Onkyo TX-SV525R Blown Transistor - Page 1
Forum section: electronics / repair

author: maverick4400
author_rank: Newbie
timestamp: December 11, 2018, 09:56:36 pm
content: Hello,I've got an Onkyo TX-SV525R which displays "Protect" on display and a quick observation reveals that one pair of its transistors are blown. The transistors are B1557 and D2386. After a research for a replacement I thought that i found even better transistors which are 2SA1943 and 2SC5200. Many values are more or less same except the ones which I found has double the power rating. I measured the dual package 0.22Ohm resistor and compare with other channels and it seems ok.When I replaced the transistors, the amplifier worked for 3-5 minutes and blown the replaced transistors. Now I want to ask the experienced professionals that what i did was ok or not? Both cases any suggestions are very welcomeThank you.Note: This value is very different than the original one.OriginalTOSHIBA Transistor Silicon PNP Epitaxial Type (Darlington Power Transistor)2SB1557 DC Current Gain: 5000-30000ReplacedTOSHIBA Transistor Silicon PNP Triple Diffused Type2SA1943 DC Current Gain: 55-160

author: Chris56000
author_rank: Frequent Contributor
timestamp: December 12, 2018, 03:23:57 am
content: Hi!You can't substitute a bipolar darlington 2SB1557 with a 2SA–etc., ordinary type, as the drivers can't handle the base current needed to drive standard transistors!You can get the original devices from fleabay, altho' there is the thorny question of "fakes", which you can't fully test without a high–voltage curve tracer to ensure they meet the original 140V Vcbo/Vceo specifications!My recommendation would be to look on fleabay for the originals, but don't get the cheapest ones you find, try to go for ones about 25–40% more than the cheapest from a seller who offers a replacement or money back guarantee!Unfortunately the failure of the replacements you tried could have damaged the driver–transistors further back, so you might have to do some detective work!S.M. from Electrotanya, altho' why whoever scanned it didn't include the pcb component–layout diagrams I'm not sure! All the circuit diagrams (schematics) are included tho!Get a pair of Matched Complementary pnp/npn TO3P Audio Power tr ansistors, 140V 15A or better, hFE 5000 min, either originals or equivalents, from eBay, Mouser or Digi–Key, (Digi–Key list 2SB1560s which should be OK) download the Service Manual if you've not already got it, then come back if you're still stuck and either myself or other Members will be glad to assist!Chris WilliamsPS!Please don't forget the 0.22R low value emitter resistors in series wirh the emitters – these may need replacing as well!

author: maverick4400
author_rank: Newbie
timestamp: December 12, 2018, 12:11:16 pm
content: Thank you Chris,These are very valuable information. I will start by searching the suitable replacement and study on the service manual. I will write my progress.

author: slbender
author_rank: Regular Contributor
timestamp: January 01, 2019, 07:16:01 pm
content: I agree, you cannot replace with a BJT in a circuit specifically designed where a Darlington transistor is required. I don't mean to steal this thread but the prior response has brought up another issue that I have had recently. I was always taught that 2SAxxxx/2SCxxxx were BJT transistors and 2SBxxxx/2SDxxxx were Darlingtons.However, I purchased in the past month (12/2018) pairs of 2SB1560's / 2SD2390's reportedly genuine Sanken parts, from four different Sellers on eBay. The first Sellers parts (low priced) all measure with "gains" between 100 to 180; the parts from Seller #2 (higher priced) measured gains of high 90's to 250, with an internal diode from Collector to Emitter. I used three different Chinese transistor testors, which all agreed that these were BJT's not Darlingtons.I have seen other part numbers of Darlingtons that measure as Darlingtons, with gains upwards of 12,000 to 20,000+ when tested on the same testers, but again, other identical looking parts, which measure gains of under 100. From that I conclude, all these genuine Sanken parts are fakes - BJT parts relabeled as parts that should be Darlingtons, but do not measure as Darlingtons. I also suspect it is very likely the parts I bought from the last two eBay Sellers, which will arrive in two or three weeks, will also be relabeled "fakes" and will measure as BJT's. Other parts that seemingly come from other manufacturers, may similarly be fakes also, this includes parts with a big "K" and parts with a fancy "T".The conclusion is - buy from First Line Distributors, like Digikey or Arrow, (not an endorsement of any one over any other) when it is important to get the proper part, even if it is triple the cost, there are lots of fakes being touted as "genuine". Second, Test, Test, TEST the parts, and match them where possible, a few of those twenty dollar transistor tester boards with multi-line readouts, do an excellent job of telling you what you have, from Resistors, to Caps, to Diodes, to Transistors, and more! The only thing those testers won't tell you, is the Wattage of Resistors. One place (famous name First Line Distributor) that won't be named, sent me Two Watt Resistors that look like 1/8 Watt from their size, and I am still not believing they are two watts! Even the best of the best screw up sometimes, or get fooled, Buyers Beware!-Steven

author: maverick4400
author_rank: Newbie
timestamp: January 10, 2019, 10:33:04 am
content: Thank you Steven,From now on I am going to test the components. I have 100uF capacitors which are labelled wrong because whole 10 of them shows 50-60 uFI am still waiting the transistors and when they arrive i will test with my transistor tester.

author: commongrounder
author_rank: Frequent Contributor
timestamp: January 11, 2019, 05:35:11 pm
content: Quote from: slbender on January 01, 2019, 07:16:01 pmThe difference between the 2SD/B family and the 2SC/A family of transistors is frequency range. D/B are low frequency and C/A are high frequency (generally). There are darlington parts in both families, so you have to look up the specific number to know for sure.The counterfeit semiconductor problem really aggravates this because the counterfeiters often don’t understand the difference and mislabel parts, to our extreme frustration. As others have said, don’t trust any seller but the big distributors to have legitimate parts.