Guest
This is the same scope as in the "Cheap And Easy 6.3 Volts thread.
It has mucho problems in the vertical. I found a couple of shorted transistors and wondered at first why ? The thing WAS working fine but then IT WAS ARCING ! No wonder.
So I am muddling my way through the stages running down some clipping and what was an offset in channel 2. There is a blocking oscillator that feeds a multivibrator for the channel switching. The oscillator isn't running. It was alwayts stuck in channel one. The transistor, Q260 was dead shorted all the way around. How the arc got there is, well Ithink it should have blown more shit, and it might have.
Upon the replacement of Q260 it now switches channels, in alternate. The switching is totally erratic and I haven't investigated the pulse coming from the horizontal plugin yet. (it is a 3A1, and the print is not available online) But it does something, which is more than it did before. It still doesn't oscillate so therefore it won't do chop mode. Apparently the shorted Q260 was shorting out the pulse form the horizontal but now it is passing, somewhat. The channel switching is not instigated by the horizontal pulse, it is random. It is not even frequency dependent. And of course in chop it doesn't switch at all.
There is a little transformer in that oscillator circuit, could the arcing have shorted it out ? that might explain things. the pulse is compressed, and no oscillation, that symptom is about what would happen if the transformer has a shorted winding. The other problem is finding things. Not only am I half blind, I got used to circuit boards and it is now harder for me to follow point to point wiring.
And both channels are clipping before the signal hits Q134 and Q144 as evidenced by the fact that the trace is very large at the 10 mV setting due to sections 5F and 5R of SW110, the vertical gain switch.
I have checked the power supply. All regulated voltages are tight but the unregulated voltages are low due to low line voltage. It comes up when I shut off the electric heater that is on the same extension but that has no effect on the scope, it acts the same.
There is a 3A1 on eBay for $ 10 but it is marked for parts only. I wonder how many of these scopes got the arcing transformer blues.
The first time with the original power transformer there was nothing hooked up to the vertical input. This time there was and that is probably what sent that arc through the system. Ten bucks isn't bad, but if I get the same problems, plus pay $ 19.71 in shipping it is not worth it. This is supposed to be fun, I have other scopes to use, much simpler and a bit more bandwidth. I like to play around with the dual time base. Pick some complex waveforms to pieces n shit.
I got some wrong voltages that don't really make sense, but that is typical of when things arc. I'll list them later when I put it back up. I had to set it aside for ow, but any good ideas and I'll put it back up.
In the meantime if anyone has any ideas I am all ears.
It has mucho problems in the vertical. I found a couple of shorted transistors and wondered at first why ? The thing WAS working fine but then IT WAS ARCING ! No wonder.
So I am muddling my way through the stages running down some clipping and what was an offset in channel 2. There is a blocking oscillator that feeds a multivibrator for the channel switching. The oscillator isn't running. It was alwayts stuck in channel one. The transistor, Q260 was dead shorted all the way around. How the arc got there is, well Ithink it should have blown more shit, and it might have.
Upon the replacement of Q260 it now switches channels, in alternate. The switching is totally erratic and I haven't investigated the pulse coming from the horizontal plugin yet. (it is a 3A1, and the print is not available online) But it does something, which is more than it did before. It still doesn't oscillate so therefore it won't do chop mode. Apparently the shorted Q260 was shorting out the pulse form the horizontal but now it is passing, somewhat. The channel switching is not instigated by the horizontal pulse, it is random. It is not even frequency dependent. And of course in chop it doesn't switch at all.
There is a little transformer in that oscillator circuit, could the arcing have shorted it out ? that might explain things. the pulse is compressed, and no oscillation, that symptom is about what would happen if the transformer has a shorted winding. The other problem is finding things. Not only am I half blind, I got used to circuit boards and it is now harder for me to follow point to point wiring.
And both channels are clipping before the signal hits Q134 and Q144 as evidenced by the fact that the trace is very large at the 10 mV setting due to sections 5F and 5R of SW110, the vertical gain switch.
I have checked the power supply. All regulated voltages are tight but the unregulated voltages are low due to low line voltage. It comes up when I shut off the electric heater that is on the same extension but that has no effect on the scope, it acts the same.
There is a 3A1 on eBay for $ 10 but it is marked for parts only. I wonder how many of these scopes got the arcing transformer blues.
The first time with the original power transformer there was nothing hooked up to the vertical input. This time there was and that is probably what sent that arc through the system. Ten bucks isn't bad, but if I get the same problems, plus pay $ 19.71 in shipping it is not worth it. This is supposed to be fun, I have other scopes to use, much simpler and a bit more bandwidth. I like to play around with the dual time base. Pick some complex waveforms to pieces n shit.
I got some wrong voltages that don't really make sense, but that is typical of when things arc. I'll list them later when I put it back up. I had to set it aside for ow, but any good ideas and I'll put it back up.
In the meantime if anyone has any ideas I am all ears.