Trying to fix Dse Q-1802 oscilloscope same as a PS 200

[harry dalek]

I am Trying to fix a Dick smith Q-1802 oscilloscope has also been rebranded to a Toptronic T200 and digitor Q-1802  pintek PS-200 oscilloscope.
It Started off with a dead primary on the transformer which i think was undersized for the scope in the first place .
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I replaced the dead transformer with a similar scrapped scope transformer and second for the low voltage supply as i didn't have a correct replacement
Pretty much getting correct voltages and the  scope lights up but the problem is i have no vertical position control on both channels and inputting a waveform result not correct .
No parts look damaged i replaced the 4011's and 7474's so far but it might be a transistor .
I suspect the High Negative is discharging next to any close wiring caused the problem it should of had another jacket of plastic over it as in later models , i can fix that but finding the problem on the vertical side needs looking into ..
Getting pretty much no trace  movement from the vertical position controls ,no problems on the horizontal side .

[Dave.]

Hi Harry,
also have Dick Smith Q-1802/Pintek PS-200.
My problem is no EHT. Also the 2SD880 had been removed. When a (similar) TIP31 was fitted it just got very hot with no oscillation. Got a new T-850 EHT transformer free from Pintek: same result.
All components in this area OK except one of the two EHT diodes which broke down at 50 volts instead of 1KV plus. Replaced both with 1N4937's.
Still gets hot, no oscillation.
Relaced the 2SD880 with a Darlington: now it oscillates but still draws too much plus 12 volt supply beyond what the 7812 can manage.
The 741 is fine.
Now considering a multivibrator to feed the Darlington's base, ignoring the 741 EHT regulator circuit and T-950 feedback winding completely.

Would appreciate any ideas from others.  Probably should have started a new topic but don't know how to do that.