Hameg HM203-6 Scope - capacitor identification

[Dave_h]

Hi guys,

Newbie but getting oldie here, hoping you might be able to help.

I've been interested in electronics in a small way for just about ever and have enjoyed repairing simple obvious faults but always feared getting down to the real component level understanding and those more invisible faults. Well the time has come to change all that. I'm learning lots about the fundamentals and how this stuff all works now, thanks to this blog and some experimenting, and I decided to buy an old scope to help with that - Hameg HM203-6 (listed as not working) and here is my first problem...

The problem with the scope is that there is no trace in the X direction, Y appears to be  fine and all controls apart from X-related work ok. I believe I've found the fault down to a shorted capacitor in the X Final Amplifier which has blown a nearby resistor.

I now have two issues.

1. The values of the blown resistor (R799) and ceramic(?)capacitor(C724) according to the schematic are both different from those fitted to the board - Should I replace like for like and ignore the values on the schematic?

2. The markings on the cap suggest it's a 0.1uf (?) but I'm not sure of the exact type or voltage. It's on a -12v line so guessing nothing too special voltage-wise, but the blue colour and shape are like nothing I can find online.

I'd really appreciate any help or advice with this so I can get down to some real learning.

Some pics of the area/schematic for reference attached.


Thanks for reading,

Dave

[EPTech]

Hi there,

Looks like the capacitor has shorted out and fused the resistor. It is a leaded MLCC (Multi Layer Ceramic Capacitor) of 100nF and judging from the size, no more than 100V, 50V is pretty standard and more than enough for your application.
I would replace the resistor with the same value as the schematic, looks alright to me. And it looks that the other rail +12, I guess has the same value, better to keep that balanced. So 6R8 sounds right.

For good measures I would also check the transistor. If you are not familiar with measuring a transistor, there are plenty of threads explaining that.

Happy repairing.

[Dave_h]

Thanks for the confirmation Pascal!

Yes I'll replace the transistor too while I've got it stripped down.

Will let you know if I succeed!

Dave

[Dave_h]

I now have a working scope! I'm sooooo happy!!

Tomorrow I shall be mostly poking around in amplifiers and seeing what really goes on