RIFA  cap replacements for Tektronix 2465B - Page 1
Forum section: electronics / testgear

author: Bosteve
author_rank: Newbie
timestamp: January 14, 2025, 01:47:08 pm
content: First off, I should note I am a hobbyist that works on tube stereo equipment. That said, I have a Tek scope that I use occasionally. My scope blew a couple safety caps a while back. Ive been hesitant about disassembling it. However, I've gone through several posts regarding teardown and repair and now have it on the bench.In my case, the RIFA safety caps, C1016 and 1018 failed, as well as R1016. I am now sourcing replacements.The inverter board also has RIFA caps at C1052, C1051 and C1020. Everything Ive seen says to replace the them. As I understand safety caps, C1020 and C1051 go to ground, making them Y rated. As for C1052, I know I can use a Y cap, but would like to know what the schematic calls for, just for my own knowledge. One of the 2200pF caps is in a very tight location, so I plan to use a new Kemet/Rifa, since it is a direct replacement. Even though it is metalized paper, I assume new caps will last long enough for my use.Also, in one thread the OP said he used ceramic resistors at R1016 and 1018. Is there a reason for this? And since there is no wattage designation on the schematic, can I assume 1/2 watt will be fine or should I bump them to 1 watt?Thanks

author: srb1954
author_rank: Super Contributor
timestamp: January 14, 2025, 02:03:48 pm
content: Quote from: Bosteve on January 14, 2025, 01:47:08 pmIn the event of a fast surge coming in from the mains supply the line safety capacitors pass most of that surge voltage directly through to the resistors creating a very high pulse power dissipation in the resistor. Ceramic composition resistors are good for handling such power surges without damage but carbon composition resistors are also quite good for handling surges and it is this type would likely have been originally used by Tek. Do not use a metal film or carbon film resistor as a substitute as these are much less capable at handling high peak power surges.Check the description in the BOM for these resistors as this should tell the type and power rating.

author: tggzzz
author_rank: Super Contributor
timestamp: January 14, 2025, 03:15:05 pm
content: You can find the full service manuals (and much more) at the TekWikihttps://w140.com/tekwiki/wiki/2465BNote also the NVRAM and SMD caps on the A5 board.Seehttp://www.condoraudio.com/wp-content/uploads/Projects/Tektronix-2465B-Oscilloscope-Restoration-Repair.pdfWhile you are in there you might want to recap the PSU.See the exhaustive 2465B thread on this forumhttps://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/

author: Kean
author_rank: Unknown
timestamp: January 14, 2025, 03:57:59 pm
content: Just for reference, the brand of the original capacitors is RIFA not FIFA.Some lovely photos shared by someone here...https://www.eevblog.com/forum/chat/old-rifa-capacitors-and-a-disaster-story/

author: Bosteve
author_rank: Newbie
timestamp: January 14, 2025, 04:17:17 pm
content: I knew that. Ill correct the error.Thanks.

author: Bosteve
author_rank: Newbie
timestamp: January 14, 2025, 04:28:03 pm
content: Im having trouble finding the BOM for the scope referred to by srb1954.The boards I'm working on are on pages 439-443 of the manual, but I don't see any specs for type and wattage of the resistors. Only the value on the schematic.

author: tggzzz
author_rank: Super Contributor
timestamp: January 14, 2025, 05:03:09 pm
content: Use the forum search facility to look for R1016. You will findhttps://www.eevblog.com/forum/testgear/tektronix-2465b-oscilloscope-teardown/msg5698791/#msg5698791Follow that link and again search for r1016 in "this topic", and you will find quite a few results.Also search the groups.io TekScopes forum messages; this is frequently discussed there.From memory there is quite a lot of space around those resistors, so just choose the physically largest that you can fit.Capacitor kit:https://www.etsy.com/listing/1612217040/tektronix-oscilloscope-repair-kit-2445acontains some resistors.States...BEFORE you place your order, you MUST send me CLEAR photos of your Tekscope's PCB's.Because of hundreds of UNDOCUMENTED production changes, I need CLEAR photos of these EXACT PCB's - A1 A2 A3 A4 A5 A9 A14.One photo per PCB; photograph the entire PCB.Simply informing me of your machine's serial number is NOT sufficient!ONLY by referencing these photos, am I able to make up the EXACT custom parts kit for YOUR machine.I CANNOT ship your kit, UNTIL you have sent me these photos.

author: Kean
author_rank: Unknown
timestamp: January 14, 2025, 05:06:50 pm
content: R1016 (A2A1R1016) is mentioned in the A2A1 assembly BOM on page 8-20 (PDF page 252) of the service manual fromhttps://w140.com/tekwiki/images/f/fd/070-6862-00.pdfSpec of R1016 is "RES,FXD,FILM:68 OHM,5%,0.5W".SPec of R1018 is "RES,FXD,FILM:30 OHM,5%,0.5W".

