Philcogrump
Experienced Member
Anyone here know about those large Tektronix computers back in the late seventies? I have a ~1977 Tektronix 4052, which is said to be one of the best graphics systems in its day. Unfortunately, it does not work and I have very little experience with anything like this computer, so I'm not quite sure how to fix this.
When I first acquired it, it "seems" to start up, all indicator lights (BUSY, I/O, POWER, something else) would come on, then all but the POWER goes off, but nothing on the screen. I later figured out the display board and checked the parts, then turned up the HV output and the bias, then got a visible dot on the screen. Moreover, when the computer starts up, the dot would appear in a random spot (usually to the right) then after the indicator lights go off, the dot is reset to the very center, and that is about it.
After looking through the schematics, and with some help from a friend who has experience with Tektronix systems, it seems that the RAM might not be working (dynamic), so there was the possibility of the clock/refresh signals not working well. I checked the output of the main clock signal with an oscilloscope, and all I found was a weak 50MHz (clock crystal is 49mhz) signal, which was only about 100mV pp. I was expecting something like 5V pp, and another friend suggested I replace the buffer IC (74S04 hex inverter); so I did with a socket, and plugged in a 74LS04 since that was the only chip I had equilavent to the 74S04. Unfortunately, the computer stopped starting up the way it did before, all indicator lights come on and nothing seems to "reset" so I think I screwed up the clock signal, though it looks exactly the same on the oscilloscope (100mV pp).
Any ideas or what did I do wrong?
When I first acquired it, it "seems" to start up, all indicator lights (BUSY, I/O, POWER, something else) would come on, then all but the POWER goes off, but nothing on the screen. I later figured out the display board and checked the parts, then turned up the HV output and the bias, then got a visible dot on the screen. Moreover, when the computer starts up, the dot would appear in a random spot (usually to the right) then after the indicator lights go off, the dot is reset to the very center, and that is about it.
After looking through the schematics, and with some help from a friend who has experience with Tektronix systems, it seems that the RAM might not be working (dynamic), so there was the possibility of the clock/refresh signals not working well. I checked the output of the main clock signal with an oscilloscope, and all I found was a weak 50MHz (clock crystal is 49mhz) signal, which was only about 100mV pp. I was expecting something like 5V pp, and another friend suggested I replace the buffer IC (74S04 hex inverter); so I did with a socket, and plugged in a 74LS04 since that was the only chip I had equilavent to the 74S04. Unfortunately, the computer stopped starting up the way it did before, all indicator lights come on and nothing seems to "reset" so I think I screwed up the clock signal, though it looks exactly the same on the oscilloscope (100mV pp).
Any ideas or what did I do wrong?
