How To Safely Use An Oscilloscope On a Nanao MS9

zed7

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Hi everyone, my Nanao MS9-29A is having what I've deemed to be a sync issue.

Here's a video.

I originally thought it could be 60hz interference; however, I now think it is sync as different game boards yield different results.

The Sega Touring Car manual that specifies to scope TP1 for the sync sine waves and measure the peak-to-peak voltages.

I'm worried about doing this, as this chassis is a hot chassis and does not utilize and isolation transformer or earth ground. I believe I can hook the scope up to the on board heat sink, but NOT the frame as it should be live. I do not want to damage anything, so I am wondering if anyone has had experience with the MS9 and scoping it here.

The LA7853 is a little expensive to just replace it on a hunch, which is why I'd really rather scope the circuit first.

Thank you!
 
You need a isolation transformer when using a O-scope
on any chassis

Unless its a battery powered TV, portable stereo
battery power signal general etc


The Scope ground for AC HOT chassis is the filter cap ground
which is the same as any ground on a HOT chassis
and on a primary of a SMPS now
the secondary ground would be the same as a heatsink that is ground to the neck bd or DAG grounding strap
around the tube, which is a cold ground reference.
so you would need to be moving the ground depending which side of the SMPS your testing
for correct dc and ac waveforms.

The ground is the only concern between the chassis and O-scope
now the probe and you should find the ground banana plug type on your Scope
and not the ground coming from the probe
so to move around the chassis easy and not be limited to one area of the chassis.

Need to get the image on a fixed pattern like a crosshatch
so to see any waves in the image
and put it on any of the Video amp transistors
to collector to see if seen there.
Or along the video path
Otherwise on the Horizontal drive pulse look up datasheet pinout for IC
pointing to the Ic or dirty pots, or inputs signal to the IC

All signals should be constant if on a test pattern.
Comparing the 3 points of interest,
Video, Horiz-drive Pulse and sync separator
looking for a movement in the waveform.

Heres some tips if you haven't found where the issue is
and what frequency your testing.
and the trimmer pots are good for that frequency
like trap, HosI, SPC ETC
LUK
 
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