Two amplifiers with blown rectifier diodes, one no longer available. - Page 1
Forum section: electronics / beginners

author: Mp3
author_rank: Frequent Contributor
timestamp: July 21, 2021, 08:40:48 am
content: My problemI have been tasked with repairing two Bose PS1 speaker systems for a relative, this item about 15-20 years old.When doing Google research, I found several mentions where people stated they had brought the amp back to life simply by swapping rectifier diode "UF4006", and sometimes a nearby "31DQ10" which may become leaky.I've found on both units, UF4006 is completely dead. 31DQ10 is leaky on one and not a problem on the other. (i removed diode and tested out of circuit).UF4006 is that common factor of all dead Bose PS1 i see online. And on both the units I have for repair, there is some glue touching the leads on both end of UF4006, this glue is clearly burnt along with the diode on both units. (picture attached...)My questionUF4006 is available, but to prevent future failure of this part,should i choose Schottky diode instead of Rectifier diode?specs of UF4006 is Vr 800V, If 1A, Vf 1.7v, surge current 30A, reverse current 10 uA, recovery time 75ns. Or does it seem like glue on diode leads is more likely cause of failure? The only suitable Schottky diode i could find, is in TO-220 package,CSD01060A, but it has If Vrrm 600V, If 1A, Vf 1.8V, surge current 32A, reverse current 100 uA. So i'm not sure if that much higher reverse current is OK.Another option might be STTH110, but surge current only 20 A, so i'm not sure about it, since I don't know how much current actually flows across this diode during usage of the speaker.31DQ10 is not available, and it has strange specs, hard to find an equivalent.If 3.3A, Vf 970 mV, Vrrm 100 V, surge current 210A, reverse current 1 mA. The closest Schottky rectifier I can find SR3010-TP has If 3 A, Vf 850 mV, Vrrm 100V, surge current 80A, reverse current 1 mA. Not sure how much current goes thru this diode. I can also find SBYV28-100 by Vishay which is not Schottky but has If 3.5A, Vr 100V, Vf 890 mV, surge current 90 A, reverse current 5 uA, recovery time 20 ns.Are either of these acceptable? I see a few 31DQ10 on eBay from sketchy sellers, but I prefer to buy this part from somewhere reputable, if either of these alternative are acceptable.Thanks for your time.

author: BrokenYugo
author_rank: Super Contributor
timestamp: July 21, 2021, 09:09:58 am
content: It is generally unwise to try to outsmart the engineers by doing stuff replacing a silicon diode with Schottky, or the other way around. As to substitutions you need to have some idea of what the parts are doing in circuit to have an idea of what parameters are important.

author: Mp3
author_rank: Frequent Contributor
timestamp: July 21, 2021, 09:14:38 am
content: Quote from: BrokenYugo on July 21, 2021, 09:09:58 amThat's what I thought, but I wasn't sure if this diode "UF4006" was chosen to fail, or if the glue was put there so itwouldfail.What about the 31DQ10, which is no longer made - I'm not quite sure what do since it has If 3.3 A but Mouser & Digikey only stock Schottky with If 3.0A or If 3.5A. I really don't want to buy possibly fake diode from overseas.

author: perdrix
author_rank: Frequent Contributor
timestamp: July 21, 2021, 09:15:29 am
content: Normal reason for blown rectifier diode is some sort of short further on in the circuit causing excess current to blow the diode. So just replacing the diode may just result in it failing again.D.

author: ambrosia heart
author_rank: Regular Contributor
timestamp: July 21, 2021, 09:23:37 am
content: 31DQ10 is not available, and it has strange specs, hard to find an equivalent. Really?One word: taobao. Don‘t tell me they are fake. I alsorepair AV-amps. All components come from taobao.They work perfectly.Some say they buy fake goods from taobao due to greedy attitude. Always comparing prices, don‘t buy cheapest.

author: Mp3
author_rank: Frequent Contributor
timestamp: July 21, 2021, 09:25:39 am
content: Quote from: perdrix on July 21, 2021, 09:15:29 amI don't fully understand the aux power supply circuit, but I know combination of 31DQ10 and 1N5822 are rectifying 27V AC into +15 DC and -15 DC.schematic is here, the circuit i must repair is on page 10. D601 is rectifier diode Uf4006https://lensprojects.files.wordpress.com/2016/08/bose-ps1-l1-rev1-schematics.pdfI think, maybe UF4006 is not able to handle the current of the amplifier - it is most common failure in all these models, appearance of glue on leads seems to be to hasten death of diode, and is half the physical size of all other diodes in the same PCB.Still, even if I choose to use UF4006, I need to choose something to replace 31DQ10, this i really must ask for help with.

