TDS724D 7 segment diagnostic display - meaning? - Page 1
Forum section: electronics / repair

author: tkamiya
author_rank: Super Contributor
timestamp: September 19, 2020, 02:20:15 am
content: I have just acquired a non functioning TDS724D, a Tektronix scope.First off, when powered on, all LED on front panel lights but nothing on display. (This is a CRT, not LCD although it looks like a LCD unit) Fan works and there is a faint one "click" on floppy drive. Visually, I don't see any burned parts or exploded/leaked caps. There is a 7 segment diagnostic display on CPU board. It goes through iterations but gets stuck at top and bottom segment alternatively flashing. I went through a service manual but there is no mention of what this means.I have not tested the power supply, but I'm curious as to if anyone has a chart on the above mentioned 7 segment display.Anyone?ps. There are several threads on these units and they mention "diagnostic port". Apparently, a special jig is required to connect to this port and then to RS232C. But link on the actual document on this jig is all broken.

author: madao
author_rank: Frequent Contributor
timestamp: September 19, 2020, 04:56:19 am
content: two segment lights up alternating -> firmware is good, someone of hardware is failed, you need debug interface-Adapter7-Seg Displays meaning is only worth in bootloader-mode.Here two file, which i have saved from dead theard/link since time ago.Gerber file (debug-interface.zip) , it is mine design (has little fault, you must put him 180° to CPU board. )

author: tkamiya
author_rank: Super Contributor
timestamp: September 19, 2020, 05:32:49 am
content: Thank you for sharing!I'm sorry, I am having trouble understanding what you are telling me. I read the serial interface port and debug port does not share the same connection. So a special adapter has to be made. I think that is what your first two pictures are showing. The 20 pin edge card connector is the debug port we are interested in, correct?But I was not aware I needed a micro controller. What does your board do? I see isolaters, then I see it goes to TDS-TX and TDS-RX as well as flow control. Or is this showing part of the scope hardware? I'm sorry, I'm totally lost here.

author: madao
author_rank: Frequent Contributor
timestamp: September 19, 2020, 06:09:58 am
content: Yes, 20 pin edge connector on CPU is debug / console interface.You put this interface on CPU board and computer. It make log while boot up. You can see, at which point are DSO hang up .Terminal setting , i believe 9600 baud, no flow control need.Schematic, it is not mine, it is saved from dead theard. Most interessing parts is only 20 pin connector and 68681 UART Controller.Here a picture of screenshot of result, (a TDS754C doesn't start up complete)

author: keystone
author_rank: Contributor
timestamp: September 19, 2020, 06:20:34 am
content: Where can you get one of those premade boards?

author: madao
author_rank: Frequent Contributor
timestamp: September 19, 2020, 06:25:50 am
content: gerber files in ZIP-file is attached on my first answers on you. You can made it by jlcpcb (eevblog's advertisment), 5 pieces cost only 2 $, Quality good.I can sending pcb with part to you, but you must paid over $30 for only shipping , german post.

author: Jwalling
author_rank: Unknown
timestamp: September 19, 2020, 08:35:34 am
content: Quote from: keystone on September 19, 2020, 06:20:34 amHave a look here:https://www.eevblog.com/forum/testgear/console-port-debug-adapter-for-tek-tds500-tds600-and-tds700-series-scopes/Much simpler solution...

author: tkamiya
author_rank: Super Contributor
timestamp: September 19, 2020, 12:37:20 pm
content: Ah, I understand now. The Motorola chip is UART! I thought it was a cpu chip.I also understand optional serial port already contains UART.... so it is possible to make an adapter for it.I kind of prefer an independent solution, as I may have to use it for more than one machine which may or may not have the serial option. These scopes are getting cheaply available now.

author: tkamiya
author_rank: Super Contributor
timestamp: September 19, 2020, 05:25:53 pm
content: I'm seeing 68681 UART chip is no longer in production. Digikey shows zero stock, Mouser does not even show one, and of course plentiful on eBay. I should have kept those "serial adapter card' from 80s.... About 40 years too late.

author: madao
author_rank: Frequent Contributor
timestamp: September 19, 2020, 07:43:08 pm
content: 68681, i have buying two from china, it look like orginal. (new, no "used" with grinded surface ) and it works. Of coruse, i am careful by semicondutor from china.Greetingsmatt

author: tkamiya
author_rank: Super Contributor
timestamp: September 19, 2020, 07:56:33 pm
content: Greetings....Yes, I'm sure there are many genuine chips coming from China. But it is also true some people do anything knowingly for money. Fakes, factory seconds, used pulls, etc, etc, etc. Unless necessary, I stopped buying semi-conductors from eBay. It's just not worth the hassle. Especially things that matter, I try to stick with known vendors. Pay a bit more but I can be assured I get the right product.

author: madao
author_rank: Frequent Contributor
timestamp: September 19, 2020, 08:01:46 pm
content: honestly, i want sending you a complete board. Wait.. i look on DHL site... yes i can ship him now for less than $30Now, i can ship to you with 9€ (~$10.5 ) ship cost and price for complete PCB, checked. Can you wait over one months (sea shipping) ?Greetingsmatt

author: ChuckDarwin
author_rank: Regular Contributor
timestamp: September 19, 2020, 09:20:48 pm
content: MaxLinear XR68C681 (Mouser US) viable alternative? Or Philips SCC68681/SCN68681 (just saw that the SCN68681 is already noted in the schematic)

author: tkamiya
author_rank: Super Contributor
timestamp: September 19, 2020, 10:00:26 pm
content: If cost makes sense, I'd prefer that, too. Can you work out a price and let me know via PM?Quote from: madao on September 19, 2020, 08:01:46 pm

author: madao
author_rank: Frequent Contributor
timestamp: September 20, 2020, 03:40:18 am
content: Quote from: ChuckDarwin on September 19, 2020, 09:20:48 pmYes, SCN68681 fit here, but also osbolent since long time agoXR68C681, i have checked datasheet, yes it may fit !GreetingsMatt@tkamiya , offer is for you, i have sent a pm to you.

author: tkamiya
author_rank: Super Contributor
timestamp: September 20, 2020, 04:50:52 am
content: PM replied. YES!

author: keystone
author_rank: Contributor
timestamp: September 20, 2020, 06:23:04 am
content: Quote from: madao on September 19, 2020, 08:01:46 pmI would be interested in a board also. Please PM me. Thank you.

author: madao
author_rank: Frequent Contributor
timestamp: September 20, 2020, 06:35:21 am
content: I have only few complete board, my offer is for him.But you can use gerber file from my first answers, or you want complete , checked board ?All information:https://www.eevblog.com/forum/repair/tektronix-tds500-700-debug-konscole-interface/GreetingsmattImportant: Pleas delete old gerber file (with file date 13.02.2020 ) and use gerber file with newer file date 30.05.2020.First answer is edited and old gerber file is already replaced.Sorry !!

author: keystone
author_rank: Contributor
timestamp: September 21, 2020, 06:53:52 am
content: I want a complete checked board. Thank you.

author: coromonadalix
author_rank: Super Contributor
timestamp: September 21, 2020, 10:23:02 am
content: @keystone you have to make the board .... read the previous post before yours ....