Re: Another scope 7854

Joe Laffey
 

yOn Thu, 4 May 2017, David @DWH [TekScopes] wrote:


A shorted C375 shown on schematic 4 would cause about that much high
gain. A shorted C445 shown on schematic 3 could cause it if R445 is
adjusted to a low value.
Wow! I want to be you when I grow up! C375 was indeed shorted. I understand why this affects the gain, and would be able to follow it better if it were a modern OpAmp rather than discreet transistors (I can't visualize those as well yet).

I got a suitable replacement from my local store and will swap it out later today.

The occasional triggering glitch I think must by the cam finger switches on the AC/DC/GND/DC Offset switch. I got them to go away on channel 1 through exercising the switch, but channel 2 still has this glitch. I need to figure out the best way to physically access these to clean them with as little disassembling as possible. Will have a look at that too.

Thanks so much for the help.

Also, in addition to the averaging the 7854 does have the cursors and measurements built-in over the 7904. They are actually relatively easy to use, about the same as my 2232, though having a knob for the cursors is nicer than the buttons.

--
73
Joe Laffey
The Stable
Visual Effects
http://TheStable.tv/?e40768M/

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