Tektronix TDS820 - Page 1
Forum section: electronics / testgear

author: eurofox
author_rank: Unknown
timestamp: May 21, 2014, 11:38:44 am
content: I have questions related to this oscilloscope.1/ What is in the NVRAM, option or/and calibration data (I try to find on Tek yahoo, Tek forum and din't find a real answer).2/ I'm not afraid to replace the NVRAM, I did it already in another equipment but all data is usually gone (battery almost dead and temperature kill it or any other reason)There should be a trick to read it by using the OS and GPIB or RS232 and some code, is just a loop from start to end address of the NVRAM and write in a file in HEX format. Maybe someone did it already for the TDS scopes?3/ Since the base of this scope I suppose is the same of the TDS540, all caps should be replaced to avoid leaking, maybe someone could advice me the exact type to order (I think there are 2 different types).Thanks in advance for sharing your experienceeurofox

author: iDevice
author_rank: Regular Contributor
timestamp: May 22, 2014, 08:50:11 pm
content: Scored on Tweedehands lately ?

author: eurofox
author_rank: Unknown
timestamp: May 24, 2014, 08:24:03 am
content: I just ask people to share possible experienceI have a TDS820 in perfect condition and would like to keep it in this condition including calibrationI have a s well a DS800 11Ghz sampling scope arriving in customsToys for "time nuts"eurofox

author: nctnico
author_rank: Super Contributor
timestamp: May 24, 2014, 09:55:51 am
content: I do the following:I unsolder the NVRAM and solder it into a DIP socket with turned pins. Next I solder a DIP socket with turned pins into the CPU board of the scope. Before placing the NVRAM back I make a copy of it with a cheap Chinese EPROM programmer. Soldering the NVRAM into a socket with turned pins is very important because you can't place an unsoldered device in a socket directly.

author: eurofox
author_rank: Unknown
timestamp: May 24, 2014, 11:05:16 am
content: Quote from: nctnico on May 24, 2014, 09:55:51 amI agree with the procedure, the only problem that I got with another instrument removing the NVRAM and according many link on the net, the data is corrupted during removing the NVRAM.My TDS820 is in good cosmetic and technical condition, I check all calibration and is completely OK, it should be a real pity to brick it but time is tickingI will break the calibration seals and open it to check the date code of the NVRAM and probably change the capacitors.eurofox

author: nctnico
author_rank: Super Contributor
timestamp: May 24, 2014, 12:59:57 pm
content: I have socketed and backed-up several NVRAMs and never had problems with losing data. I'm using a desoldoring iron with vacuum pump though. Maybe desoldering braid shorts the wrong pins.

author: eurofox
author_rank: Unknown
timestamp: May 24, 2014, 09:56:39 pm
content: Quote from: nctnico on May 24, 2014, 12:59:57 pmI did only one and it could be that the data was already corrupted, the other negative information is coming from the net.I appreciate that you provide success, this give me confidence do do it, I already order new NVRAM (1245 instead of 1645 since it is not available anymore but is normally the replacement part).I use a desoldering iron as well to remove components not the desoldering braid.I check the PCB's and there is not visible trace of leaking from the caps, I check with light from different angle.There is very little dust in the instrument and I suppose that this instrument spend most of the time on a shelf, there is unfortunately no time and power up counter available to confirm this.eurofox

author: nctnico
author_rank: Super Contributor
timestamp: May 25, 2014, 12:19:10 am
content: I left the original NVRAMs in my scopes after making a backup. Leaking capacitors can be seen if you keep the board at different angles in the light. You'll see a -more or less- circular greasy spot around them at a certain angle. The scopes I still have are from around 1995. The capacitors in those still don't leak. I only found leaking capacitors in scopes from around 1990 which leads me to believe only the early models had the problem with the capacitors. If the capacitors don't leak and the scope is from 1994 or later I'd let them be. Replacing the capacitors is a lot of work and it is easy to damage the pads.

author: eurofox
author_rank: Unknown
timestamp: May 25, 2014, 05:48:47 am
content: There is an EPROM dated 1993, the firmware is the latest that was supplied on this instrument.The NVRAM : DS1645Y-120, 9515H 059562 (I suppose the date code is week 5 year 95)The instrument front panel is protected by the classic Tek blue plastic cover and the is in mint condition.Math option is installed but I wonder why to have this on such a scope (making FFT on pulses)Timing resolution : 0.4 ps

author: nctnico
author_rank: Super Contributor
timestamp: May 25, 2014, 09:36:39 am
content: If it came with the 'vomit tray' then someone took really good care of it. I have been looking at getting a TDS820 cheap but never got that lucky. I don't want to spend too much money on such a scope because they only trigger to 2 GHz. FFT is a very nice option for checking harmonic distortion in RF amps. And you have some sort of spectrum analyser in one.

author: eurofox
author_rank: Unknown
timestamp: May 25, 2014, 09:51:32 am
content: Quote from: nctnico on May 25, 2014, 09:36:39 amI have a spectrum analyzerI have the feeling that it is not really an RF scope, is more specialized to analyse short pulses, that was the reason why I wonder the need of the math function.The one I got is ok for the calibration and based on the service manual you can calibrate it yourself without special software.It is an interesting instrument to have, is a pity that it is big and noisyI was lucky to get this one locally for a good price and I could test it before deciding to buy it. On eBay US it is 3-4 K$ to have a working one.eurofox