Hello. I’m working on my TX 870 and having a few issues. The left channel dropped out and the main fuse blew. I found a cracked bridge rectifier and it was toast. Replaced it along with all the outputs on the left channel. Found some bad transistors on the main board and also replaced the drivers. For some reason I’m getting full rail voltage at the VCT test pin. This won’t allow the protection circuit to close the relays. It should be in the millivolt range. The right channel is fine. DBT goes bright as the main power relay closes and then opens and the DBT goes dim. Constant cycle. I’ve got the service manual and have replaced the emitter resistors, and several other bad components that tested bad. Any ideas ? The output transistors are fine. No shorts. Thanks in advance. The only other thing I replaced were the 2 caps in the protect circuit.
First: Please show the circuit diagram. Then measure the related voltages and compare with the values given in the diagram.
Best regards!
Best regards!
Replaced some more bad resistors and transistors and now I'm getting around 35 VDC on the 56 v rail. R540 will melt and several resistors will fry as well if I dont use my DBT. There is still a short or a bad transistor in the amp circuit for the R channel. Voltages at the Output tr. are also high. I'm getting too much V to test pin VCT on the R channel. The left channel seems normal. The full rail V from the Rectifier is finding its way to the speaker relay.