Technics SA-103 XL - Keeps Blowing a fuse - Page 1
Forum section: electronics / repair

author: Matty85
author_rank: Newbie
timestamp: October 13, 2025, 06:48:51 am
content: Evening All,I have a Technics SA-103 XL Receiver that keeps blowing a fuse. It used to work perfectly, but recently I got it out of storage and now it blows a fuse every time I turn it on at the power switch.Anyone have any ideas what may be triggering this?NOTE: I've attached a few snap shots of the schematicsXL is for Australia model (240V)Thanks for your timeMatt

author: frantisek
author_rank: Regular Contributor
timestamp: October 13, 2025, 09:20:37 am
content: It's clear that there's a short circuit somewhere behind the fuse. You have to measure something too!

author: David_AVD
author_rank: Super Contributor
timestamp: October 13, 2025, 09:29:47 am
content: Use the diode test on your meter to check D701, D702, D703 & D704 in circuit.If they test ok, check for a short across each of the main filter capacitors or a short between the main positive and negative voltage rails.

author: Kwakerman
author_rank: Regular Contributor
timestamp: October 13, 2025, 09:35:03 am
content: I'd disconnect and insulate the Blk, Brn and two Blu transformer wires from the pcb and see if it still blows the fuse, if it does the transformer is likely faulty.If it doesn't blow reconnect the Blu and Brn and try again, if still ok then reconnect one Blu at a time to see which side of the power supply is at fault.

author: Matty85
author_rank: Newbie
timestamp: October 13, 2025, 11:39:39 am
content: Hi Frantisek,Thanks for the reply.What would I have to measure?Sorry, I'm only a beginner here

author: Haenk
author_rank: Super Contributor
timestamp: October 13, 2025, 02:03:33 pm
content: No cap in there that could go short.You really need to check every single connection, unfortunately.Most likely, the primary winding of the transformer has shorted, so check for very low resistance there.

author: themadhippy
author_rank: Super Contributor
timestamp: October 13, 2025, 02:45:56 pm
content: Quotewas the storage dry? dampness may of got in somewhere and causing a short,before you start delving in with a meter do as suggested above and disconnect the secondary of the tranny

author: David_AVD
author_rank: Super Contributor
timestamp: October 13, 2025, 09:27:10 pm
content: Quote from: Haenk on October 13, 2025, 02:03:33 pmThe caps across the main rectifier diodes most definitely can go short. I've seen it first hand multiple times.The reason for me saying to measure the main filter caps is that they are an easy measurement point for the main supply rails.

author: Haenk
author_rank: Super Contributor
timestamp: October 13, 2025, 09:58:35 pm
content: Quote from: David_AVD on October 13, 2025, 09:27:10 pmSure, but that would unlikely blow the primary side fuse (though maybe cause a short on the secondary side, causing a short on the primary side, but that would be a very unfortunate case). Still needs a bit of poking around for shorts anyway, maybe it's even a broken switch, shorting out contacts?

author: David_AVD
author_rank: Super Contributor
timestamp: October 13, 2025, 10:25:17 pm
content: A shorted cap across a main bridge diode most definitely can blow the mains fuse. I've seen it more than once, hence me mentioning it.

author: Matty85
author_rank: Newbie
timestamp: October 13, 2025, 11:34:53 pm
content: Thanks for all the replies - Much appreciated.I did find some surface rust under the transformer, suggesting moisture has gotten in somewhere.So, I'll starting the transformer and let you know.Thanks again everyone.

author: Andy Watson
author_rank: Super Contributor
timestamp: October 13, 2025, 11:43:50 pm
content: Is the fuse being replaced with the correct type? The "T" designation indicates it an anti-surge fuse. Ordinary fuses, i.e. not T delay fuses, will blow. Also, the physical construction of a T fuse is such that they can effectively wear-out over time.