so, IC2 was replaced. Output waveform is still degraded in other way. Picture shows how 980Hz sine signal looks on output.
There may be something wrong with the RAM address lines A00…A14 or the address counter setting lines S00…S14.
Is there good waveform on any frequency?
no,there isnt. For example, 1kHz sine is completely degraded.
To test the address line operation, please select 10Hz frequency range.
Click the frequency display.
Enter the frequency exact 9.9998 Hz.
Press Enter button.
Click sine on.
Check now, that there are pulses on all the address lines of the RAM IC10.
yes, there are, every address line of IC 10 has signal.
Is the generator output waveform now OK too?
no it isnt, degraded like on the posted picture.
Please check the state on pins 3, 4, 5 and 6 of IC48, IC49, IC50 and IC7.
Should be:
IC48: 0,0,0,0
IC49: 0,0,0,0
IC50: 1,1,0,0
IC7: 0,0,0,0
all there are low, except IC50 pins 3 and 4 are high.
yes, as you wrote.
Strange problem - indeed.
At the moment I don’t know how to continue…
Can you post an oscilloscope image of the “best” waveform you get on some frequency at about 500Hz.
yes, I can. But I think the best sine waveform is on the previous pic. I can get very similar waveform at 480Hz, at 500Hz is much destroyed, 520Hz is like 480Hz, 540Hz destroyed etc.
It seems like “one wave” is missing on “best” waveform…
and what about IC 6? Pins 14 and 15 also shows destroyed waveform.
It seems in the oscilloscope view also that the frequency of the wave 980Hz seems to be higher than 1kHz.
Is there similar difference at 480Hz too.
Can you check on the oscilloscope screen what is the wave period at that frequency?
okay,
here is the screen of 480Hz.
and output frequency is 640Hz
The frequency seems to be wrong (it is >500Hz).
To check the timing generator, please select the frequency range 0.1Hz.
Click sine on.
Check the pulse frequency on pin 20 of IC22.
Should be 320Hz (period 3.13ms).
its about 330Hz, changing 1 or 2 Hz up and down
The frequency should be exact 320Hz.
Please check it on other ranges too:
1Hz range: 3200Hz
10Hz range: 32kHz
100Hz range: 320kHz
Is there equal error and the variation?
1Hz range : 3199Hz
10Hz range : 31994Hz
100Hz range : 319942Hz
Seems to be OK.
One possible cause of the problem may be the RAM IC10.
The waveform data is stored to the upper section of the RAM.
The amount of the storage depends on the frequency.
Please check at 490Hz.
At this frequency nearly all the RAM is in use.
What kind of waveform you get?
on the address pins?
I meant what does the generator output waveform look like?