Quote:
Originally Posted by RogerEvans
ZUP comes from the logic chip K501 and with moderately slow speed speeds the beam should be unblanked nearly all the time. Check that the signals on either side of R503 and on pin 5 (Q) of K501 are all about the same and switch between a low of less than 0.5V and a high of at least 2.5V. Pin 6 (Q bar) of K501 should be the same signal but in the opposite phase. If pin 5 spends most of its time low then either K501 has failed or it is being reset too soon by the CLR input on pin 1. You probably need to use the dual trace feature on the Scopex to look at pin 5 and pin 1 at the same time - triggering on the pin 5 trace only.
|
Hi Roger.
The pulse on both R503 and pin 5 of K501 has the trough of the pulses sitting on 0V and the peak at close to 5V so that would appear to be OK.
The pulse changes only in a subtle way when the Add/Chop and Dual buttons are depressed.
Also, the ramp waveform seems unaffected by the Add/Chop and Dual button position but as I say if these two buttons are pressed then the scope seems to be fine. Also the ZUP signal is essentially the same for all combinations of Add/Chop and Dual switch settings.
One thing I did notice is a variation between modes on the signal marked Alt. Pulse AMP. The DC level and pulse amplitude are different but the pulse width is the same.
If both Add/Chop and Dual buttons are in then the trough of the signal sits on 0V with an amplitude of 3.6V.
When Add/Chop and Dual buttons are out, the trough sits on a DC level of +1.6V and the peak is at 3.6V so an amplitude of 2V. Whether this is significant I can't tell. I can't quite make out where the Alt. Pulse AMP signal comes from and I have to admit to being perplexed at this fault. It would be great to sort this scope out as it's been a dependable old friend in the workshop.
Regards
Symon