Help/Advice needed diagnosing circuit - Page 1
Forum section: electronics / repair

author: jbo
author_rank: Newbie
timestamp: March 17, 2017, 06:11:29 pm
content: Hello EEVForum, I am a pc tech who has recently developed an electronics hobby and have been watching Dave's videos for quite a few months. I am new to electronics other than some hobby level stuff and new to forums in general so forgive me if i violate at protocol or etiquette. I have a circuit from an inspection machine for automobiles i have been trying to troubleshoot. It has no visible signs of damage other than a little corrosion in 2 or 3 spots but appears to function fine other than a usb port that is used for a data backup is receiving no power. One question i have is if the usb controller ic (CY7C63001A-PC) would prevent the vcc lines on the port from receiving power or if it is just used for data. The board number for the whole circuit is EAP0215E20A, I not bee successful in finding a diagram. Any help or advice is greatly appreciated.(i will add a photo later if i am able)

author: tpowell1830
author_rank: Frequent Contributor
timestamp: March 17, 2017, 06:16:07 pm
content: Hi jbo, welcome to the forum.Yes, a photo (or several) would help and a schematic drawing as well. Or, even a sketched drawing of the circuit that you reverse engineered. The corrosion doesn't sound good.

author: Nusa
author_rank: Super Contributor
timestamp: March 17, 2017, 06:43:04 pm
content: That usb controller does not control the power line. In general, USB power and ground are always connected. If they weren't, memory sticks wouldn't have input power, and would not function. Sounds like you need to trace the 5V power on that board and see where it stops, if it's even present at all.Corrosion on PC boards is always bad. Pictures would help a lot on that. Given your power symptom, it could easily be something like leaking capacitors that need to be removed, board repaired, and replaced.

author: jbo
author_rank: Newbie
timestamp: March 17, 2017, 08:04:06 pm
content: Thank you for your replies, i have added a picture and have more but the file size limit is killer. i am unable to find a schematic online and i may be able to make a sketch although it will take a while due to lack of experience. the led (d1) does blink when powered on however to led by the usb ic does not. the usb port closest to the sun logo p10 connector is the one that does not receive power

author: Paul Moir
author_rank: Frequent Contributor
timestamp: March 17, 2017, 08:13:23 pm
content: Up next to the USB connector, the one next to the power connector, is a fuse labeled "F5" which looks like a disc capacitor. Is it connected to the USB and if so, is it still good?

author: jbo
author_rank: Newbie
timestamp: March 17, 2017, 08:15:19 pm
content: I believe so, i have tested it with a multimeter along with the other fuses i could identify.  just double checked it, it is good. Unfortunately i am about to leave my shop and will not be back untill monday.

author: cncjerry
author_rank: Unknown
timestamp: March 17, 2017, 10:01:06 pm
content: Try another USB cable?

author: jbo
author_rank: Newbie
timestamp: March 20, 2017, 04:01:46 pm
content: ive already tested the power lines to the port.. As soon as i get the time i am going to remove the caps from circuit and test them. Will update

author: jbo
author_rank: Newbie
timestamp: March 22, 2017, 04:45:47 pm
content: Ok, finally got back to the board and decided to follow Nusa's suggestion and traced the 5v pin on the port to the part labeled in the attached picture, however i am have trouble finding a datasheet for the part. The markings are 35v 0132 JC so i think it may be a capacitor? it is attached to the 5v line on the psu.