Tektronix 11A71 amplifier teardown and 'easter egg' - Page 1
Forum section: electronics / general

author: tekfan
author_rank: Frequent Contributor
timestamp: May 20, 2012, 08:55:24 pm
content: Several years ago I bought a Tektronix DSA602A digitizing signal analyzer with plugins. It is a very interesting piece of test equipment but what caught my eye are the plugins it came with. Particularly the 11A71 plugin.There seems to be quite a lack of pictures of the Tek 11000 series scopes so I hope these pictures will be interesting to someone.The plugins are exactly the same size as the Tek 7000 series, but can not be physically pushed into the connector.Although 7000 series plugins can easily be converted to fit 11000 series mainframes.Right side of the 11A71 plugin. This board is all analog.Here the loop of cable can be seen which acts as a delay line to compensate for skew between various amplifiers.It connects to the input attenuator.Closeup of the input attenuator. The thick film resistors can be seen. All are laser trimmed. There is also a capacitor which is switched in when AC coupling is selected. The signal path is 50 ohm.The attenuated signal then connects to the first hybrid IC (the brown one) which serves as input protection. The signal is then converted from single ended to differential by the first white IC and then the various gain and compensation stages follow. The signal path is entirely differential up to the AD converter in the mainframe.Various compensation trimpotsCloseup of the HF design used back in the late 80'sOn the left side of the plugin is the digital section that communicates with the mainframeVery retro design. I just hope the battery in the Dallas non volatile RAM doesn't run out any time soon.Closeup of the daughter board. Looks like standard 7400 series logic and TL074 quad opamps.Now for some fun:I sat down and stared for several minutes at the plugin and the specs labeled on the frontThen I realizedLooking closely at the hybrid ICsI don't know if this is a real easter egg or not but I find it funny nonetheless.

author: muvideo
author_rank: Frequent Contributor
timestamp: May 20, 2012, 09:28:39 pm
content: Interesting pics, it's very interesting to stare at high speedanalogue designs, do you have also the probes?With suitable probes that plugin should give 1GHz BW,if I undertand correctly.Just this evening for fun I improvised an avalanche transistorpulser as per Jim William appnote (AN47 linear), it waseasy and it seem to work, but now I need a 7A29Seem that Tektronix was full of surprises back then.I wouldnt be surpised if tek actually was aware of the errorand keep the wrong layout of the panel, it's funny after all.When I downloaded the 7A26 manual I started readingit, trying to understand the inner working priciples, andthen I found that cartoon in the schematic...Fabio.

author: nctnico
author_rank: Super Contributor
timestamp: May 20, 2012, 09:34:42 pm
content: Regarding the Dallas non-volatile ram: its a good idea to make a backup. Tek has a habbit of storing calibration information in them which cannot be restored without special calibration software. I have made backups of my TDS5xx TDS7xx scopes.

author: amyk
author_rank: Super Contributor
timestamp: May 21, 2012, 07:49:49 am
content: Quote from: nctnico on May 20, 2012, 09:34:42 pmI agree, given the date code of 1986 and the expected lifetime of 10 years. You can also replace it with a pin-compatible NvSRAM and never worry about the battery again --- I think Cypress makes some.

author: Raff
author_rank: Regular Contributor
timestamp: June 01, 2012, 12:09:32 am
content: Years back I pulled apart one of those Dallas chips, it was in an old PC motherboard. I was surprised to find a lithium coin cell inside and a standard looking SRAM chip as well. Maybe yours is similar, the top just unclipped from the chip I was playing with.Regards,Raff.

author: tekfan
author_rank: Frequent Contributor
timestamp: June 03, 2012, 04:29:41 pm
content: Quote from: Raff on June 01, 2012, 12:09:32 amYes, believe it's just a standard SRAM chip but molded together with a coin cell battery. I've seen people grind away the top to get to the battery and replace it.