This post is a follow up to the other really useful posts on MX4,6 & 7000 chassis problems.

I initially added something to this thread http://forum.beoworld.org/forums/p/12167/204175.aspx#204175 but after addressing all of the usual suspects (dry joints capacitors etc) and further investigation I think that I have a fault that is not covered by this or any of the other MX problem threads.

All capacitors and possible dry joints mentioned in Martin's informative post here http://forum.beoworld.org/forums/p/24571/185027.aspx#185027 have been changed/resoldered.

The symptoms are that the set "sometimes" won't come out of strandby i.e. red light on, press TV, red light off and sound of degauss, 400ms later red light on.

Measuring voltages with DVM I can see all secondary power supply voltages come up and then go again when TV is pressed.

As per service manual I suspect either I2C bus error or PSU overload error.

As per service manual, with the TV in standby I make a constant short of the service mode plug and press TV and then remove the short. 

Nothing happens but when I scope P60-10 on the A/V switching I see the startup squarewave at its last point of the power fail loop before it returns to the CPU.

With the TV still in this mode I began to study the circut diagram but then after about 1 minute I hear the sound of static around the tube and the TV just suddenly starts working.

I again short the service mode plug and the last error reads 8C (13IC2 Deflection Controller).

TV now switches off and on normally but I know that within a few days the fault will have returned

I have tried freezer spray on 13IC2 (and all other chips on 13...) and also tried vigorously shaking the chassis when both off and on but it had no effect.

The next time the TV enters its won't come out of standby state I need to find out whether the PSU is really up when you turn it on with errors ignored but I suspect that it is.

I am therefore left thinking that the fault is somwhere in the horizontal drive and that what I really have is a I2C bus error as reported.

Do the experienced members agree with my analysis and can anybody offer any tips about where to look next or how to provoke the fault into something that can be tracked down?

Kindest regards

Richard

Try to replace the 82C55 PIO chip on the cpu board. This chip causes also this error message since some timing informations are lost.

The MX4000 in my workshop had a defect 82c55 chip and had exactly this bad behaviour like your MX7000.

Martin

Thanks for the advice Martin.

My local shop stocks these and they are ony 4.50 euro so I will pick one up tomorrow.

Richard