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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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#1
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Horizontal output question
This may seem to be a stupid question to many of you, but here it goes
- I checked a horizontal output transistor with my fluke (diode check). The transistor is an NTE2353. It has a built in damper diode. Since I don't know how this diode is fixed in the transistor, I'm not sure if I'm getting accurate results. I get normal voltage drop between the base and collector. I read dead short between base and emitter (both ways). Regardless of having a damper diode, I shouldn't get this reading on a good transistor, right? I just want to be sure before buying a repalcement. Thanks group. |
#2
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Horizontal output question
"Golf" wrote in message oups.com... This may seem to be a stupid question to many of you, but here it goes - I checked a horizontal output transistor with my fluke (diode check). The transistor is an NTE2353. It has a built in damper diode. Since I don't know how this diode is fixed in the transistor, I'm not sure if I'm getting accurate results. I get normal voltage drop between the base and collector. I read dead short between base and emitter (both ways). Regardless of having a damper diode, I shouldn't get this reading on a good transistor, right? I just want to be sure before buying a repalcement. Thanks group. Many horizontal output transistors have a built in B-E resistor of 30 ohms or so. A dead short means it is bad. David |
#3
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Horizontal output question
In article ,
"David" wrote: "Golf" wrote in message oups.com... This may seem to be a stupid question to many of you, but here it goes - I checked a horizontal output transistor with my fluke (diode check). The transistor is an NTE2353. It has a built in damper diode. Since I don't know how this diode is fixed in the transistor, I'm not sure if I'm getting accurate results. I get normal voltage drop between the base and collector. I read dead short between base and emitter (both ways). Regardless of having a damper diode, I shouldn't get this reading on a good transistor, right? I just want to be sure before buying a repalcement. Thanks group. Many horizontal output transistors have a built in B-E resistor of 30 ohms or so. A dead short means it is bad. David Would a 30 ohm resistor look like a "short" to a fluke set on the diode check function, as the OP said? |
#4
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Horizontal output question
On Jul 7, 11:44 am, "David" wrote:
"Golf" wrote in message oups.com... This may seem to be a stupid question to many of you, but here it goes - I checked a horizontal output transistor with my fluke (diode check). The transistor is an NTE2353. It has a built in damper diode. Since I don't know how this diode is fixed in the transistor, I'm not sure if I'm getting accurate results. I get normal voltage drop between the base and collector. I read dead short between base and emitter (both ways). Regardless of having a damper diode, I shouldn't get this reading on a good transistor, right? I just want to be sure before buying a repalcement. Thanks group. Many horizontal output transistors have a built in B-E resistor of 30 ohms or so. A dead short means it is bad. David- Hide quoted text - - Show quoted text - Thanks. I did check and I read 36 ohms between B and E. But as I said, doing a diode check, I read dead short both directions. Shouldn't a resistance reading only be able to be taken with common lead on emitter if transistor (NPN) is good? |
#5
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Horizontal output question
Am 07.07.07 13.06 schrieb Golf:
On Jul 7, 11:44 am, "David" wrote: "Golf" wrote in message oups.com... This may seem to be a stupid question to many of you, but here it goes - I checked a horizontal output transistor with my fluke (diode check). The transistor is an NTE2353. It has a built in damper diode. Since I don't know how this diode is fixed in the transistor, I'm not sure if I'm getting accurate results. I get normal voltage drop between the base and collector. I read dead short between base and emitter (both ways). Regardless of having a damper diode, I shouldn't get this reading on a good transistor, right? I just want to be sure before buying a repalcement. Thanks group. Many horizontal output transistors have a built in B-E resistor of 30 ohms or so. A dead short means it is bad. David- Hide quoted text - - Show quoted text - Thanks. I did check and I read 36 ohms between B and E. But as I said, doing a diode check, I read dead short both directions. Shouldn't a resistance reading only be able to be taken with common lead on emitter if transistor (NPN) is good? The damper diode is connected between C and E (which usually is ground), with its anode connected to E and its cathode to the transistors C. So if the diode is still good and your transistor's C-E path is not shorted, then in diode test mode you should only get a reading with (+) of your DMM connected to the transistor's E and (-) touching its C. In respect of the 36Ohm base resistor, this value is too low for your DMM's diode test to tell you anything reliable. But still reading the 36 Ohm means your B-E path is not shorted, which is rather unlikely anyway. They usually short C-E, or quite occasionally C-B. From what you wrote so far, I'd conclude that the transistor is still OK. But you could do a quick test with a 12V source. f.e. car battery, a 10W light bulb (dome- or number plate light), a few connector wires with crocodile clips and a resistor some 220 Ohm to limit the base current. If you can turn on and off the light by touching releasing the base with the resistor, the LOT should be fine. Also reverse polarity on C-E to test the diode. In this case the bulb should be on constantly. |
