Re: Is my Tek 468 beyond repair?


Hi John, there is a zip document on Bluefeather site but someone posted maybe yesterday that it was down, with all the info and bin files to programme.
I also did a compilation of all this with a conversion socket and it was on Bluefeather and maybe on Ko4bb site. I can send you both if need be. On this site in the files section there should be a 12KB file and is just the bin files. A more complete file with pinouts and data sheets is 1890KB, not sure where it is but probably Ko4bb anyway.

Below I will post some of the discussions on Tekscope that I had copied to text files and now reside in my Tek 468 folder. Losts of words of wisdom (also check our archive of previous posts) from Tekscopes member Reed Dickinson our 468 guru.


July 2017

468 Repair Tips -
From the TekScopes mailing list:

I just finished a 468 that had a bad rom.

Just for the record, there is an error in the troubleshooting section relating to the testing of just the analog section of the scope. If the processor fails, you will have a hung up trace off screen on the left side of the scope.

The troubleshooting section states to disconnect the p3008 connector on the A12 trigger board, pull the p483 connector cable and jumper the pins. Then, on the A14 vertical mode switch board move the p307 connector to the p206 test mode port.

This places the scope in analog mode and displays ch1 & 2 chopped.

The only problem is that when you disconnect the p3008 connector, you kill the +5vs source that is used on A14 - p206. The +5vs comes from the power supply on the timing board and powers all the digital logic.

The work around is to use a jumper to the +5 on the interface A15 board (test point) to pin 3, 4, or 5 on the p307 cable to force it to 5 volts, then it will work. This applies +5 to the ch 1 select, ch2 select, and /xy select, and a ground to the /chop select.

I can't tell you how much time it took to find that out. Hope this helps someone in the future.

The bad rom was one of the gold top chips.

Regards, Tom

Subject: [TekScopes] Appraisal Tek 468
Date: Sat, 7 Apr 2007

Hi Gang:

I have found that the weakest links of a 468 are the ROM's, the 8 segment switch on the top board and the microprocessor power supplies on the rear assembly. I was able to design a circuit to read the ROM's and can now program a 27C64 with a 28 to 24 pin adapter to put these great oscilloscopes back on the air. I also wrote and programmed a ROM that reads the value of the 8 section switch and displays the value in octal on the display, most helpful for locating a problem with the data bus or a stuck level on a tri-state device. The Volume I manual has tables of check sums that will help you diagnose ills and these are indeed useful albeit a bit tiring to work with. I have also read and programmed a 27C64 for the 067-0989-XX test ROM. It uses the same 28 to 24 pin adapter as the other ROM's. If anyone needs an operational ROM or the test ROM drop me a note off line and we can discuss your problem. If you find that your 468 does not display the marching numbers on the 7 segment display during boot-up then check the 8 segment switch on the upper board. It appears to be affected by the flux used in the wave soldering operation and frequently needs replacement. I usually install a 16 pin socket in that position to accept the switch. The microprocessor power supply is a royal PITA to work on. I can offer no quick suggestions here, just use normal troubleshooting techniques. When reassembling do NOT put long screws in the two center holes of the rear bezel as they will crack the PC board in the rear and then you really will have a problem. If that happens you can send the board to me and I can repair it as I made a point-to-point wiring list. Overall the 468 is a truly magnificent instrument. It encompasses all the very best features of the 465B along with the ability to instantly change from an analog to a digital instrument. The 10 MHz digital bandpass does leave something to be desired but is satisfactory for many applications.

Reed Dickinson

Read Me text from

The Tektronix Scope, For The Most Part Is A Reliable Instrument. Its Main Weakness Is The Two Firmware ROMS (U565, And U575) Tek # 160-0459-01 And # 160-0759-01. These ICs , Of Course Are Custom Devices Made By Mostek In The Late 70s-Early 80s. As They Are No Longer Aavailable (It Seems From Anywhere), I Have Found The Latest Firmware Version (So I Am Told) . The Files Listed (2764.bmp, And 2764a.bmp) Are The Pinouts Of The Common 2764 EPROM From Intel, Which I Used For My Replacement ROMs. The File (MK36XXX) Is The Pinout For The Obsolete Tek Roms (U565, U575). The File (Fig. 1.bmp) Is The Hand Drawing Of The Adaptor To Convert A Programmed 2764 To The Mostek 36xxx Pinout. The File (OMK36693) Is The "Bin" Of The New "MK36693", Which Is "Burned" To A 2764. The Same For File (OMK36694). Most EPROM Programmers Should Do The Job. Good Luck On Your Textronix 468 Restoration!!!!

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