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Agilent 54835A scope (4 channel 1GHz / 4Gs/s) repair & uphack

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analogRF:
vertically nothing changes and all is fine. only horizontally and only inside the graticule area everything is misplaced

nctnico:
I'm pretty sure the distorted display is generated on the interface board and overlayed onto the video output:

Disconnect the flat cable connecting the interface board and the video card and see what happens. If I'm correct then the display won't show a signal with the menus (graphics) disabled.

analogRF:
OK, I'll do this today but I don't think the scope will show anything if that cable is disconnected.

I ran the Video SRAM test, Video RAM test, and Video Control Register test individually and they all pass. I believe the SRAMs are on the interface board (2 x M5416283-60 chips by OKI) because the datasheet says they have RAM and SAM operation independently.

I have ordered 2 PCI extender cables and it will take some time to arrive and then I can probe around that board hopefully. In the meantime I will try to check the tantalum caps on that board

What is that battery doing in there by the way?

EDIT:  I think the SRam here means Serial access not Static

analogRF:
what data is being kept alive in that 32KB RAM on the interface board by the battery?

I will also check the resistor arrays on these two boards. lately I have had 2 cases of resistors being open in SMD resistor arrays

analogRF:

--- Quote from: nctnico on October 02, 2018, 06:31:34 am ---I'm pretty sure the distorted display is generated on the interface board and overlayed onto the video output:

Disconnect the flat cable connecting the interface board and the video card and see what happens. If I'm correct then the display won't show a signal with the menus (graphics) disabled.

--- End quote ---

I disconnected that small ribbon cable and the scope software gave an error "the acquisition refresh rate cannot be measured" (or something close to that I forgot the exact words) and then when it got to the software it says the scope is not calibrated and none of the channels could be even turned on. the display in both cases (with and w/o graphics enabled) was blank with no trace and no graticule

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