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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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2SD2385 + 2SB1556 Transistors
I've just been done on ebay. Both output transistors on a Kenwood A-97 amplifier had blown. Ordered the pair from ebay, installed them, working, great. Turned it off to put it back together and noticed the heatsink was really hot on the repaired side. I found that the base voltage on both transistors was low. Swapped both transistors from the good side to the repaired side and its now fine. Put the new ones in the good side the and now the good side has got hot and all the voltages have dropped the same as they did when they were on the repaired side.
Does anyone know where i can get a genuine pair of these transistors at a reasonable price? |
#2
Posted to sci.electronics.repair
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2SD2385 + 2SB1556 Transistors
I've just been done on ebay. Both output transistors on a Kenwood A-97
amplifier had blown. Ordered the pair from ebay, installed them, working, great. Turned it off to put it back together and noticed the heatsink was really hot on the repaired side. I found that the base voltage on both transistors was low. Swapped both transistors from the good side to the repaired side and its now fine. Put the new ones in the good side the and now the good side has got hot and all the voltages have dropped the same as they did when they were on the repaired side. Does anyone know where i can get a genuine pair of these transistors at a reasonable price? What was the base-to-emitter voltage on the questionable transistors, when the amp is idling? How does it compare to the working parts? These parts (when genuine) seem to be Darlingstons, not just single transistors. You may have been sold a pair of mislabeled standard transistors instead - this would probably result in over-biasing and a high idle current. Or, possibly they're genuine parts, but have a higher beta than the ones for which the amp was spec'ed? The beta bin would be a one-character A, B, or C, possibly stamped on the lower left corner of the plastic. If that's the case, they might work OK with some adjustment to the idle/bias settings. TIP142/TIP147 *might* be acceptable substitutes although their gain seems lower. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
#3
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2SD2385 + 2SB1556 Transistors
"Dave Platt" These parts (when genuine) seem to be Darlingstons, not just single transistors. You may have been sold a pair of mislabeled standard transistors instead - this would probably result in over-biasing and a high idle current. ** For sure. Or, possibly they're genuine parts, but have a higher beta than the ones for which the amp was spec'ed? ** Nonsense. Output transistors are typically biased with a voltage that varies with the temperature of the heatsink. TIP142/TIP147 *might* be acceptable substitutes although their gain seems lower. ** The fact they have a Vce of 100V as compared to the originals with 140V is far more of a worry. The BDV65C and BDV64C darlington pair is closer at 120V Vce. The OP can measure the +/- DC rails see if the total is more than 120V. ..... Phil |
#4
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I tried using one of the new ones with an old complimentary one from the good side and this caused a massive imbalance in the idle bias 1.4v for the good one and 0.6 for the suspect one. Can i assume from these voltages that the replacement's are not darlingtons? 0.6v is right for a single transistor and 1.2v (approximately double) for a darlington? Regards |
#5
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2SD2385 + 2SB1556 Transistors
fruittool wrote in message
... I've just been done on ebay. Both output transistors on a Kenwood A-97 amplifier had blown. Ordered the pair from ebay, installed them, working, great. Turned it off to put it back together and noticed the heatsink was really hot on the repaired side. I found that the base voltage on both transistors was low. Swapped both transistors from the good side to the repaired side and its now fine. Put the new ones in the good side the and now the good side has got hot and all the voltages have dropped the same as they did when they were on the repaired side. Does anyone know where i can get a genuine pair of these transistors at a reasonable price? -- fruittool Any external giveaways as yo piracy? ground surface ? smudged printing or looks as though logo was stamped with a potatoe die? |
#6
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2SD2385 + 2SB1556 Transistors
On Thu, 25 Oct 2012 20:06:24 +0000, fruittool
