Steve Anderson wrote:Harry, as you now have a trace/traces, forget the voltage measurements I mentioned earlier. Instead carefully measure the voltage on the wiper of the H.POS pot as you vary it from one end to the other, it should go smoothly from +8V to -8V (or the other way around). If the pot isn't easy to reach measure at C317/R353. Circuit is 'HOR AMP', Document Number TI2003, bottom left.
OK i had a look at this its 7.44 volts in my case either side again must just be my power supply voltages every thing seems a bit lower .
If it jumps suddenly from one voltage to another, (which may not be +8/-8) either the internal pot track is broken and/or the wiper isn't in good contact with the track. If this is so, the pot will need replacing. But check for dry joints or cracked tracks on the board if the pot pins are PCB mounted. The problem wll be finding a replacement as it also has the push-pull 'x10' switch, but you could opt to do without it by wiring it in the 'x1' position permanently. I find I very rarely use the 'x10' function, if ever.
This is the case around the middle correct position but with a little fiddling it does center and stay there your thoughts of the pot being worn perhaps being handled ruff sound like the case .
I think i will leave it due to its a hard one to replace and live with it i suppose i could just replace it but its a lot of work to get it out and i can still adjust it now knowing what up .
There's no harm in going around the whole instrument tapping (gently) with the insulated handle of a screwdriver to see if there are any more gremlins that might otherwise surface later. It's better to do this now while you still have the covers off. When you can soak-test it for a full day with the covers on so it gets to normal temperatures.
The tap test only effects the horizontal pot makes the trace jump but i will do the full day test and warm it back into service
With any luck you have a 25MHz dual-trace scope for five bucks and a bit of time and effort.
Steve A.
I am very happy with it as is, i mean 5 dollar dual trace scope with z axis only my 60s one can do that i don't like using it much in case a valve gos .
I just have to replace that plug at the back as it got bent from what ever knock that started this all.
We still don't know what that extra transformer does, but if the thing's working - leave it!
Yep i will live with it i bolted the little transformer back on tight so keep on power supplying what ever i am happy.
Later on you may want to check the calibration, both the timebase (time/cm) and CH1/2 (V/cm). But that can be left for now.
Thats something i didn't think of but with my interests being slow scan and nbtv mainly it really only needs to be on the lower side from what the scope can do ,but i will look into how close both channel time bases are .
Thank you again Steve for you help here it made fixing it much easier !