it tells me that from driver base to output collector all the waveforms are aprox 480Hz. Stick a pin in that for a second, and going back one more stage to the vert oscillator I check the collector and the waveform is a mess but this time it says they are at close to the correct frequency.



I've been reading up on blocking oscillators in Gulati's book and have to confess I wasn't able to retain enough to apply it to what I'm seeing in the Sams.

So, questions:

Is this 480Hz thing a wild goose chase that I'm on because I don't know how to use my scope correctly? If it's not, what could possibly be going on in that circuit to cause the frequency to multiply 20X between the vert osc and the vert driver? And if that's what's going on is it safe to assume that's the reason for the malfunction seen on screen?

If on the other hand it is a wild goose chase would someone please by kind enough to take me by the shoulders and gently point me in the direction I need to be looking.

Thanks.