replacing rectifier diodes - Page 1
Forum section: electronics / repair

author: adcurtin
author_rank: Contributor
timestamp: July 07, 2018, 12:03:05 am
content: I just bought some old audio equipment. Unfortunately (well, maybe not) the main amplifier is dead. It's a Sony TA-V7.The short story is: the fuse was blown, when I measure across the mains I get 0.3ohms resistance. I think I've narrowed it down to 2 of the 4 rectifier diodes. They've failed short. They're be IR 30DL which seem to be 3amp 200v (which makes sense on 120v mains).Can I just replace them with any old rectifier diodes rated for mains?I can probably scrounge up either a full wave rectifier package or maybe even 4 other diodes in scraps I have, and it'd be awesome to get this going quickly.Also, any idea what could've caused these to fail? They were on the same DC side of the bridge, either both to positive or both to negative.

author: wraper
author_rank: Unknown
timestamp: July 07, 2018, 12:50:25 am
content: You can replace them with any other diodes which have same or better voltage and current ratings.

author: german77
author_rank: Regular Contributor
timestamp: July 07, 2018, 12:57:09 am
content: I don't see why not. It's not like special diodes are used in audio equipment. Diodes are hard to destroy if they are in well designed unless something else fails. Most like it some kind of transistor or mosfet. You should find it next to a heat-sink. It should be easy to spot once you remove the bad diodes and start looking for shorts between ground and voltage rails.

author: wraper
author_rank: Unknown
timestamp: July 07, 2018, 01:12:52 am
content: If 2 diodes have failed, there is a very high probability it's just a rectifier fail IME. They experience high inrush current during switching on and if one diode fails often another one fails too due to current surge.

author: Chris56000
author_rank: Frequent Contributor
timestamp: July 07, 2018, 02:13:05 am
content: Hi!Do be aware tho', the primary-side MOSFET and some of it's associated driver components may also have failed - sometimes you are lucky with a simple rectifier failure and no other fault, but I would meter across the mains reservoir capacitor (typically 100 to 220uF at 400V can-type snap-in component) for further shorts after you've removed the defective diodes!If you have another failure, post as many pictures as you can, we can assist with it's repair! Have you had a look for the Amplifier's Service Manual?Chris Williams

author: adcurtin
author_rank: Contributor
timestamp: July 07, 2018, 04:13:01 am
content: Thanks everyone!I patched in a D5SBA60 bridge rectifier, and patched in a 5A fast blow (instead of the 6.3A slow blow, those are on the way). There's no longer a short across the mains, the resistance was 340 ohms, and changing. I plug it in and turn it on, and nothing. It still doesn't work. But the fuse doesn't blow, so the diodes definitely were a problem. The main filter cap is a little bulged and maybe should be replaced, but I have other problems to solve first.There's a relay inline that I don't think is energized, so now I'm digging into the service manual to try to track down why.https://www.dropbox.com/s/4qjh21sgf9z69d7/hfe_sony_ta-v7_service.pdf?dl=0edit:I found that R820, the 33ohm 5W slow start? resistor is measuring 120kohms. Maybe some sort of voltage spike on the input fried that. now to bodge in a a couple other power resistors I have to see if that fixes it.edit2: heck yeah! that fixed it. ordered the right 33ohm resistor, and should be good to go. Now I gotta see if I can figure out why the tuner input is really quiet. The rest work, including the phono, which was the most important

author: Lionered
author_rank: Contributor
timestamp: July 08, 2018, 03:49:52 pm
content: Be careful in replacing the diode with the use of soldering tools. Make sure also that it is within the required specifications to prevent untoward results.

author: Lionered
author_rank: Contributor
timestamp: July 09, 2018, 05:47:29 pm
content: I agree that it should be ok. Good luck to this task. However, if you can buy a new one, it's worth considering more.