Power up [[6400 Bringup Log]], and smelled something from around back. Kept investigating with nose, found smell to be strongest above the #1 CRT (left CRT). Removed front panel to expose CRT and noted large resistor with heat shrink on leads mounted into terminal strip. Heat shrink was charred. After reviewing the resistor, its schematics, and other microscopes we determined that this heating is likely normal for this mode of microscope. We could replace the heat shrink but given the temperatures involved it would probably not fare much better. ## Pictures R1 visible over top of CRT1 ![[Pasted image 20240124163027.jpg]] R1 ![[Pasted image 20240124163112.jpg]] ## Schematics Resistor is R1 in CRT DSPL(1) CKT, fed from CRT PA(1) CKT JK1. ![[Pasted image 20240124162754.jpg]] ![[Pasted image 20240124162806.jpg]] ## Thermals Investigated with thermal camera in Fast Scan full frame and Fast Scan reduced modes. Found that temp of resistor was (as expected) lower when in reduced mode. ### Reduced (after several minutes) ![[Pasted image 20240124163138.jpg]] R1 reading 425°F ![[Pasted image 20240124163219.jpg]] ### Full Frame ![[Pasted image 20240124163243.jpg]] R1 reading 626°F ![[Pasted image 20240124163258.jpg]] ## On other 63/6400 series microscopes This heating seems to be by design, despite the charred heat shrink... To see if this was common to this series, we checked the same resistor on the [[JSM 6320F]] in the next bay over and found the heat shrink on its R1 to be in an even more degraded state... ![[Pasted image 20240124163810.jpg]] ![[Pasted image 20240124163822.jpg]]