#6
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Horizontal output question
On Jul 7, 1:57 pm, Wolfi wrote:
Am 07.07.07 13.06 schrieb Golf: On Jul 7, 11:44 am, "David" wrote: "Golf" wrote in message groups.com... This may seem to be a stupid question to many of you, but here it goes - I checked a horizontal output transistor with my fluke (diode check). The transistor is an NTE2353. It has a built in damper diode. Since I don't know how this diode is fixed in the transistor, I'm not sure if I'm getting accurate results. I get normal voltage drop between the base and collector. I read dead short between base and emitter (both ways). Regardless of having a damper diode, I shouldn't get this reading on a good transistor, right? I just want to be sure before buying a repalcement. Thanks group. Many horizontal output transistors have a built in B-E resistor of 30 ohms or so. A dead short means it is bad. David- Hide quoted text - - Show quoted text - Thanks. I did check and I read 36 ohms between B and E. But as I said, doing a diode check, I read dead short both directions. Shouldn't a resistance reading only be able to be taken with common lead on emitter if transistor (NPN) is good? The damper diode is connected between C and E (which usually is ground), with its anode connected to E and its cathode to the transistors C. So if the diode is still good and your transistor's C-E path is not shorted, then in diode test mode you should only get a reading with (+) of your DMM connected to the transistor's E and (-) touching its C. In respect of the 36Ohm base resistor, this value is too low for your DMM's diode test to tell you anything reliable. But still reading the 36 Ohm means your B-E path is not shorted, which is rather unlikely anyway. They usually short C-E, or quite occasionally C-B. From what you wrote so far, I'd conclude that the transistor is still OK. But you could do a quick test with a 12V source. f.e. car battery, a 10W light bulb (dome- or number plate light), a few connector wires with crocodile clips and a resistor some 220 Ohm to limit the base current. If you can turn on and off the light by touching releasing the base with the resistor, the LOT should be fine. Also reverse polarity on C-E to test the diode. In this case the bulb should be on constantly.- Hide quoted text - - Show quoted text - I did a similiar test. Only without light bulb. Properly biased the trans. It worked. Removed the base voltage, and it still conducted with the same forward voltage across the emitter and collector. My conclusion, since I can't turn off the transistor by removing base voltage, it's shot. By the way, I did have to replace another NPN in the SMPS of this same chassis. The Base and Emitter were shorted. The Emitter to Collector checked good. Thank you to all that responded. I wanted to be sure of what I already suspected, just the damper diode made me question if my test results were accurate. If ya'll agree with my findings, I am going to go ahead and order the replacement HOT. Thanks again group. |
#7
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Horizontal output question
Golf wrote:
I did a similiar test. Only without light bulb. Properly biased the trans. It worked. Removed the base voltage, and it still conducted with the same forward voltage across the emitter and collector. My conclusion, since I can't turn off the transistor by removing base voltage, it's shot. I always feel safer shorting base to emitter to shut off a BJT. -- Postulate a group whose intent is to destroy the United States from within via anarchy and bankruptcy. The actions of the United States Congress are completely consistent with the actions one would predict from such a group. |
#8
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Horizontal output question
clifto writes:
Golf wrote: I did a similiar test. Only without light bulb. Properly biased the trans. It worked. Removed the base voltage, and it still conducted with the same forward voltage across the emitter and collector. My conclusion, since I can't turn off the transistor by removing base voltage, it's shot. I always feel safer shorting base to emitter to shut off a BJT. That B-E resistor really should be low enough to do that. --- sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/ Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/ +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html Important: Anything sent to the email address in the message header above is ignored unless my full name AND either lasers or electronics is included in the subject line. Or, you can contact me via the Feedback Form in the FAQs. |
#9
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Horizontal output question
Sam Goldwasser wrote:
clifto writes: Golf wrote: I did a similiar test. Only without light bulb. Properly biased the trans. It worked. Removed the base voltage, and it still conducted with the same forward voltage across the emitter and collector. My conclusion, since I can't turn off the transistor by removing base voltage, it's shot. I always feel safer shorting base to emitter to shut off a BJT. That B-E resistor really should be low enough to do that. True, but when I don't rely on extensive knowledge of the circuit under test, I find fewer ways to outsmart myself. -- Postulate a group whose intent is to destroy the United States from within via anarchy and bankruptcy. The actions of the United States Congress are completely consistent with the actions one would predict from such a group. |
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