I use a SVGA monitor with my Amiga. Over the last few months it has been exhibiting some strange faults such as flickering and only showing 2 colours. What can I do?

This was a question posed on the Classic Computers mailing list so here is a combination of all the answers to the question. These attempt to solve the problem if you believe that you are able to repair monitor hardware. If not, either take the monitor back to whoever you bought it off if it is still under warranty (the best solution before you try to fix it yourself) or buy a new monitor.

It is possible that it could be a bad flyback transformer that is almost dead. This is consistent with the flickering although it could also be a number of other things. Go to http://www.repairfaq.org/~filipg/ for the info you need (although it seems to be down at the moment due to the amount of data pulled from that site exceeded the limits set by the ISP). The mirror sites can be found by a search of sci.electronics.repair. Read the safety warnings before you pull the case on a monitor. There are dangers in them - high voltages (not just the EHT to the CRT, but also mains), the high-vacuum CRT that could implode (although it's unlikely), etc.
However, unless you have a high voltage probe to test the voltage going to the cap on top of the picture tube you'll have to guess whether the flyback is at fault. Missing colours are certainly not the flyback, though.

Missing colour (only 2 of the 3 guns working)
Bad cable or PC plug (bent pin)
Dry joints on the CRT base panel (Where the video amplifier normally is)
Defective components (transistors, LM1203 chip, etc) in the video amplifier CRT (unlikely)

Horizontal line (only)
Vertical output chip
Capacitors near the vertical output chip open/shorted
No power to vertical output chip (maybe fusible resistor O/C)

Vertical line (only)
If EHT comes from the horizontal output, then O/C yoke, connector, or coupling components.
If separate EHT generator (fairly common in monitors with multiple scan rates, including even EGA), then horizontal output transistor, drive to it.

Blank screen, power on light normal
Look for glow from CRT heater. If missing, check supply (maybe from the flyback, maybe from the main PSU) and heater continuity

Check EHT with a special EHT meter. Expect about 25kV on a colour monitor, about 12kV - 15kV on a mono one. If missing, check flyback, horizontal output transistor, etc
Check other CRT voltages. If any are missing, trace back to the source (probably from the flyback).
It's possible, although rare, for a video amplifier fault to bias the CRT beyond cut-off. Sometimes turning up the 'screen' control will get a raster in this case.

Blank screen, power light flashing about once a second
The main PSU is tripping (assuming this isn't some infernal power-save mode). Most likely cause is the horizontal output transistor shorted, probably due to a shorted flyback.

Main fuse blows violently
Short on the primary side of the PSU :
Chopper transistor, bridge rectifier diodes, degaussing posistor, chopper control module, etc. Sort this out like an SMPSU

Flickering, especially when case is tapped
Dry joints (could be just about anywhere). Often a complete resolder is the quickest way to solve this.

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