wrote: I've just been done on ebay. Both output transistors on a Kenwood A-97 amplifier had blown. Ordered the pair from ebay, installed them, working, great. Turned it off to put it back together and noticed the heatsink was really hot on the repaired side. I found that the base voltage on both transistors was low. Swapped both transistors from the good side to the repaired side and its now fine. Put the new ones in the good side the and now the good side has got hot and all the voltages have dropped the same as they did when they were on the repaired side. Does anyone know where i can get a genuine pair of these transistors at a reasonable price? http://www.bdent.com/ only carries genuine semiconductor manufacturer's lines. Chuck |
#7
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2SD2385 + 2SB1556 Transistors
I tried using one of the new ones with an old complimentary [sic]
one from the good side and this caused a massive imbalance in the idle bias 1.4v for the good one and 0.6 for the suspect one. Can I assume from these voltages that the replacements are not Darlingtons? 0.6v is right for a single transistor and 1.2v (approximately double) for a Darlington? It sounds as if these aren't Darlingtons. Do you have a way to measure the current gain? It should be at least 1000 -- probably higher. |
#8
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2SD2385 + 2SB1556 Transistors
William Sommerwerck wrote: I tried using one of the new ones with an old complimentary [sic] one from the good side and this caused a massive imbalance in the idle bias 1.4v for the good one and 0.6 for the suspect one. Can I assume from these voltages that the replacements are not Darlingtons? 0.6v is right for a single transistor and 1.2v (approximately double) for a Darlington? It sounds as if these aren't Darlingtons. Do you have a way to measure the current gain? It should be at least 1000 -- probably higher. Pull one of the new transistors and check it with an ohm meter. If it tests like a single transistor, it is. |
#9
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On first examination there's nothing particularly suspect but, after checking what the proper markings would be, it turns out the gain classification (A, B or C) is missing on one and is the letter 'O' on the other. Another giveaway is the LOT number, it should be one number for the last digit of the year and one letter 'A' for January to 'L' for December. Both have three numbers and no letters. Regards |
#10
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2SD2385 + 2SB1556 Transistors
Do you have a way to measure the current gain?
It should be at least 1000 -- probably higher. Pull one of the new transistors and check it with an ohmeter. If it tests like a single transistor, it is. I assume you're referring to the base-emitter junction. |
#11
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2SD2385 + 2SB1556 Transistors
"fruittool" schreef in bericht ... Dave Platt;2949536 Wrote: I've just been done on ebay. Both output transistors on a Kenwood A-97- amplifier had blown. Ordered the pair from ebay, installed them, working, great. Turned it off to put it back together and noticed the heatsink was really hot on the repaired side. I found that the base voltage on both transistors was low. Swapped both transistors from the good side to the repaired side and its now fine. Put the new ones in the good side the and now the good side has got hot and all the voltages have dropped the same as they did when they were on the repaired side. Does anyone know where i can get a genuine pair of these transistors at a reasonable price?- What was the base-to-emitter voltage on the questionable transistors, when the amp is idling? How does it compare to the working parts? These parts (when genuine) seem to be Darlingstons, not just single transistors. You may have been sold a pair of mislabeled standard transistors instead - this would probably result in over-biasing and a high idle current. Or, possibly they're genuine parts, but have a higher beta than the ones for which the amp was spec'ed? The beta bin would be a one-character A, B, or C, possibly stamped on the lower left corner of the plastic. If that's the case, they might work OK with some adjustment to the idle/bias settings. TIP142/TIP147 *might* be acceptable substitutes although their gain seems lower. The design uses an STK350-030 ic to drive the output transistors. According to the service manual, at idle, the output from the driver ic to each transistor base should be around 1.2 volts. These new ones are causing that voltage to drop to around 0.6 - 0.8v, and this is with the bias adjustment full up. I tried using one of the new ones with an old complimentary one from the good side and this caused a massive imbalance in the idle bias 1.4v for the good one and 0.6 for the suspect one. Can i assume from these voltages that the replacement's are not darlingtons? 0.6v is right for a single transistor and 1.2v (approximately double) for a darlington? Regards -- fruittool No doubt you were sent single transistors instead of Darlingtons. The latter have two diode drops Vbe so 1.2V-1.4V instead of 0.6V-0.7V. If you did not find out already you could check using the diode tester of a common unimeter. petrus bitbyter |
#12
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2SD2385 + 2SB1556 Transistors
