But where is made the +12v on this Hameg312?

[GGMM]

Hello,

This oscilloscope is repaired (pb of trace return that was visible), but I still have one last anomaly.
Y amplification gives traces of 50HZ. Example if we visualize a signal it undulates.
I tested the power supplies, no 50hz except on the test point +12v of the pcb vertical amp (about 20mv).
No matter how I look at the diagram, I find all the tensions, but I can’t see how this +12V is created.
Maybe I have a low view LOL.
Can you clear up
see the schématic on this pdf at the end
thank you for your help

[jonpaul]

post photo of screen with no input or GRD

Jon

[GGMM]

Hi,

I found out where the +12v is.
This is from +24V with Zenzer (see drawing)
On the other hand, I don’t think it comes into play on the Y amp part, which seems more powered by 24V and 140V.
I’ll give you a video of the anomaly
cdt

[GGMM]

Hi,

Pb solved.
Resuming X and Y settings.

However, I have one more question.
I manufactured a resistance of 90MOhm by sering 15 resistors  of 0.5 W to be as close as possible to this value.
If I use my other oscilloscope with a probe (x10) so in theory 10 MOhm, I would like to do a quick test of the THT value (-2000V), so this should make a dividing bridge and the oscillo display -200V. r1 = 10mohm r2 = 90mohm, so the dividing bridge r1/(r1+r2)
Possible?

cdt

[George Edmonds]

Hi

Will work at DC, but will not be compensated for AC.

It is possible to get 2kV X100 scope probes from the likes of eBay for little money, just don’t hand hold them when in use.

I do have one which has proved very useful, just be very careful with them.

G Edmonds

[GGMM]

hi,

I did the test with my handmade probe. That’s great, I had exactly -200V on my oscilloscope, proof that it divides well by 10 the THT of -2000V.
I took the opportunity to check the time base and amp Y.
Everything seems okay.
It’s actually nice to work on these old materials. Easier to repair. LOL

cdt