2016-09-21 22:27 GMT+02:00 Pete Lancashire <pete at petelancashire.com <javascript:_e(%7B%7D,'cvml','pete at petelancashire.com');>>: I cannot find anything mentioned about character blanking in the circuit description. I read this on the topic "Alphanumeric Display": "Refer to the display control block diagram (Fig 6-13). The display coordinate position is generated through the digital-to-analog converters (X DAC and Y DAC) and fed through the filter circuitry with the filtering disabled. A short time later, either SOT is activated to print a cursor refresh dot or ADOT is activated to print a character dot. The timers for cursor intensity and character intensity are adjustable by potentiometers accessible through the bottom of the assembled instrument." Maybe this is the "A short time later" that it is not working since seems to draw instantly. But as far as In understand that timer is generated in the digital parts. Note that this is not a computer or terminal. It is an instrument per Tektronix definition... Unfortunately the detailedness of the circuit description is not up to the DEC standards in my opinion. There are no scope diagrams describing the pulses going to the Z-axis as far as I can see which is unfortunate. /Mattis

Thanks Bob for this information. I am starting to get some understanding of the machine now. I was looking in the calibration section to check the voltages on the display board. It is extremely vague on voltages there should be. "Remove J-50, which will disable the high voltage generator. Place a voltage probe to J58-3. Power up, and adjust R359 for a collimation electrode voltage of about 85V, or as specified on the crt shield" There is a label: http://i.imgur.com/ALdixwA.jpg I am not 100% sure I understand what it means. CE might stand for "Collimation Electrode" and then 75 (V) and is "storage level" the same as backplate voltage? Anyway it is said to be 164V. The calibration section says about 200V... The voltages I measured was nothing near 200V nor 164V. It was 149V on op level/backplate and 68V for collimation electrode Confusing. Anyway. When tuning the voltages there were sudden pop and a small 0.25W resistor failed spectacularly with a smelly cloud. It was the R339 47 ohm resistor connecting to the 320V supply voltage. It should not fail unless something else has failed and yes a TIP50 transistor generating the "op level" / "backplate voltage" had also failed. Short circuit emitter / base. So I need to find a new suitable transistor before continuing this. Meanwhile it would be interesting if there are any other 4051 owners out there that could maybe share what the reading of the label is on their machines. Even better if it could be measurements on an operating machine. Before the smoke escaped I recorded this short videoclip to show the behavior when typing on the machine and running simple PRINT/GOTO program. http://sendvid.com/k4s7k806 /Mattis

On 9/22/2016 12:08 PM, Charles Anthony wrote: Sendvid may be a honeytrap, but in lynx on linux, where i usually test such, it went to sendvid and sent two cookies. Probably safe.

2016-09-22 22:24 GMT+02:00 Pete Lancashire <pete at petelancashire.com>: Good idea. I will do this as soon as I replaced the TIP50. Well. Of course this could be done without working display but it would be hard to understand what is going on. Unfortunately measuring on the D/A and the filter takes that the main board is pulled out and setup to operate outside the machine.