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Philcogrump
January 19th, 2005, 04:51 AM
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?

bobar
July 21st, 2005, 09:48 PM
Possibly something is holding the clock line low (or a very heavy load). I too believe you should be getting about 3 volts p-p for the clock. I have a 4052 that's not working at all. Is is possible to get a copy of the schematics?

Bob

MystikShadows
July 22nd, 2005, 03:57 AM
Is this the machine you're talking about?

http://www.electronixandmore.com/misc/computers/2tek4052.jpg

Looked mighty good considering it came from 1977 :-)

Philcogrump
December 30th, 2005, 10:58 PM
MystikShadows, yes, this is a picture of my first 4052. Believe it or not, it sat outside for a few days when the previous owner was cleaning out the garage.

I acquired a second 4052 from the same guy who gave me the first one and using parts from the two, I found that the I/O board on the first one was bad, hence the dot in the middle of the screen. The second one seemed to have everything working (and the previous owner said it worked last time he turned it on 20+ years ago), but it booted up sporadically, then I tried swapping MAS (memory board) boards between the two and got a cursor at last, but the BASIC interpreter was nonfunctional. Fortunately, the guy had two sets (array of 8) of ROMs with BASIC in them, and after replacing the ROMs on the MAS board in a variety of methods, I finally got the second 4052 fully functional except I left out the expansion ROMs which probably were only intended to be benefital for certain software that I do not have.

This is the end of the thread for hardware problems with the 4052. I'll make a separate thread about programming and using the 4052.