Electronics > Repair

GW Instek GOS-6200 200MHz Oscilloscope - repair log

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tautech:

--- Quote from: sean0118 on December 05, 2021, 06:38:56 am ---
--- Quote from: tautech on December 05, 2021, 06:26:39 am ---How much additional resistance do you envisage needing in series with the trimmer ?
Could it just be things has drifted some and their totals marginally exceed spec ?

--- End quote ---

I guess it probably isn't that much as the trimmer is only 1k, so maybe a few more 100Ohms? I might give it a go and report back.
--- End quote ---
It could be the trimmers need some exercise too and some also give them a drink of IPA or Deoxit.


--- Quote ---I've also been recapping that area of the board, but surprisingly difficult. The pins of the 47uF are bent flat against the board, I've damaged three pads already even after trying to straighten the leads out, they just pull the pads with them. I have a repair kit though.  ;)

--- End quote ---
Yeah that's a pain when legs are hard bent over generally for wave soldering and probably with that Pb free muck in which case you'd be well advised to flood the joint with some leaded solder first to lower the melt point to help save ripping pads up.

sean0118:

--- Quote from: tautech on December 05, 2021, 06:54:02 am ---Yeah that's a pain when legs are hard bent over generally for wave soldering and probably with that Pb free muck in which case you'd be well advised to flood the joint with some leaded solder first to lower the melt point to help save ripping pads up.

--- End quote ---

The 47uF seem particularly bad for some reason, not sure why, all the others came out okay.

I replaced the 2.7k in series with the 1ms trimmer with a 3.3k. I can now trim it at 1ms, but the problem is the trace stops at 9 divisions and doesn't reach the edge of the screen. Then if I switch the time make generator and scope to 1us it's out again.

I'll need to think about this a bit more, I thought it would work but didn't really have the desired effect.   ::)






tautech:
H Gain would seem like it needs adjusting to at least have a blank sweep extend past the graticules.
It's between Q905 and 906 in the Hori Preamp schematic on P26.

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