"fruittool" 'Phil Allison ** The fact they have a Vce of 100V as compared to the originals with 140V is far more of a worry. The BDV65C and BDV64C darlington pair is closer at 120V Vce. The OP can measure the +/- DC rails see if the total is more than 120V. I had this same concern, each rail is 52V. Your suggested parts seem closer but, would i have to change both pairs to keep the response of both channels identical? ** LOL - err, no. You really are a babe in the woods..... ..... Phil |
#13
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2SD2385 + 2SB1556 Transistors
"fruittool" TIP142/TIP147 *might* be acceptable substitutes although their gain seems lower. The design uses an STK350-030 ic to drive the output transistors. According to the service manual, at idle, the output from the driver ic to each transistor base should be around 1.2 volts. These new ones are causing that voltage to drop to around 0.6 - 0.8v, and this is with the bias adjustment full up. ** That will only make the transistors you have get very hot. I tried using one of the new ones with an old complimentary one from the good side and this caused a massive imbalance in the idle bias 1.4v for the good one and 0.6 for the suspect one. Can i assume from these voltages that the replacement's are not darlingtons? 0.6v is right for a single transistor and 1.2v (approximately double) for a darlington? ** Yep. Non darlington devices in that amp will not only run hot but deliver much less that full output power into a load. The fact is you simply have NO driver transistors unless darlingtons are fitted. ..... Phil |
#14
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2SD2385 + 2SB1556 Transistors
"William Sommer******" Pull one of the new transistors and check it with an ohmeter. If it tests like a single transistor, it is. I assume you're referring to the base-emitter junction. ** Darlington power transistors all have inbuilt diodes from collector to emitter - a very rare thing among regular transistors. The base emitter junction will also read higher than usual on an ohmmeter, the difference being more obvious with an analogue type on the ohms x1 range than with a DMM on "diode test". ..... Phil |
#15
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2SD2385 + 2SB1556 Transistors
"William Sommer******" It sounds as if these aren't Darlingtons. Do you have a way to measure the current gain? It should be at least 1000 -- probably higher. ** Most transistor checkers will not read correctly with power darlingtons. .... Phil |
#16
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2SD2385 + 2SB1556 Transistors
N_Cook wrote:
fruittool wrote in message ... I've just been done on ebay. Both output transistors on a Kenwood A-97 amplifier had blown. Ordered the pair from ebay, installed them, working, great. Turned it off to put it back together and noticed the heatsink was really hot on the repaired side. I found that the base voltage on both transistors was low. Swapped both transistors from the good side to the repaired side and its now fine. Put the new ones in the good side the and now the good side has got hot and all the voltages have dropped the same as they did when they were on the repaired side. Does anyone know where i can get a genuine pair of these transistors at a reasonable price? -- fruittool Any external giveaways as yo piracy? ground surface ? smudged printing or looks as though logo was stamped with a potatoe die? off ebay is a good clue they're not legit. |
#17
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2SD2385 + 2SB1556 Transistors
"Cydrome Leader" wrote in message ... N_Cook wrote: fruittool wrote in message ... I've just been done on ebay. Both output transistors on a Kenwood A-97 amplifier had blown. Ordered the pair from ebay, installed them, working, great. Turned it off to put it back together and noticed the heatsink was really hot on the repaired side. I found that the base voltage on both transistors was low. Swapped both transistors from the good side to the repaired side and its now fine. Put the new ones in the good side the and now the good side has got hot and all the voltages have dropped the same as they did when they were on the repaired side. Does anyone know where i can get a genuine pair of these transistors at a reasonable price? -- fruittool Any external giveaways as yo piracy? ground surface ? smudged printing or looks as though logo was stamped with a potatoe die? off ebay is a good clue they're not legit. Particularly if they ship from China, Hong Kong etc. Gareth. |
#18
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2SD2385 + 2SB1556 Transistors
"Gareth Magennis" "Cydrome Leader" off ebay is a good clue they're not legit. Particularly if they ship from China, Hong Kong etc. ** The only offer I see on Ebay for the 2SD2385/2SB1556 pair is from a UK dealer called "elmassari" in Surrey. He has a big range of spares for sale at low prices and some of it must be fakes. ..... Phil |
#19
