Newbie needs Help with Philips3065 PSU - Page 1
Forum section: electronics / beginners

author: Lazarus
author_rank: Newbie
timestamp: August 29, 2022, 07:12:50 pm
content: Hello from a Newbie,i have struggle with my new repair candidat a Philips3065 Oscilloscope. From the outside it looks perfectly fine but on startup it releases a terrible squealing sound without any other signs of life. I have tried every suggested repair method i could find in this forum so far like changing the RIFA caps and all electrolytics but sadly nothing changed. What i can tell is that the Thyristor BT151 and the transformer behind it are getting really hot. I hope anybody has an idea what i can try to get this thing back in service again.

author: inse
author_rank: Super Contributor
timestamp: August 30, 2022, 05:48:45 am
content: Squealing sound might point to short circuit on the secondary side.There is no difference whether its connected to the load or open?Did you check the secondary side diodes and capacitors?What is the power consumption?Do you have a schematic for the power supply?Greetings from Bavaria

author: strawberry
author_rank: Super Contributor
timestamp: August 30, 2022, 06:32:36 am
content: someone who watch avengers will just ruin this engineering marvel

author: Lazarus
author_rank: Newbie
timestamp: August 30, 2022, 05:42:16 pm
content: Hello inse,my first suspect was the primary side because of the complete absence of any life sign besides the horrible sound.Capacitors are checked and okay. Diodes are a little tricky, i have found a few that looked like dead short at first but after desoldering one leg appeared absolutely fineThe sound is present with or without the crt-tube attached.Schematics are attached.@strawberry i have no intentions to get to a Tony Stark-Level, at the moment iam happy if i solder in my electrolytic-caps the correct way

author: inse
author_rank: Super Contributor
timestamp: August 30, 2022, 06:44:31 pm
content: Check all the voltage rails for short circuit.Interrupt the supply for the HV circuit, thats the most critical rail.The power supply is one of those discrete circuits that only the designer can explain instantly.

author: Ice-Tea
author_rank: Super Contributor
timestamp: August 30, 2022, 06:52:21 pm
content: Pretty sure this was one I sold and refurbed? How long ago did you get it? If its not years ago, drop me a PM and maybe I can help in some way...

author: Lazarus
author_rank: Newbie
timestamp: August 30, 2022, 08:09:25 pm
content: Quote from: inse on August 30, 2022, 06:44:31 pmThanks, i will do that and report my results.For a beginner i have real struggle with this one. The circuit explanations in the manual are very helpful but my “lab-equipment“ is not up to the task (this thing was bought as an upgrade for my 20Mhz HAMEG 205-3)

author: strawberry
author_rank: Super Contributor
timestamp: August 30, 2022, 08:37:51 pm
content: R6002,R6003 is startup resistorsV6014,V6017 darlington power switchC6009 timing capacitorV6009,V6012 15V limiterV6013 scrR6002,R6003 turn on V6014,V6017when R6017,R6018 reach 1,35V then V6013 turns on and then turns off V6014,V6017timing capacitor receive flyback voltage from transformer pin2 and resets V6013repeat

author: Ice-Tea
author_rank: Super Contributor
timestamp: August 31, 2022, 03:37:40 pm
content: To those wondering what I was smoking assuming I sold and recapped this scope somewhere in the past: these are pictures from a board I did recently. I sold one or two in the past with the same recapping

author: Lazarus
author_rank: Newbie
timestamp: August 31, 2022, 07:45:52 pm
content: @Ice-Tea i love the wuerth caps they are good quality and it is later easy to spot which caps are new because of the bright red color@strawberry thanks for the explanation i do my best to follow everything and give a reply when i have my results (hopefully with a working unit)