author: Mp3
author_rank: Frequent Contributor
timestamp: July 21, 2021, 09:29:23 am
content: Quote from: ambrosia heart on July 21, 2021, 09:23:37 amYou never have a problem with faulty parts this way?Maybe I will buy some from Aliexpress, I was just hoping to buy something close enough from Mouser, but if you are trusting those parts in amps, it gives me some confidence,

author: Mp3
author_rank: Frequent Contributor
timestamp: July 21, 2021, 10:57:11 am
content: Quote from: perdrix on July 21, 2021, 09:15:29 amThinking about this some more - I found rectifier diode UF4006 is going across MOSFET K2645-01MR similarly to the recommended circuit shown in the datasheet of this MOSFETI guess I will use UF4006, it is still available & the other alternatives I was considering were available at that time, so maybe the true cause of failure is the glue seen in that picture which burns and surely helps to bring the diode over safe operating temperature. I can't imagine that on so many of these units, the MOSFET is never what went bad, just some of these diodes, though i have seen other people who have UF4006 in fine shape but one of the rectifiers for +15 or -15 VDC has gone bad.I bought some Taobao 31DQ10, i guess if i want to spend much more time worrying about if i can improve these parts then i can spend this time simulating that circuit

author: wraper
author_rank: Unknown
timestamp: July 21, 2021, 11:06:01 am
content: Quote from: Mp3 on July 21, 2021, 09:14:38 amIf reliability is a problem, generally you should use a similar part but beefier. It's strange that you are willing to use Schottky as a replacement for usual silicon diode but are not willing to use a diode with 0.2A higher current rating. As if the current rating is some precise spec. Current rating says nothing about its parameters, only that manufacturer says that part should withstand such current. FWIW if other specs are the same, you can replace 3A part with 10A part. Not to say that rated current can be given at different conditions or safety margins which often makes such ratings not equal.QuoteLMAO, going trough hoops to buy some dodgy part which can be replaced with tons of other jelly-bean parts from reliable sources.

author: wraper
author_rank: Unknown
timestamp: July 21, 2021, 11:23:24 am
content: Part which is better at almost every spec thus will work fine and will be under less stress.https://www.mouser.com/ProductDetail/Vishay-General-Semiconductor/SB5H100-E3-73?qs=u91jd7aysvPrwEDBsSVksQ%3D%3D

author: Terry Bites
author_rank: Super Contributor
timestamp: July 21, 2021, 02:06:58 pm
content: Going higher in current rating by 200mA to 3.5 isn't going to cause any drama. The dseigner would have (should have) used worse case specs for the diode.From the schematichttps://www.google.co.uk/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwi0oPfgrfTxAhWNY8AKHd3gDMwQFjAKegQIBBAD&url=https%3A%2F%2Fmedias.audiofanzine.com%2Ffiles%2Fbose-ps1-l1-rev1-schematics-478018.pdf&usg=AOvVaw1ahnz8DUDxNiIYFjqC_0Qqyou can see that they have put snubber networks across the 31DQ100's. Not unusual in hifi psu's. So you don't need to worry about meeting recovery time specs. The caps following on are 35V so 100V diode is a conservatively rated. An SR510 R0 wouldn't be a bad choice.The diode in the picture D601 is having to work hard. Its an 800V part and I'd be surprised if you can get Schottky in small diode package that will manage that voltage. Its hard to see why they have snotted it to the pcb,is the a groundplane underneath thats being used as a heatsink? It looks a bit random.

author: wraper
author_rank: Unknown
timestamp: July 21, 2021, 02:30:30 pm
content: Quote from: Terry Bites on July 21, 2021, 02:06:58 pmOn taobao = it can be anything inside.

author: bdunham7
author_rank: Super Contributor
timestamp: July 21, 2021, 02:47:51 pm
content: Just use the parametric search at Mouser and select two 50-cent parts that are a bit better than what you have. Replace them with the same general types.I had a quick look and there are hundreds of candidates. How about UF3007G for the first and SR515 from Taiwan Semi for the second?There's a time and a place for scouring the world for original replacement parts. This isn't it.

