Tektronix 2236 repair and adjustment - Page 1
Forum section: electronics / testgear

author: velik_kazakov
author_rank: Regular Contributor
timestamp: August 30, 2017, 07:41:57 am
content: I decide to write this topic, because maybe will be interesting for someone. This repair is not like 80% of the 2236 problems - Power Supply. This scope come to me from a lot of 2236 and have no trace on Ch.1. All other was OK. Start to check the scope and find that the vertical preamp and output amplifier are ok and the problem is in the attenuators PCB (Schematic 1 in the SM). The output of ch1 always have DC component and the trace are out of the screen. Start to looking for the bad component and find that the opamp of channel 1 was dead. The output always have -8.6V. It is CA3041 and I find new one for ~1USD and exchange it. All come and now have good trace for both channels.When exchange the opamp I clean good the attenuator switches because have some trouble with it when I check the scope. After repair I exchange all caps in the PS and power distribution in the scope (do this with all 2236 that I repair).When all is done with the scope and it stay power on for 8+ hours I adjust it following the SM (I don't say calibrate, because I do not have ISO traceable lab. But I'm sure that after adjustment with the items that I have in my desk, this unit will pass calibration). Do this maybe for 3 or 4 hours.Because now find a time to adjust CTM. I was surprised from the good work of it. Measuring of the DC and AC direct from ch1 are good for all ranges after adjustment.Now it is ready for new live.

author: dave_k
author_rank: Frequent Contributor
timestamp: August 30, 2017, 08:02:56 am
content: Nice work! Another Tek lives on...

author: velik_kazakov
author_rank: Regular Contributor
timestamp: August 30, 2017, 08:48:31 am
content: Quote from: dave_k on August 30, 2017, 08:02:56 amAnd some other wait to find a time for repair.

author: carl_lab
author_rank: Frequent Contributor
timestamp: August 30, 2017, 10:21:55 am
content: Nice collection!

author: velik_kazakov
author_rank: Regular Contributor
timestamp: September 01, 2017, 04:50:22 pm
content: Something else for this scope. After assemble all I power one the scope for all day (do this with all after some repairs). After 3-4 hours the focus going bad. The focus was turned full ccw and the focus was still bad. Open it and check some resistors (in yellow in the schematic) and find 2 was not in good condition. After replace 2 of 4 all come back OK with good spot - do this in XY and adjust with focus and astigmatism for best small dot and after this check the trace.

author: wasyoungonce
author_rank: Frequent Contributor
timestamp: September 01, 2017, 08:37:03 pm
content: VeligerI have a 2236 and need to do the PSU and focus resistors. Do you have a list of PSU capacitors. I was doing this but got side tracked. Any info appreciated as alternates are required. I really need to pull it apart to measure he capacitor sizes then order them, so any info will speed this up.I also noted focus drift after some "on time", I've looked up the schematics for these, just need to order.Keep up the good work,Brendan

author: velik_kazakov
author_rank: Regular Contributor
timestamp: September 02, 2017, 07:03:53 pm
content: Quote from: wasyoungonce on September 01, 2017, 08:37:03 pmSure, but I'm not sure that you will understand what I write (look in the picture). To be outspoken, I can't too after 3-4 months when write this to order caps for 10pcs 2236. So, let to write this list:First (for safety - lookhere. It is the same rifa 2200p) c902, c903 - 2.2n/250V Y cap on the filter pcb.c904 - 2.2n/250V X cap (I install 400v - this can gete here) - A1 board to the power switch.on A1 boardC906 - 100uF/400-450VC925 - 100uF/50VC940 - 1000UF/63VC943,C942 - 10UF/100-200VC944 - 1UF/50V tant.C954 - 33UF/200+V (I put 47/400V)C956 - 330UF/63V ( in SN <B022267 IT IS 4700UF/10V, but I always install 330uF)C960,961,962,963,968, - 1000UF/35V (here need to be 6pcs, but can't find what missing - order 6 and replace all 840uF with 1000uF)C970 - 4700UF/25Vthis was on PS, but if you want, can to replace some other caps in power distribution in the scope. I do this when recap the scope.A2 (attenuator board) - I put our this board for cleaning of the input switches and when the PCB is out replace this caps. In some scopes here have 2 elect. and 2 tantalum caps but I always install C90, C91, C93, C96 - all with 22uF/35+V.A12 multimeter input board - c1903,c 1904 - 100uf/35vsome - 22uf/25+v - all in power distribution (maybe 4-5ocs)100uf/25+v, 10uf/25+v, 47uf/25+v all axial - on CTM boardthis is all that I remember for Power supply and power distribution on 2236. Maybe forget someone, but most important is here.About focus - always have bad resistors (510k/0.6W) in the scopes that I check. You can to order 10pcs and if need to exchange some after checking.If need more info for 2236, maybe can to help with something.

author: David Hess
author_rank: Super Contributor
timestamp: September 03, 2017, 02:04:42 am
content: I am jealous. I fixed all of my 22xx oscilloscopes and now they just work.

author: wasyoungonce
author_rank: Frequent Contributor
timestamp: September 03, 2017, 03:41:02 am
content: Thanks velikI'm in hospital at the moment so are not able to pull mine apart just yet. I was just about to then I needed spinal fusion. I'll be ok and try to get back to doing the caps and focus resistors in around a month, when I'm better.I'll post back then but many thanks this saves me a lot of leg workBrendan

author: velik_kazakov
author_rank: Regular Contributor
timestamp: September 03, 2017, 07:12:55 pm
content: Quote from: David Hess on September 03, 2017, 02:04:42 amMy first repair of 2236 cost me lots of time and lots of blowed components. All in power supplyand because I do all fast and w/o to read service manual word by word. Think that will do all for some minutes and all will be ok, but just goind bad and bad. Now work 3 days on 2236 and still not fixed. But will continue until do it.Quote from: wasyoungonce on September 03, 2017, 03:41:02 amHope you will be ok in short time.

author: buck converter
author_rank: Regular Contributor
timestamp: September 03, 2017, 07:40:13 pm
content: I have 2235, which is just a 2236 minus the DMM. The horizontal sweep sometimes ripples in the wrong direction, do you know what could be wrong?https://www.eevblog.com/forum/repair/tektronix-2235-horizontal-problem/

author: velik_kazakov
author_rank: Regular Contributor
timestamp: September 03, 2017, 08:16:19 pm
content: Quote from: buck converter on September 03, 2017, 07:40:13 pmYou write that you have a second scope. Do you check all power supply outputs for ripples on it?Tomorrow will check something and will write back. Want to try something befor to write it here. I'm not sure.

author: don.r
author_rank: Frequent Contributor
timestamp: September 03, 2017, 09:12:55 pm
content: The power indicator LED has gone on my 2225 and I can't believe I have to disassemble just about everything to get into the front panel.I may just attempt to replace it from underneath with the panel and front board in place.EDIT: Not as bad as I thought. Analog boards on these are too bad to remove.