Mono instability in Y direction

Issue

Mono instability in Y direction.

Environment

Titan 80-300

Resolution

These are possible resolutions for the issue:

• Replaced 3 boards of GMS, DPA and SDCA.

Cause

These are possible causes for the issue:

• Boards defective.

Details

Emitter was replaced 2 months ago, at that time FEG can’t be started, it had communication problem, replacing GMS, SES, CPB boards fixed it.
Now FEG emission current = 589 uA, before it was about 400 uA.

To determine if the instability source is HT or FEG or charging related: 

1. HT emission current = 0 uA.
2. Back focal plane check per WI-300259 at 300 and 80 kV. 
3. HT AC stability test per WI-103190 in service and normal mode by HCA X‐100 jumper, normal mode OK (< 500 mVpp). 
4. HFP test per WI-105031, Ibleeder and Imeasuring-resistor and Cascade OK. 
5. FREF test from TAD, OK. 
6. Follow WI-106115 “Mono instability TFS”, and goes to HT conditioning, not favorable. 
7. Source of instability confirmed to be in FEG (WI-306046, WI-106115).