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Said I was going to post this.......so here goes......I am starting to find that there are four 12k/5W resistors which are siliconed to the main ckt board that dissapate a lot of heat.......over time, the heat starts to dis-color the board until it eventually turns black...and the printing on the resistor body dissapears....by this time the carbonized ckt board has to be cut away as it is pretty much burnt up....
When I get one of these to repair and this damage has not yet formed, I cut these resistors off the board and mount new ones and raise them up so that they can't burn the board up......Also, as these units do not have a fan to help with air flow, they tend to build up heat and therefor tend to dry out the small electrolytic caps.......sometimes there might only be a couple...other times there might be 5 or 6.....usually, 1uf, 10uf, 4.7 uf and 2.2uf.....most are rated at 63V.....
.the capacitor C9 in particular, will cause the horn to sound weak or if bad enough no sound from the horn at all.....C11 and C12 will cause the unit to turn on fine but no sound........these are also drying up due to the heat and affect the mute ckt....There are other caps as well that are probably on the way out.....one has to check them all....I find that after these caps are replaced, the unit sounds much much better... and replacing those resistors is probably the best thing you can do to help prevent the board from getting burnt up.....Hope this helps somebody out in the future....
When I get one of these to repair and this damage has not yet formed, I cut these resistors off the board and mount new ones and raise them up so that they can't burn the board up......Also, as these units do not have a fan to help with air flow, they tend to build up heat and therefor tend to dry out the small electrolytic caps.......sometimes there might only be a couple...other times there might be 5 or 6.....usually, 1uf, 10uf, 4.7 uf and 2.2uf.....most are rated at 63V.....
.the capacitor C9 in particular, will cause the horn to sound weak or if bad enough no sound from the horn at all.....C11 and C12 will cause the unit to turn on fine but no sound........these are also drying up due to the heat and affect the mute ckt....There are other caps as well that are probably on the way out.....one has to check them all....I find that after these caps are replaced, the unit sounds much much better... and replacing those resistors is probably the best thing you can do to help prevent the board from getting burnt up.....Hope this helps somebody out in the future....