With different illumination that thing at the side of the metal structure looks always different than "normal dirt".
Perhaps that´s a production problem leading to a leaky JFET?
Degraded performance caused by an ESD strike? It presumably tested fine at manufacture.
P.S.QuoteCouldn´t assign the "M" logo...
Motorola maybe?
@Noopy,
Thanks for these nice insight pictures.
Do we actually know, who the manufacturer of Q308 is and is there a datasheet around ?
I was happy to get such an special IC!
Unfortunately I also wasn´t able to identify the manufacturer. Couldn´t assign the "M" logo...
I will join the club soon!
What it does is turning on some LEDs and digits on the front for 2-3 seconds. Power rails are okay, but the motorola microcontroller does not run the crystal. Now I am waiting for a new crystal.
But anyway, has anybody seen such symptoms?
Thanks,
I also had a broken crystal, but the one used by the ADC, not the one used by the micro. I find it strange the leds & digits go again out after 2-3 seconds. That does seem like the micro is doing something, or a power rail that shuts down (overload?).
What I also see is that the display board does not produce the button release pulses. Its strange because the display board has the power supplies and there is nothing there that could likely go wrong.
I measured voltage between U309's pin 2 and 3. It was 10mVolts. When I have applied a voltage to the input, the voltage was the same. But while doing this the displayed value changed.
Also I have measured the output of this opamp and the output was constantly -77mV while I changed the input voltage.
I measured voltage between U309's pin 2 and 3. It was 10mVolts. When I have applied a voltage to the input, the voltage was the same. But while doing this the displayed value changed.
Also I have measured the output of this opamp and the output was constantly -77mV while I changed the input voltage.
Did I understood you correctly that, when applying a voltage between pin 2&3 of U309 the display changes, but when applying a voltage to the input terminals of the 617 no change is seen on the display. This would indicate something is probably wrong with Q308...
The W303 jumper is for coarse trim / compensation of offset of the FET pair. Remember where it started and watch out for ESD as the FET can be ESD sensitive.
10 mV across the input of U309 is normally too much - especially for an LT1012. So the U309 should be close to one side of it's supply (bootstrapped +-5 V) With a fixed output, there should not be much movement for the bootstrapped supply - more like close to +-5 V. The 90 mV shift is not much.
Yes, I was not so accurate. So I have only applied voltage to the input of the instrument. The reading on the display changed only because of the probing impedance I guess.
So any voltage on the triax input has not effect. But zeroing works fine.
So I have only applied voltage to the input of the instrument. The reading on the display changed only because of the probing impedance I guess.