Tek 571 Curve Tracer repair - Page 1
Forum section: electronics / repair

author: JHuston
author_rank: Newbie
timestamp: August 29, 2024, 10:06:29 pm
content: I purchased a Tektronix 571 curve tracer off Ebay awhile back. It was listed as working but it actually did not. The current drive was out so I would see the voltage rise when testing components but no current. I finally got around to fixing that part of the unit. I tested a DUT with it and all was good. The monitor that was in the unit (a 9" CRT monochrome green) had issues at the very top of the tube and had burn in artifacts as well. After getting the unit working I wanted to swap the monitor with another unit I had. I discharged the tube's anode using a screwdriver against chassis. Installed new CRT and now I am only seeing green lines horizontally filling the screen?What did I do??This curve tracer uses 8032 Intel processor and a NS405 chip that does the video.There is 2 EEproms that store firmware for the curve tracer function and 1 for NS405 video. I read the BINs and compared to the other unit I have and they were identical. I can not figure out what the heck is going on. The service manual discusses connecting the unit to a Centronics j625 port IEEE 1284 port I believe? That's to use a VT100 terminal. I have ordered a IEEE 1284/centronics cable to USB with the plans to see if I can use my PC and emulate a terminal as thr service manual states. This is supposedly how I can see if the issue is monitor or program issue. This is over my head and any guesses would be a HUGE help. I was SO happy when it worked and was fixed then SO bummed when monitor did this and nothing else. I swapped out the monitor driver board AND the main PCB from curve tracer and it was doing the same thing?Where are all the extremely smart individuals around here?Thanks in advance.BTW- firmware that was downloaded from Tek wiki website for the 571 is different than what my unit has. I have ordered UV programmable 27C256 eeproms so that I could write their firmware versions and try it. Testing the firmware was my thought and could be the absolute wrong way to go. I was just thinking when I discharged the crt maybe it did something to cmos.

author: JHuston
author_rank: Newbie
timestamp: August 30, 2024, 01:01:58 am
content: Picture of what's on the screen.Also- I believe yesterday I could adjust the screen height to fill the entire screen. Today I am not able to. This is maxed adjustment. I will have to look at schematics and see what drives the height. If anyone knows about either issue or has questions please post I will answer.Thank you

author: picburner
author_rank: Frequent Contributor
timestamp: August 30, 2024, 07:03:06 am
content: Try temporarily putting the old CRT back in.If it has the same anomaly then something has happened to the instrument.If the problem does not occur then the new CRT is either electrically different or faulty.

author: JHuston
author_rank: Newbie
timestamp: August 30, 2024, 06:10:41 pm
content: Thank you for replying! I actually did replace the crt with the old unit to see of something has occurred to the new crt. I get the same issue regardless of the monitor and oddly enough I have the same issue with 2 different main boards which have the Intel 8032 and NS405 ICs. I am stumped where to start? I am working on a solution to connect to the ttl composite out that this curve tracer has inside the unit. This is a secondary video output so i can verify if it's monitor issue or hardware/firmware. I need to find more time to dig into this. Curious if the vertical pcb that was in during both tests somehow provides voltage for something that went out. Only way I can explain it?Any Tek wizards out there? I know theres lots od you out there WAY smarter than me that could help.

author: JHuston
author_rank: Newbie
timestamp: August 30, 2024, 06:11:37 pm
content: Also- the new and old CRTs both worked prior.

author: JHuston
author_rank: Newbie
timestamp: August 31, 2024, 01:50:05 pm
content: Anyone? Someone out there knows this stuff?

author: squadchannel
author_rank: Frequent Contributor
timestamp: August 31, 2024, 02:17:34 pm
content: You should ask in the more professional groups.io “TekScopes” group.https://groups.io/g/TekScopes