[SOLVED]Tek TDS744A slow refresh or recovery - Page 1
Forum section: electronics / repair

author: Daxxin
author_rank: Regular Contributor
timestamp: February 14, 2018, 07:21:24 pm
content: applyng signal or changing channel very very slow to refresh even with the input disconnected remai sine trace on the screen to refresh need tochange trigger channel or rotare h or v , look like something wrong with video ram, sometime slow but recover sometime not like ch3 in the video.-never own scope like this before but i guess its not regular.look at the video.https://youtu.be/QaDCtnPcZgU

author: Jwalling
author_rank: Unknown
timestamp: February 15, 2018, 10:45:00 am
content: I suspect it's because you are using ET sampling *and* averaging. Save the setup and post it here and I'll try it on a TDS784A.

author: Daxxin
author_rank: Regular Contributor
timestamp: February 15, 2018, 06:21:20 pm
content: Quote from: Jwalling on February 15, 2018, 10:45:00 amHi Jwalling , here the setup i will try to different set , here setup attached

author: Jwalling
author_rank: Unknown
timestamp: February 16, 2018, 12:35:52 pm
content: The only difference I noted is that when I inputted the signal to CH3, then set the trigger to CH3 (From CH1) the signal resolved quickly, where yours seems to sort of fade in but never looks very good. Have you run the full self test from the utility menu as well as SPC?

author: Daxxin
author_rank: Regular Contributor
timestamp: February 16, 2018, 06:23:12 pm
content: Your right i get processor error with the test with following gpib logERROR: diagnostic test failure, dsp68kD1MemTest, ** addr = 0x720a680 exp data = 0x5555 actual = 0xff55, ** addr = 0x720a682 exp data = 0x5555 actual = 0xff55, ** addr = 0x720a684 exp data = 0x5555 actual = 0xff55, ** addr = 0x720a686 exp data = 0x5555 actual = 0xfd55, ** addr = 0x720a688 exp data = 0x5555 actual = 0xff55, ** addr = 0x720a68a exp data = 0x5555 actual = 0xff55, ** addr = 0x720a68c exp data = 0x5555 actual = 0xfd55, ** addr = 0x720a68e exp data = 0x5555 actual = 0xfd55"

author: Jwalling
author_rank: Unknown
timestamp: February 17, 2018, 11:19:16 am
content: I have a few failures in my logs that may be of some use. These were pulled from the console port.U1009-17 shorted to VCC:dsp68kMemTest .................. ***FAIL***..error details:ERRORID: 153 diagnostic test failure dsp68kD1MemTest** addr = 0x7200000 exp data = 0xf7ff actual = 0xffffandU1009-17 SRAM open etch:dsp68kMemTest .................. ***FAIL***..error details:ERRORID: 153 diagnostic test failure dsp68kD1MemTest** addr = 0x7200000 exp data = 0xf7ff actual = 0xffffSo maybe that memory chip or associated circuitry. U1008 may also be suspect.

author: Daxxin
author_rank: Regular Contributor
timestamp: February 18, 2018, 11:35:16 am
content: thanks for sharing the info , its ok to replace with AS6C1008-55SIN?i seen have 2 additional not populated sram expansion U2008 and U2009 , theres benefits to install also them?

author: Jwalling
author_rank: Unknown
timestamp: February 18, 2018, 12:17:58 pm
content: Quote from: Daxxin on February 18, 2018, 11:35:16 amThat seems like a suitable replacement, but I'm not saying that one of the chips is defective. It could be some other device that's associated with the circuit.I would not install memory where none ever existed in the first place.

author: andy2000
author_rank: Frequent Contributor
timestamp: February 18, 2018, 04:45:43 pm
content: Start by checking for broken solder connections. I had a 744A that developed some bad connections around the large memory controllers which caused memory errors.

author: Daxxin
author_rank: Regular Contributor
timestamp: February 18, 2018, 08:17:50 pm
content: i'm too late reading yours replies.. i have 2 M5M51008 but 100ns instead 70ns replaced alredy , well before the test very short (run 30 seconds without any graphical shapes tests) then i was gettingprocessor fail , now seems the test is running very long then at the end i'm getting the banner instead the result and the scope freeze stucking on the banner , do you think slower sram can cause this?by the way ordered alredy the correct sram.

author: Jwalling
author_rank: Unknown
timestamp: February 19, 2018, 11:10:47 am
content: Quote from: Daxxin on February 18, 2018, 08:17:50 pmIs switch 3 on the dip switch set on or off?

author: Daxxin
author_rank: Regular Contributor
timestamp: February 19, 2018, 06:12:25 pm
content: Quote from: Jwalling on February 19, 2018, 11:10:47 amthis the actual dip switch positions

author: Jwalling
author_rank: Unknown
timestamp: February 19, 2018, 06:31:51 pm
content: Then it sounds like something happened when you replaced the chips. Could be that the access time is too slow, or a damaged trace from the removal process.

author: Daxxin
author_rank: Regular Contributor
timestamp: February 20, 2018, 08:12:24 pm
content: Replaced with 2 new 55ns M5M51008 everything fine thanks Jwalling for the inputs was a big big help , i will post video soon, very fast now changing settings from front panel.

author: Jwalling
author_rank: Unknown
timestamp: February 21, 2018, 10:47:23 am
content: You're welcome!