Hi,
The front panel input selector on a Lineartech AX-4400 is stuck on "FM". When another input button is pressed and held, the associated LED lights up. The FM light stays on during this process.
About the front panel:
I checked all of the mechanical micro switches for continuity and proper function. They are all in great shape, having infinite resistance when open.
About the main board:
The switch traces lead to a ribbon cable, then directly to an LC7818 function switch IC on the main board. How do I test to see if the IC has gone bad?
PS, I have tested for shorts between the ribbon cable and solder pad contacts.
The front panel input selector on a Lineartech AX-4400 is stuck on "FM". When another input button is pressed and held, the associated LED lights up. The FM light stays on during this process.
About the front panel:
I checked all of the mechanical micro switches for continuity and proper function. They are all in great shape, having infinite resistance when open.
About the main board:
The switch traces lead to a ribbon cable, then directly to an LC7818 function switch IC on the main board. How do I test to see if the IC has gone bad?
PS, I have tested for shorts between the ribbon cable and solder pad contacts.
Agreed. It seems from similar posts on a few audio repair forums, that the 7818 chip is prone to failure and consequent loss of selector function. Removing a 30 pin chip may not be a simple task for the inexperienced though. You'll need patience, care and a quality temperature controlled iron + fine solder-wick braid to remove the IC without doing collateral damage by prolonged overheating, such as lifting tracks from the PCB.
Pro's might use specialised hot air or copper bar heating heads for this type of work but you may find that buying the gear and gaining experience in using it is more expensive than the job is worth to you so it may well be cheaper to enlist a repair technician to do the work.
Pro's might use specialised hot air or copper bar heating heads for this type of work but you may find that buying the gear and gaining experience in using it is more expensive than the job is worth to you so it may well be cheaper to enlist a repair technician to do the work.
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