Known-good measurements/values for Presonus Eris 3.5 PSU - Page 1
Forum section: electronics / repair

author: Elly D.
author_rank: Newbie
timestamp: August 19, 2021, 08:02:55 pm
content: Hello.I'm looking for known-good measurements or photos of some passives of the primary side PSU of the Presonus Eris 3.5 studio monitors.Board version is v1.2 (2018-05-04).I've already looked for typical application circuits in datasheets and application notes and some come quiet close, but do not 100% match:-https://www.st.com/resource/en/application_note/an246-uc3842-provides-lowcost-current-mode-control-stmicroelectronics.pdf(pg. 19, closest, non-100% match, no optocoupler)-https://www.ti.com/lit/an/slua143/slua143.pdf(pg. 13) (good, no 100% match)Specifically I'm interested in:- R49- C without designator below R49- C10 or C19 (hard to read, below R51)- R54- R60- R1, R61 (1210 in parallel)Diagnosis:- No char marks elsewhere except around the PSU controller.- Switching transistor Q3 shorted between drain and source- Components in the switching transistor path blown- UC3842B shorted across multiple nodes- F1 did it's job- The NTC is OK- Switched transformer winding ~200mOhm (sounds legit)Blown or bad measured components are marked with a red "x" in the partial, reverse-engineered schematic:(No guarantee that the schematic is 100% correct. U3 in the schematic is supposed to be U8.)Damaged area details:U8 marking:PSU bottom overview:Teardown guidance:- Remove all back plate screws- Unplug the cables- Discharge and check primary side caps (i.e. using Low-Z) or handle very carefully- Pull the knobs off and remove all screws to the connectors and stand-offs- Use a spudger to carefully lift the glued foam from the backplate around the connectorsRaw measurements from my notes:- NTC (undesignated, next to CN1) = 3.2Ohm- F1 = open- Q3 = TSF 10N60M- open on pins 1 and 2 / 1 and 3 (gate vs. source/drain)- shorted in both directions on pins 2 and 3 (source and drain)- U3 = UC3842B- Ground vs. Isense vs. Vin shorted- R61 = 191k- R1 = 180k- R61 || R1- R54 = 570k [with U3 removed]- C19 (C10) = 1.9k, capacitance not measurable, 34k [with U3 removed]- R51 = 9.4k, [also with U3 removed]- R49 = 17.9M, open with [with U3 removed]- Cx (undesignated, below R49) = open- R28 = 20k- C9 = capacitance not measurable- C58 = capacitance not measurable- R32 = 2k- C59 = capacitance not measurable- R31 = 14.9k- R60 = 6.5k- R36 = 19.8k- C57 = 26µF- R102 = 560k [with U3 removed]Thank you in advance.

author: crozac
author_rank: Newbie
timestamp: September 14, 2022, 09:51:55 pm
content: r61 and r1 = r500

author: mladen82
author_rank: Contributor
timestamp: February 09, 2023, 01:47:27 pm
content: Any further help, please post

author: Ashtar Sheran
author_rank: Newbie
timestamp: January 31, 2024, 04:41:48 pm
content: Hello, can someone told me the parametrs of U8 and Q3 part? I dont know what to order.

author: tunk
author_rank: Super Contributor
timestamp: January 31, 2024, 04:46:04 pm
content: Maybe this:https://www.st.com/en/power-management/uc3842b.html

author: Elly D.
author_rank: Newbie
timestamp: March 29, 2024, 05:02:40 pm
content: Thank you for the replies.On a later board with version 1.3, I could see these changes:- "C19 (C10)" is actually or now C10- CX (undesignated) is C55 nowThe board from my first post was v1.2.- R54 = 470 Ohm [in-circuit] (label=471) (0603")- R49 = 50 Ohm [in-circuit] (label=510) (0805")- R1, R61 = 500mOhm [in-circuit] (label=R500) (1206")- R60 = 10 Ohm [in-circuit] (label=100) (0603")- C10 in 1.3, (C19 in 1.2) measured=140nF (probably 100nF) (0603")- CX / C55 measured=140nF (probably 100nF) (0603")

author: spyro512
author_rank: Newbie
timestamp: April 07, 2025, 02:34:55 pm
content: Hey, did you succeed?My fuse blew and and I went full retard bridging it (thought it blew because of a voltage spike in my network), now I cooked the same exact zone you're exposing there.My plan is to replace the components and see if I can get this piece of crap working againThanks and regards