Tektronix 2465A Carbon Composite Resistors - Page 1
Forum section: electronics / repair

author: Stonie
author_rank: Newbie
timestamp: December 28, 2023, 02:22:54 am
content: Hi All,Newbie here with a “new to me” Tektronix 2465A on the way from Japan and not sure if this post is in the correct section, so here go's...I’m in the middle of conducting research in readiness for servicing this scope upon arrival; electrolytics replacement, U800 heatsink… plus a few other mods.However, it's getting on for 30+ years old now and I know full well ‘carbon composite’ resistors are notorious for drifting out of spec with age; and so far, I’ve been unable to find any info. on recommendations for replacing them in these scopes.My question is a simple one… Is it recommended to replace these carbon composite resistors and if so, with which type ?TIA, Phil.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: December 28, 2023, 05:52:35 am
content: If the scope works fine and dandy, and its calibration issues can be fixed with the calibration procedure, then you won't need to replace the resistors.But I think carbon film or metal film will suffice if you do end up needing a replacement.

author: coppercone2
author_rank: Super Contributor
timestamp: December 28, 2023, 06:34:02 am
content: i use metal oxide as carbon composition replacements. only thing i would be worried about is like high frequency voltage dividers or something if they have em.if you run into a problem caused by one, there is ceramic composition resistors. Cost a pretty penny and only 10% accuracy. I imagine if you had to buy a bunch of those to get a specific value its a bad day financially.

author: factory
author_rank: Super Contributor
timestamp: December 28, 2023, 10:28:42 am
content: There aren't many in the pictures I can see, those that are used will be for higher pulsed voltage rating, would need something bigger in size for those.In certain high frequency areas they used them as they are non-inductive.Also don't increase the size of fusible resistors in the PSU.Apart from replacing the RIFAs (with fusible resistors if blown), Schaffner line filter and the peeing electrolytics, I haven't done anything else to mine, unless there was a fault.If it ain't broken, fix it till it is.....David

author: tggzzz
author_rank: Super Contributor
timestamp: December 28, 2023, 06:51:40 pm
content: Quote from: Stonie on December 28, 2023, 02:22:54 amEvery repair carries the risk of damage, so you have to balance the risk/reward.Which composition resistors are you thinking of? I haven't seen any problems (2*2465, 1*2445B).Definitely replace the RIFAs (see the Condor Audio guide).While you are "in there" probably replace the main PSU electrolytics. I can't remember which 2465* variant has the description of two caps swapped - so remove and replace one capacitor at a time.If the U800 is working, don't touch it. Due to appalling mechanical design, there is a significant chance you will damage something.Any potentially leaky electrolytic caps on the A5 board near the ADC/DAC should be replaced.If that scope has the "squirrel cage" motor/fan, be very careful to follow instructions as to how you remove the collett. It is very easy to damage, even if you follow the correct method.Finally, have fun: they are nice scopes.

author: Stonie
author_rank: Newbie
timestamp: December 29, 2023, 07:20:18 am
content: Thanks for the input guys... RIFA's are also in hand.Just one other thing, any issues using low ESR caps ?