author: BillyGo
author_rank: Contributor
timestamp: January 14, 2025, 05:38:59 pm
content: Any random modern MKP cap will work here, can't really see the point of using RIFA paper cap unless for aesthetic purposes.Also, the only difficulty of replacing new safety caps will be desoldering those leads on GND. Tek likes to put wide ground traces on their pcb of psu.

author: wraper
author_rank: Unknown
timestamp: January 14, 2025, 05:53:58 pm
content: IMHO use Y ceramic safety capacitors instead. Barely anyone uses Y film capacitors these days.

author: David Hess
author_rank: Super Contributor
timestamp: January 14, 2025, 06:23:30 pm
content: The resistors are 5% and 1/2 watt. You can find this in the parts list in the service manual on page 8-28. The Tektronix parts book says they could be carbon film or carbon composition without distinguishing, but I am assuming they are carbon composition.I do not see good choices for replacements. Carbon composition and ceramic composition would be ideal, but are of limited availability. Maybe someone else can comment about using metal oxide or specialized film resistors that have high overload capability.I would take a close look at the lead spacing to see if a larger power resistor would fit. This will help with the overload and voltage rating. Replace the 30 ohm resistor with 33 ohms to make it easier to find.

author: Bosteve
author_rank: Newbie
timestamp: January 14, 2025, 06:48:26 pm
content: Knowing how to find the BOM is a huge help. Thanks.As for ceramic vs film caps, I will look into it. I will be using one 2200pf RIFA just because I can be sure it will fit in to its small space. For the others, I am not concerned.I do have one other problem. Taped to a handle was a component. After spending a couple hours pouring over every picture I could find, FireDragon's thread showed what is the 10MHz crystal. Apparently I had broke it off when removing or replacing the case when I first opened the scope up a few years ago. Looks like an easy fix.Regarding resistors, would 1 watt be wrong to use? I think recall reading they are sacrificial.

author: wraper
author_rank: Unknown
timestamp: January 14, 2025, 07:14:55 pm
content: Quote from: Bosteve on January 14, 2025, 06:48:26 pmI'd avoid using Rifa/Kemet paper capacitors at all costs. Knowingly using a ticking time bomb is not a smart thing to do. Moreover, if you use one that is Rifa branded, it means it's an old stock that already used up half or more time till blowing up.

author: factory
author_rank: Super Contributor
timestamp: January 14, 2025, 08:12:33 pm
content: The resistors that failed in mine, were replaced with fusible/flameproof resistors of the same power rating as the original parts. I can't understand why some increase the wattage, unless they prefer extra crispy PCB in a fault condition.David

author: David Hess
author_rank: Super Contributor
timestamp: January 14, 2025, 08:18:44 pm
content: Quote from: Bosteve on January 14, 2025, 06:48:26 pmI do not think it matters what type of safety capacitor is used, beyond being an X or Y type of the proper capacitance and voltage rating. I would be more concerned with lead spacing and whether it fits properly. Maybe someone else here can comment about differences between ceramic, plastic, and paper safety capacitors.QuoteThe resistors are sacrificial in the sense that they need to fail in a safe manner, or handle overload gracefully which being larger helps with. Usually film resistors fail poorly, but they make "fusible" film resistors which might be acceptable. Carbon composition resistors were great in this sort of application.

author: David Hess
author_rank: Super Contributor
timestamp: January 14, 2025, 08:20:53 pm
content: Quote from: factory on January 14, 2025, 08:12:33 pmLarger resistors have greater overload capability and a higher voltage rating.

author: chilternview
author_rank: Frequent Contributor
timestamp: January 14, 2025, 08:35:11 pm
content: I replaced the RIFA 2200pF capacitors with KEMET / PHE850EA4220MA01R17And the 0.01uF with KEMET / PHE850EB5100MB04R17They have the same pin spacing and similar size as the original RIFA's.

author: tooki
author_rank: Super Contributor
timestamp: January 14, 2025, 08:45:46 pm
content: Quote from: wraper on January 14, 2025, 07:14:55 pmYou sure about that? Even now that Kemet is in the process of being rebranded to Yageo, the freshly-updated (July 2024) datasheets for some products continue to show RIFA branding on the product photos. (An example is attached.)

author: wraper
author_rank: Unknown
timestamp: January 14, 2025, 09:36:24 pm
content: Quote from: tooki on January 14, 2025, 08:45:46 pmI was quite sure they changed the branding but on checking it looks like they put Kemet branding only on paper RC units.https://content.kemet.com/datasheets/KEM_F3089_P409_X2_275.pdfEDIT, nope, they put KEMET branding on regular paper capacitors too. For example they sell PME278 as RIFA but the same thing under KEMET branding as P278https://content.kemet.com/datasheets/KEM_F3087_P278_X1_480.pdfQuotehttps://connect.kemet.com:7667/gateway/IntelliData-ComponentDocumentation/1.0/download/specsheet/P278HE102M440A