Hi guys!
I'm having problems with my band mates bass amp head.
It stopped working one day.
I found that one of the driver transistors was dead (it was not short circuited but hFe could not be measured) so I changed that. The fuses were blown and some 0R resistors as well (they are used as jumpers on the PA pcb).
This far it was straight forward but now the frustrating part comes.
If I turn it on (with a light bulb in series with 220VAC cable) without any speaker load and attach speakers later - it works fine. If I turn it on with speaker connected - it trys to jump to positive rail voltage (the light bulb limiter does not allow it to do that). Judging from the burned 0R resistors it has been run with only one rail connected for a while. All the trannies are fine now (desoldered and measured hFe for all of them).
Has anyone expirenced such a strange PA behaviour?
I'm having problems with my band mates bass amp head.
It stopped working one day.
I found that one of the driver transistors was dead (it was not short circuited but hFe could not be measured) so I changed that. The fuses were blown and some 0R resistors as well (they are used as jumpers on the PA pcb).
This far it was straight forward but now the frustrating part comes.
If I turn it on (with a light bulb in series with 220VAC cable) without any speaker load and attach speakers later - it works fine. If I turn it on with speaker connected - it trys to jump to positive rail voltage (the light bulb limiter does not allow it to do that). Judging from the burned 0R resistors it has been run with only one rail connected for a while. All the trannies are fine now (desoldered and measured hFe for all of them).
Has anyone expirenced such a strange PA behaviour?