Tek 213 Repair / Fitting Option 1 for 240V - Page 1
Forum section: electronics / repair

author: gareth
author_rank: Contributor
timestamp: October 09, 2014, 10:43:04 am
content: Partly inspired by Dave's teardown, I got a faulty Tektronix 213 dmm oscilloscope from ebay for my birthday. The main part of the fun is going to be fixing it, then I have to decide whether to upgrade the battery and/or fit a modification or two - there is a circuit floating around to fix the constant 6mA power draw that otherwise drains the batteries prematurely.But I'm here to ask about the factory modification to change the supply voltage from 110V AC to 240V AC - the scope is from the states so this wasn't fitted. I live in the UK so need to supply the scope with 240V.According to the parts list, C416 is only fitted with 'Option 1' - the 240V supply option. Option 1 seems to consist of only this part, no other changes to the scope or transformer seems indicated. This capacitor is listed as 'CAP.,FXD, CER DI:0.01UF,+100-0%,250V and was originally made by ERIE TECHNOLOGICAL PRODUCTS, INC Part no. 8131-250651103p.My first question is to confirm that I can just use a modern ceramic disc capacitor, and if so any advice as to the type? There are two sorts available at cpc here for example:http://cpc.farnell.com/murata/debf33a103za2b/capacitor-0-01uf-1000v/dp/CA05043andhttp://cpc.farnell.com/murata/de2f3kh103ma3b/capacitor-x12-10nf/dp/CA06011but I can't really discern the difference.I've looked at the service manual (what a joy - diagrams, schematics, a four-page flowchart of diagnostic procedures, the whole nine-yards!) and I'm still confused as to how this mod works. The schematics (attached) show the capacitor attaching to one side of the AC input line after the filter transformer. So this unrectified AC gets passed through the capacitor and then attaches to the midpoint of two output caps?I don't really understand how this circuit works in either configuration!! I think I follow the basics of regular bridge rectification and then smoothing, but this is some other voodoo. The manual contains a 'Theory of Operation' which states: "The Power-Line Rectifier consists of CR412, CR413, CR414, CR417, C418, L417, and L418. This section acts as a voltage doubler and rectifier when operating on 90 to 136 volts ac. In Option I, the section acts as a bridge rectifier when operating on 180 to 250 volts ac, and as a dc filter when operating on 180 to 250 volts dc. Its output is approximately 330 volts dc which operates the Battery Charger Converter."Can anyone enlighten me as to how the voltage doubler works, and how the optional capacitor switches it off?Many thanks,G

author: tautech
author_rank: Super Contributor
timestamp: October 09, 2014, 12:20:37 pm
content: C412-412 are mains filtering incorporating X & Y rated caps as is commonly done.The MURATA - DEBF33A103ZA2B - CAPACITOR, 0.01UF 1000V is the correct one for C416.

author: gareth
author_rank: Contributor
timestamp: October 09, 2014, 12:40:32 pm
content: I think you are saying that other capacitors, namely C412, C413 and C414 are mains filtering, and should be X & Y rated - but this optional capacitor C416 doesn't need to be class X & Y rated and therefore I can go with the other capacitor. Thanks for the advice!Let me know if I've misunderstood this, and I would still like to understand what this line to the midpoint of the output capacitance is doing in either configuration! I am trying to work through what happens in the case of a positive and then negative part of the cycle, but my brain is struggling!Kind regardsgareth

author: David Hess
author_rank: Super Contributor
timestamp: October 09, 2014, 01:53:06 pm
content: Quote from: gareth on October 09, 2014, 12:40:32 pmI would still use an X class capacitor for C416 but . . .QuoteOption 1 removes the jumper at position of C416 and replaces it with the capacitor.When the jumper is in place for 120 VAC operation, the bridge rectifier and input capacitors C417 and C418 operate as a voltage doubler producing about 340 volts DC. With the jumper removed, no voltage doubling takes place and the 240 VAC input produces about 240 volts DC. I think capacitor C416 is just there for RFI filtering.

author: Fraser
author_rank: Super Contributor
timestamp: October 09, 2014, 04:20:26 pm
content: I bought a 213 a while back with a view to restoring it. I haven't bothered to even fire it up since purchase. Is the 240V model so suitable for the UK. I would sell it if you are interested. Its in generally OK shape but the front of the plastic knobs have cracked off and all the side knobs are missing. If you are interested let me know what it is worth to you as a spare parts donor for your unit.Aurora

author: gareth
author_rank: Contributor
timestamp: October 09, 2014, 04:33:31 pm
content: That's a really interesting offer Aurora, thanks - I'll certainly be needing it if the custom chips inside have blown!Such a shame it doesn't have the 'int' knob from the side - that's the only one that's missing on mine.Many thanksGareth

author: Fraser
author_rank: Super Contributor
timestamp: October 09, 2014, 04:45:35 pm
content: @GarethAll is not lost, I also have a 211 that I keep as a potential spare parts donorIt has all its knobs on the side.I attach pictures of the 213 that I have. As stated it is not in great exterior condition and when I just plugged it in it did show signs of life and then the power LED just faded away so it needs new batteries (no surprise !) GBP60 +postage and its your and that is less than I paid for it. I believe it is likely worth more if I parted it out as the case halves sell for GBP20 each and the custom chips sell for whatever the seller asksIf you want it complete you have first refusal. I have done absolutely nothing with it so it comes with no guarantee of functionality beyond my guarantee that I have not robbed it for any parts. It has the Option 1 fitted as shown in the last picture. It would certainly be a good insurance policy for your working unit.Updated.... I'll take GBP50 +p&p for the 213 plus a knob from the 211Pictures attached.Aurora

author: gareth
author_rank: Contributor
timestamp: October 09, 2014, 05:11:26 pm
content: Oooh, that is a very tempting offer, I know from lurking on ebay with saved searches etc that these things come up but not that often and usually a long way away! And now I know what that empty space is next to the serial number - for the optional option indication.My other and wiser half has suggested that perhaps one old broken oscilloscope is enough to be getting on with - I suppose she's right.I hope that others see the appeal of these things - when you see them in the flesh they are absolutely gorgeous - and yours gets some tlc.Many thanksGareth

author: Fraser
author_rank: Super Contributor
timestamp: October 09, 2014, 05:36:46 pm
content: No worries at all.You know where it is if you ever need it.Aurora

author: harrimansat
author_rank: Regular Contributor
timestamp: March 11, 2015, 09:43:05 pm
content: My everyday tools!