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Tektronix 4052 Troubleshooting

daver2 said:
Cheers Monty. All will come to those who wait!

I have seen a sketch of the 4052A MAS in one of the Tek documents - and your schematic confirmed what I thought regarding the removal of the FPLAs and patch ROMs - although it did throw up the interesting item that the 'extra' EPROM lives from 0000 - 3FFF (I wondered how the extra EPROM appeared in the memory map. Now I know)!

Looks like J419 just completely disables the on-board ROM to me (so not as interesting as I had first guessed).

Dave
Click to expand...

Dave,

I realize that the schematics from Roland for the MAS are all the 4052A diagrams - here is my link to scans I just made of the 4052 MAS diagrams 1 through 5:

Tektronix 4052 MAS schematics 4-1 to 4-5

Monty
 
My Tektronix 4052 is now working again!

My Tektronix 4052 is now working again!

I fixed my Tektronix 4052 computer display issues today!

I replaced the U184 op amp 5558 with an MC1458.

Here is a photo of the section of the display board with the replaced op amp highlighted in yellow.

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First program I loaded to do more testing was my Battlestar Galactica "Vipers on Patrol":

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Then I copied my port of Colossal16 Adventure in BASIC to tape to try:

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I plan to attend the VCF PNW in Seattle on March 21 and 22, and will be bringing my 4054A and repaired 4052.

I plan to put the 4052 for sale on the consignment table - unless it is sold prior to the VCF Festival in Seattle.

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tingo said:
Nice! It is a good feeling when you manage to fix something that broke.
Click to expand...

Thanks, Torfinn!

I have really enjoyed reliving my fond experiences with the Tektronix 4051 computer from the 1970's - and want at least one other person to be able to do the same with my 4052 computer.

The 4052 and 4054 computers have the huge 7-10x performance advantage over the 800MHz 6800 based 4051, due to the custom 25MHz AMD2901 bit-slice 16-bit architecture, which not only emulated the 6800 8-bit instructions, but added sixteen 16-bit CPU registers, 64-bit floating point instructions, and 16-bit address and data in 1979, while still providing the state of the art 1024x780 vector graphics (4096x3072 for the 4054/4054A)!

Monty
 
I had an experience with a failed -20V rail on the Display board of my 4052, the culprit was apparently a vias from the top to bottom layer of the PCB had failed and disconnected -20V from the XY deflection amplifiers. I've seen failed vias in 70s-80s car radios exposed to hot temperatures, but this is the first time I've seen a failed vias on a computer. But this computer was stored in a non-climate controlled Texas garage for a number of years before I had acquired it so I suspect the hot/cold temperature cycling may have weakened this vias connection.

The high level failure symptom I saw on the display was a dot in the center of the screen on power up. I noticed if you hit any character key repeatedly then suddenly the characters would start appearing but only as flat lines past the center point, and if you hit the Return key repeatedly to position the cursor to the lower right quadrant then the characters and cursor would appear on the screen normally. It looks like this: https://electronixandmore.com/resources/teksystem/tek_display_neg20v_failure.jpg

Digging into the display board, I measured the I/O board producing X and Y deflection voltages in the range of approx +/-8V. The lower right quadrant of the display correspond to X and Y voltages that are below 0V (e.g. top half is Y>0V, left half is X>0). I traced the XY voltages from the I/O board through the amplifiers and noticed the final output stage that is powered by the unregulated +/-20V died when deflecting below 0V indicating a -20V rail failure. Also there is a 5.1V zener regulator off -20V to provide a ~-15V bias that was measuring +10V with respect to ground. What was puzzling to me at first was I had measured -20V as expected at the connector pin 8 of J54 on the display board. All the other power supply voltages at this connector even checked out OK. It wasn't until I measured the zener voltage that I realized -20V was not making it to the rest of the board and found a disconnection at the vias where the trace transitioned to the other side of the board. The fix was simply soldering in a jumper wire from the vias to a -20V point in the deflection circuitry, like this:
https://electronixandmore.com/resources/teksystem/tek_display_neg20v_failure_fix.jpg

It's one thing to see failed components, but a failed PCB trace... :eek:
 
(mentioning just for fun) I had a Tek 4006 terminal start to fail at X deflection shortly before I was scheduled to exhibit it. I troubleshooted the problem down to a culprit op-amp but didn't really want the time or the trouble of extracting the its circuit board to get at the solder side (if you know the way it's fitted, you may sympathise)... So I clipped the legs and grafted a socket onto the stumps, then put the replacement op-amp into the socket. Worked just fine and is still like this today:

photos.app.goo.gl

New photo · Tuesday, Oct 31, 2023 📸

Tap to view!
photos.app.goo.gl photos.app.goo.gl
 
jbstan said:
I had an experience with a failed -20V rail on the Display board of my 4052, the culprit was apparently a vias from the top to bottom layer of the PCB had failed and disconnected -20V from the XY deflection amplifiers. I've seen failed vias in 70s-80s car radios exposed to hot temperatures, but this is the first time I've seen a failed vias on a computer. But this computer was stored in a non-climate controlled Texas garage for a number of years before I had acquired it so I suspect the hot/cold temperature cycling may have weakened this vias connection.

The high level failure symptom I saw on the display was a dot in the center of the screen on power up. I noticed if you hit any character key repeatedly then suddenly the characters would start appearing but only as flat lines past the center point, and if you hit the Return key repeatedly to position the cursor to the lower right quadrant then the characters and cursor would appear on the screen normally. It looks like this: https://electronixandmore.com/resources/teksystem/tek_display_neg20v_failure.jpg

Digging into the display board, I measured the I/O board producing X and Y deflection voltages in the range of approx +/-8V. The lower right quadrant of the display correspond to X and Y voltages that are below 0V (e.g. top half is Y>0V, left half is X>0). I traced the XY voltages from the I/O board through the amplifiers and noticed the final output stage that is powered by the unregulated +/-20V died when deflecting below 0V indicating a -20V rail failure. Also there is a 5.1V zener regulator off -20V to provide a ~-15V bias that was measuring +10V with respect to ground. What was puzzling to me at first was I had measured -20V as expected at the connector pin 8 of J54 on the display board. All the other power supply voltages at this connector even checked out OK. It wasn't until I measured the zener voltage that I realized -20V was not making it to the rest of the board and found a disconnection at the vias where the trace transitioned to the other side of the board. The fix was simply soldering in a jumper wire from the vias to a -20V point in the deflection circuitry, like this:
https://electronixandmore.com/resources/teksystem/tek_display_neg20v_failure_fix.jpg

It's one thing to see failed components, but a failed PCB trace... :eek:
Click to expand...
Congratulations for your 4052 repair! 🥂

Do you have a 4052R12 Graphics Enhancement (Fast Graphics) ROM Pack or @jdreesen's 4052 Multifunction ROM Pack (which should include the R12 ROM among several others)?

Most of my latest 4050 BASIC programs require the R12 ROM Pack.
 
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