author: wraper
author_rank: Unknown
timestamp: July 21, 2021, 03:23:10 pm
content: Quote from: bdunham7 on July 21, 2021, 02:47:51 pmSR510 is suitable. SR515 is not that good replacement as has higher reverse voltage but also higher forward voltage drop.

author: bdunham7
author_rank: Super Contributor
timestamp: July 21, 2021, 03:53:08 pm
content: Quote from: wraper on July 21, 2021, 03:23:10 pmTrue, but that is at 5 amps. If you look at the two datasheets (31DQ10 vs SR51x) , they show the Vfcurve differently--one has different temps, the other doesn't--but I think they're close enough that either would work. Then there's the leakage current, which is actually worse for the SR510 than the 31DQ10 at 125C. I don't know the particulars of the circuit--if it is 15 volts, then there's probably no reason to use the SR515, if its 60V, then maybe there is. My main point is that there are oodles of new, inexpensive,genuinereplacements that will all work fine.

author: wizard69
author_rank: Super Contributor
timestamp: July 21, 2021, 04:50:42 pm
content: Quote from: Mp3 on July 21, 2021, 09:14:38 amWhile out smarting an Engineer might not be a good idea, Engineers can and do make mistakes. However don't try to out smart them if you don't understand the circuitry underneath.On the other hand it is extremely common in the electronics world to substitute parts, especially transistors and yes even diodes with near identical once spec wise. There are massive books, well maybe web sites these days that cross referenced thousands of parts that in most cases worked as substitutes. These substitutes would work in most cases unless the engineer was relying upon a fringe performance spec.So if you can find yourself a similar technology component, with right specs, then you likely have a potential candidate replacement. Since you know this to be a common failure mode, I'm assuming you have had conversations with other techs repairing these units, if so there is likely to be a part known to work well as a replacement. So maybe ask those with experience with these units.QuoteI'm not sure which would be worse; a fake diode or one that is well specced but fails anyways. A substitution is likely to work if you know why the old has failed so often. Who knows the failure might be implementation related. I know nothing about this amp but I'd be very surprised to find out that there is no workable solution on the market that works as a substitution and might even be more reliable.As for Taoboa, never heard of them until today. Given that there must be legitimate suppliers of electronics in China. The problem of course is finding them, especially for low volume repair type work. I don't see why you wouldn't try them considering the cost of these parts is hardly a problem. Even if the parts are garbage, you have at least learned not to buy those diodes from them. Generally though I find going to China, for small parts orders, to be a high wall to climb. In these cases it is just easier to go local.

author: wraper
author_rank: Unknown
timestamp: July 21, 2021, 04:55:38 pm
content: Quote from: wizard69 on July 21, 2021, 04:50:42 pmThe problem is that counterfeit parts often work but are not up to spec. And they may work good or long enough that you won't figure out it was a counterfeit. Or you will look for other problems in the circuit because your replacement blows up after a while, which often happens with legitimate parts if there are other issues.

author: Mp3
author_rank: Frequent Contributor
timestamp: July 22, 2021, 03:43:56 am
content: Quote from: bdunham7 on July 21, 2021, 02:47:51 pmThank you very much for this, i'm going to go look at those two. I may have been searching incorrectly, but I was worried that the If current of 3.3A on the 31DQ10 was somehow integral to the circuit.I have ordered 20 units of 31DQ10 from the best rated Aliexpress seller I could find - cost me just under $8 - but I'm going to order something similar from Mouser just to see if i can at least get the ampworkingfor a short period of time, if only to know it's operational again.I was also able to find some diodes that seem to be a perfect drop-in if I stretch the forward current of the diode from 3.3A to 3.5A, which seems insignificant considering it's rectifying 15VDC, and I have an isolation transformer so i can power this aux power supply PCB out of circuit and keep an eye on it with the scope to be sure nothing funny is happening.

author: bdunham7
author_rank: Super Contributor
timestamp: July 22, 2021, 04:00:27 am
content: You can put higher-rated diodes in as long as you don't sacrifice other parameters, and in the case of current, you rarely do. Both of the ones I suggested will be animprovementover the originals, which will hopefully help your repair last longer.