Yamaha PSS-A50 Keyboard Voltage Regulator Faulty? - Page 1
Forum section: electronics / repair

author: Timmox
author_rank: Contributor
timestamp: June 27, 2025, 10:41:08 am
content: Hi All,Thanks for taking time to look at my question.I'm working on a Yamaha PSS-A50 that won't switch on.I have tried USB power and battery power but the unit will not switch on. I have tested the SMD power button and that is switching as it should.I have traced the input voltage path to what I suspect is a voltage regulator. The input voltage via USB is 5.2v and the output voltage on this component is 3.735v. I suspect that the voltage output may not be correct.So my questions are can anyone identify the component and do you thing it's working correctly or not? (see pictures)Any help would be gratefully received,Tim

author: MathWizard
author_rank: Super Contributor
timestamp: June 27, 2025, 05:32:40 pm
content: IDK what chip that is, I don't think I've seen a 6-pin regulator before, it could be a MOSFET, or some sort of "power good" IC, that just passes input power, if everything is working. What voltages are on each pin, those 2 big caps are probably input/output, and there's possibly a voltage divider on pin 2 (although I don't see a via, or resistance markings). Can you post some more pic's and see what attaches to it ? Where else do these voltages end up ?

author: akatrinii
author_rank: Contributor
timestamp: June 27, 2025, 09:27:33 pm
content: https://eu.mouser.com/new/texas-instruments/ti-tps25200-efuse/Seems like a resettable fuse. Check with the datasheet.Perhaps the 5.2V you're getting is the USB Power and the 3.7V comes from the battery? Could you disconnect the battery and check the 3.7V is still there? 3.7V looks a lot like Lithium battery voltage. Cheers.

author: Timmox
author_rank: Contributor
timestamp: June 30, 2025, 07:16:20 pm
content: Thanks for your reply. I'll do some more tests when I'm back in my workshop on Wednesday and post the results. Cheers, Tim

author: Timmox
author_rank: Contributor
timestamp: June 30, 2025, 07:18:39 pm
content: Thanks for your reply. It is not rechargeable so doesn't have a lithium battery. It can power either by USB or 4 AA batteries. I'll post some more pictures when I'm back in my workshop on Wednesday.

author: Timmox
author_rank: Contributor
timestamp: July 02, 2025, 02:01:18 pm
content: After further testing of the 6 pin chip I'm getting 5.2v on the top right pin and I'm now getting 3v on all the other pins.I've attached some more photos of the board in context.

author: akatrinii
author_rank: Contributor
timestamp: July 03, 2025, 03:52:01 pm
content: Having 3v on all other pins seems quite strange. There should at least be one Ground connection. Please refer to the attached photo with pinout.Also please measure the resistor I have circled in Blue, should be between 33kohm and 1100kohm.

author: Timmox
author_rank: Contributor
timestamp: July 04, 2025, 09:35:00 am
content: Hi akatrinii,Thanks for your help. I'll do that and report back.Cheers,Tim.

author: Timmox
author_rank: Contributor
timestamp: July 04, 2025, 02:50:12 pm
content: I've tested the resistor you've circles and it measures 150k. The one joined to it measures 43k. Pin 6 Measures on the 6 pin chip measures 5.2v and all other pins measure 3v. The resistance between pin 6 and pin 5 is 420k. The voltage between pins 6 and 5 is 2v. There is no continuity between ground and pin 5 so it looks like it could be a ground issue. I have been using the metal surround of the USB port as ground. The 6 pin chip is not getting hot.Cheers

author: Potential Resistor
author_rank: Contributor
timestamp: July 04, 2025, 05:32:34 pm
content: Just attempting to help. Do you think it could be one of these (the small SKB branded ic):ADG779BKS"The ADG779 operates from a single supply range of 1.8 V to5.5 V, making it ideal for use in battery-powered instruments"Datasheet:https://www.analog.com/media/en/technical-documentation/data-sheets/ADG779.pdf

author: fzabkar
author_rank: Super Contributor
timestamp: July 04, 2025, 06:22:13 pm
content: Quote from: Timmox on July 04, 2025, 02:50:12 pmYou could try bridging Vin and Vout with a fuse, or wire link if you are confident that there are no shorts downstream. That would test the rest of the circuit. Of course, this assumes that the component is indeed a load switch or e-fuse.

author: akatrinii
author_rank: Contributor
timestamp: July 04, 2025, 10:14:10 pm
content: Do you have a hot air station? If so, remove the chip and measure the voltage on Pin 6 (using ground pin 5, central Pad, Usb outer shell). If you don't get 5V there the problem is before this small chip.

author: Timmox
author_rank: Contributor
timestamp: July 05, 2025, 07:51:50 am
content: Yes I have a hot air station. I will remove the chip and report back.Thanks again for your help.

author: Timmox
author_rank: Contributor
timestamp: July 05, 2025, 11:19:14 am
content: Hi akatrinii,I took the chip off and was still getting no ground. Traced it back and the ground has a fuse that's gone (see image). I was expecting a fuse on V+. I should have checked both but you learn more every day.Thanks for your help with this one. I've learnt a lot.Cheers,Tim

author: wraper
author_rank: Unknown
timestamp: July 05, 2025, 11:38:23 am
content: This resistor looks like it could be cracked.

author: Timmox
author_rank: Contributor
timestamp: July 05, 2025, 12:14:35 pm
content: Hi Wrapper,It does but it isn't. I've check it and it's fine. It's 150k.I've found the issue, it was a fuse on the ground rail.Thanks for you help,Tim.

author: akatrinii
author_rank: Contributor
timestamp: July 06, 2025, 05:40:22 pm
content: Is the board fixed?