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That's the one but the package is labeled ELECTRONIC COMPONENTS, SEMICONDUCTORS, PARTS, TRANSISTORS, INVERTERS, TRANSFORMERS | DALBANI and electronic component suppliers and distributors, Nikko Electronics for semiconductors, transistors, capacitors all major brands of spare and replacement parts. I found CHS - replacement remote controls, instruction manuals, audio & video accessories, electronic components & spare parts to have what i need. Anybody know anything about them? 2Sd2385 and 2Sb1556 To me, the pictures look genuine, the site looks a reasonable quality and has a uk landline number unlike the other site with it's 020 number. What do you guys think? Thanks, Ant |
#20
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2SD2385 + 2SB1556 Transistors
I found 'CHS - replacement remote controls, instruction manuals, audio & video accessories, electronic components & spare parts' (http://www.chsinteractive.co.uk/) to have what i need. Anybody know anything about them? Yes, Charles Hyde, I seem to recall, used to sell Tascam and other spares - I bought some from them. They were always ridiculously expensive, but they would definitely not knowingly be dealing with pirated parts. Gareth. |
#21
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2SD2385 + 2SB1556 Transistors
Will wonders never cease ? This place actually has a datasheet ! (they failed me so much I no longer bother, but at the end it said "PDF" so I got it)
http://www.datasheetcatalog.org/data...shiba/3250.pdf If you really cannot get them you can make Darlingtons, but I don't recommend it. However when you look at the internal diagram you see the the EB junction on a meter is not going to read like a Darlington because of the 100 ihm resistor across the EB junction of the output. You would only see the drop of the driver EB junction. Depending on your meter it might read 0.100 higher, but will not read 1.2 volts as you might expect. You are not ordering a million of these things, if the right part is a bit more expensive it is worth it. Like someone said B & D, but then I don't know where you are. If not in the US, dealing internationally can be a PITA. J |
#22
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2SD2385 + 2SB1556 Transistors
"fruittool" To me, the pictures look genuine, ** But you are an utter idiot. ..... Phil |
#23
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2SD2385 + 2SB1556 Transistors
http://www.datasheetcatalog.org/data...shiba/3250.pdf ** Shame the schem in the above omits the reverse diode across the C and E terminals. Easiest way to pick a power darlington with an ohm meter. ..... Phil |
#24
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2SD2385 + 2SB1556 Transistors
Actually it might not have one, there is no law.
With two resistors, a DVM and a 12 volt supply you can measure the hfe quite easily. That 100 ohm resistor is much more important, otherwise the Icex of the first transistor at the very least will always be applied to the base of the second transistor. The Ice leakage numbers for the whole device would look like germanium. J |
#25
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2SD2385 + 2SB1556 Transistors
Actually it might not have one, there is no law. ** Every darlington power transistor made has a reverse diode from C to E - it is part if the structure of the chip. All power mosfets have a similar diode. With two resistors, a DVM and a 12 volt supply you can measure the hfe quite easily. ** But you gotta be real quick or the device will cook. That 100 ohm resistor is much more important, otherwise the Icex of the first transistor at the very least will always be applied to the base of the second transistor. The Ice leakage numbers for the whole device would look like germanium. ** Hogwash. The 100ohm resistor is there to improve the switch off speed of the power transistor plus increase the breakdown voltage a little. Leakage current in the driver transistor is only a few microamps, at most, a current level the output device can barely amplify at all. ..... Phil |
#26
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2SD2385 + 2SB1556 Transistors
On 10/26/2012 7:21 AM, chuck wrote:
On Thu, 25 Oct 2012 20:06:24 +0000, fruittool wrote: I've just been done on ebay. Both output transistors on a Kenwood A-97 amplifier had blown. Ordered the pair from ebay, installed them, working, great. Turned it off to put it back together and noticed the heatsink was really hot on the repaired side. I found that the base voltage on both transistors was low. Swapped both transistors from the good side to the repaired side and its now fine. Put the new ones in the good side the and now the good side has got hot and all the voltages have dropped the same as they did when they were on the repaired side. Does anyone know where i can get a genuine pair of these transistors at a reasonable price? http://www.bdent.com/ only carries genuine semiconductor manufacturer's lines. Chuck http://www.pacparts.com/part.cfm |
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