开云体育

My current project is repairing a 8558 SA and its 182T mainframe.

The mainframe has an X problem, the bottom half (on the schematic) of the X push-pull amplifier has a low output voltage instead of 50V, ?4 transistors and some resistors have been checked: all good. Still looking ...

The 8558 has a frequency display problem, it displays "+1" instead of the frequency, I will tackle this one later.

If anyone has encountered the same problems, I am listening to your wisdom.

Best

Jose

For the record, the 182T problem was with the R38 anr R55 resistors (22.1K) one was open, the other was 30K.

Frequency display is fixed, here is how:

Mine was I suppose a early model, the frequency display is not the one described in the service manual available on the net but housed in a separate little black metallic box numbered 08558-60082 which is clamped inside the front panel.

It turned ou that the box implemented a DVM using the siliconix LD110/LD111 pair, very close to the application note or the jan 1975 ?73 magazine.

The LD110 had failed, the replacement part is easily found on ebay and make the circuit work after replacement.

What might have happened is that the 5V is derived from the 12.6V via an unregulated inverter. I suppose that when adujsting the 12.6V, one might have gone over the maximum admissible volltage for the LD110. With the 12.6V properly adjusted, I had 6.0V instead of 5.0V. I added a small 5.0V LDO for protection.

Best

Jose