Problem with Technics SA-DX850

SA-DX750 (sister Model to SA-DX850). Showing error code F70, after a few minutes running. Checking the power rails revealed +5VA and +5VD, on the Digital Circuit Board 'A', dropping to about 2V, when fault occured. F5, T1A, on the Sub-Transformer Circuit 'M', was subject to occasional blowing. The problem was traced to an intermittent break, in the printed circuit board conductor, in the vicinity of Q1702 (+5VD regulator) collector, on the Digital Circuit Board 'A'.. Repairing this cured the problem. Note that removing F5 (above), or disconnecting CN702, CN1000A or CN904B, on the Digital Circuit board 'A', also causes this error code to be displayed. Failure of the audio output ICs, IC651 & IC801, is apparently the usual reason for this error code being dsiplayed, but it is worth checking the power rails viz. +/- 25V (Fuses F3 & F4, T6.3A, on Sub-Transformer Circuit 'M') +/- 55V, +/- 14V etc.

This usually means "protect". If you have no speakers connected at all and the unit still starts up that way, then there is a problem with the final output stage of the amplifier. Usually this means that the output transistors are shorted. I believe that these units use "amp-pacs". These are large ICs attached to the heatsink and usually start with RSN. If so, these usually cost between $75-$125 each with 2 different ones in the amp.

To determine which one has failed, I would suggest that you have this checked at a service shop.

Dan

I cant get my main speaker jacks to work, just surround sound jacks!?!