Tek 2235 PS Cap list/upgrade - Page 1
Forum section: electronics / repair

author: Suzook
author_rank: Contributor
timestamp: July 02, 2022, 08:44:17 pm
content: Got a mint tek 2235 that is working fine, but would like to recap the PS before it fails. Does anyone have a complete list for just the PS? Would appreciate it. Thanks

author: tautech
author_rank: Super Contributor
timestamp: July 03, 2022, 09:42:32 am
content: While you have asked several times for this with zero help lets try and guide you through to finding the info you need.As no one has stepped up lets work through how to get this info and in the case of this scope, full manuals should be available from here:http://w140.com/tekwiki/wiki/Main_PageOld Tek stuff was infamous for not only their schematics but their PCB layouts and component lists too.As for a full recap of a scope that you say is working fine I would advise against it and rather focus on circuit areas that we know are generally under some stress.They would be the PSU and and EHT PSU which for most reasonable modern instruments are likely to be SMPS which generally require better than your ordinary electrolytic cap and instead should have Low ESR versions fitted as the high frequency switching requires a low impedance cap to work at those frequencies.At one time we just shot gunned the lot however this is a field that's beneficial to understand which components are under stress and the only way to achieve this is to have instruments that can measure capacitance and ESR however these things do cost but they are also a worthy investment for your future in this hobby.There are a few options and will recommend the DR5000 whereas without a further investment in SMD tweezers as you get into all the miniaturized stuff we have these days, you can find yourself disadvantaged where instead I'd recommend you go whole hog and get SMD Smart tweezers that you can also use on most through hole components too.Here's some very well priced versions:https://www.eevblog.com/forum/testgear/design-a-new-precision-lcr-tweezers/Others prefer these:https://www.peakelec.co.uk/acatalog/jz_instruments.html(also available on Amazon)Back to your SMPS caps........Those caps in the PSU LV path (secondary) most anywhere can be considered for replacement as they will mostly be Low ESR and working under some stress along with the commonly overlooked VCC cap for the SMPS controller, normally a little chap in the range of 20-50uF and 50V rated which needs provide a reasonably clean supply to the SMPS and if it gets leaky sometimes the SMPS controller fails to kick off at power On.The EHT supply is another matter and the HOT secondary side is normally served with HV ceramic caps although the primary side reservoir caps are worthy of testing however unless specified are not normally low ESR.Come back with a schematic and list of what you think might need replacing and I'll drag some chaps here to give you marks outta 10.

author: Suzook
author_rank: Contributor
timestamp: July 03, 2022, 12:36:50 pm
content: OK, So here goes... Im a newb, so go easy...LOLC900 ,902, 903, 904, 906, 925, 940, 942, 943, 944, 954, 960, 961, 962, 963, 968, 970Now, What do I replace them with? Im seriously over my head figuring that part out.

author: David Hess
author_rank: Super Contributor
timestamp: July 03, 2022, 12:51:06 pm
content: Just to throw some gas on this fire, the 2235 was the first oscilloscope of that series and later models upgraded parts, including the power supply capacitors. If nothing else, this gives considerably leeway in selecting the values of parts, so do not look for exact replacements. I would start with diameter and lead spacing so the new parts fit.If you want something else which should be replaced, the focus resistor chain in the 2235 uses Allen-Bradley carbon composition resistors which were replaced with high voltage metal film resistors, Vishay (?) VR25 and VR35 series, in later models.

author: David Hess
author_rank: Super Contributor
timestamp: July 03, 2022, 01:00:18 pm
content: Quote from: Suzook on July 03, 2022, 12:36:50 pmThis is my list for the 2232 from when I did a survey of what Tektronix changed. It represents what was present and not modern recommended replacements; I have not gotten that far.+100 Volt Capacitors +100 Volts C954 33uF 160V +50% to -10% 33uF 160V +50% to -10%+30 Volt Capacitors +30 Volts C956 270uF 40V +100% to -10% 270uF 40V +100% to -10%DC Fan Capacitors +8.6 Volts Fan C965 4700uF 20% 10V 4700uF 20% 10V+/- 8.6 Volt Capacitors +/- 8.6 Volts C960, C961, C962, C963 840uF +100% to -10% 12V 1000uF +100% to -10% 12V+5 Volts Capacitors +5 Volts C968, C970, C958 840uF +100% to -10% 12V 1000uF +100% to -10% 12V-5 Volts Capacitors -5 Volts C964, C959 840uF +100% to -10% 12V 1000uF +100% to -10% 12VInput Capacitor Preregulator Input Capacitor C906 75uF +50-10% 450V Sprague 17D1149 270uF 20% 450V TK0900Output Capacitor Preregulator Output Capacitor C940 1000uF 20% 50V Nichicon ULB1E102TFAANA 1000uF +50-10% 50V Nichicon ULB1E102TFAANABootstrap Capacitor Regulator Controller C925 100uF 20% 25V Nichicon ULB1E101MEA 100uF 20% 25V Nichicon ULB1E101MPA

author: Suzook
author_rank: Contributor
timestamp: July 03, 2022, 01:32:42 pm
content: Here's what I have come up with. Hopefully someone can check this out please???https://www.digikey.com/short/7z78qdpn

author: floobydust
author_rank: Super Contributor
timestamp: July 06, 2022, 05:14:17 pm
content: Can you not use search? You've asked for the 2235 cap list in at least three threads! What a mess.https://www.eevblog.com/forum/testgear/recap-ps-tek-2235/https://www.eevblog.com/forum/repair/tek-2235-ps-cap-listupgrade/https://www.eevblog.com/forum/testgear/tektronix-2235-repair-thread/msg4275634/#msg4275634I'd already posted the cap list here:https://www.eevblog.com/forum/repair/tektronix-an-usm-4882235-high-8-6-v-ripple/msg2539461/#msg2539461Your Digi-Key list has different lead spacings for C925, C940

author: Suzook
author_rank: Contributor
timestamp: July 06, 2022, 08:57:18 pm
content: Obviously I cant readThanks, I guess? And half that list is out of stock. But thats life these days