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Old 16th Nov 2017, 10:55 am   #41
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Question A13TA Transistors-odd readings on DMM

Two of these are fitted in an ATX PSU used in a Dr.Dre Beatbox. The PSU isn't working, so, amongst other things, I decided to check the above components, which are in the primary circuit. On a cheap Chinese Tester they identify as NPN transistors having a hFE of 21, and Vf 614mV, which, to me seems reasonable enough, but on my M3800 DMM I get very odd readings, not like conventional Bipolar Power Transistors at all. I cannot find any data on these devices at all, ev3n if I put 2S in front of the numbers, but 2SC4242 transistors used in a similar ATX PSU (of which I've only seen a circuit diagram) have Vceo 400v, Ic7A, and are 40 watt TO220 devices, so I'd expect the (2S)A13TA to be similar. From what I can check, they appear to be OK, but I have in the past often had transistors check OK on testers only to fail when powered. Anyone have any further info. on these devices?
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Old 16th Nov 2017, 1:24 pm   #42
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Default Re: A13TA Transistors-odd readings on DMM

Any other identifying marks on them? Photo?
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Old 16th Nov 2017, 1:50 pm   #43
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Default Re: A13TA Transistors-odd readings on DMM

You say the Vf is 614mV. Is that the saturation voltage or Vbe. What readings do you get on your DMM? What is the package form factor of the devices?
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Old 16th Nov 2017, 2:27 pm   #44
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Default Re: A13TA Transistors-odd readings on DMM

These are TO-220 plastic power Transistors. All I know about the Vf is that 614mV was indicated on my Chinese Tester(One of those frequently advertised on eBay for about 10, which tests Caps., Resistors, Diodes & Transistors). With my DMM the voltage readings I get fall away rpidly within a minute or so of applying power to the OSU, so I can't answer the question, except tha 0.6v as is well known is thenormal Vbe for a silicon transistor.
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Old 16th Nov 2017, 2:49 pm   #45
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Default Re: A13TA Transistors-odd readings on DMM

If you're testing them in circuit, I wouldn't rely too much on any readings you get. The reason I asked about Vf vs. Vbe is that the minimum saturation voltage for a silicon Darlington pair (or Sziklai pair, for that matter) is the same.
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Old 16th Nov 2017, 11:01 pm   #46
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Default Re: A13TA Transistors-odd readings on DMM

These have been tested out of circuit, AG. My conclusion, having repeated the DMM and Chinese Instrument tests, is that the transistors are almost certainly OK, and the fault is elsewhere, probably electrolytic capacitors/
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Old 17th Nov 2017, 2:19 am   #47
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Default Re: A13TA Transistors-odd readings on DMM

If they are out of circuit connect collector of one to a small car type lamp and 12V.
With a 10K on the base dab it on 12V and see what happens.
If the lamp stays on and fades slowly it will be a MOSFET.
Dab the resistor on 0V to turn it off again.
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Old 17th Nov 2017, 11:28 am   #48
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Default Re: A13TA Transistors-odd readings on DMM

AFAIK they are conventional Bipolar power switching transistors, as shown on my Chinese tester, and from the circuit around them, but it may be worthwhile carrying out the test you suggest. This PSU has taken up a lot of time with, at the moment no result in sight, despite all the helpful suggestions from fellow forum members, for which, btw, many thanks, despite my tracing out much of the circuit, and replacing a known faulty, and several suspect components. This is galling to say the least! The circuit is similar to one on this website; www.pavouk.org It is on the second page near the bottom (200W ATX Power Supply)

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Old 18th Nov 2017, 11:19 am   #49
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Default Re: A13TA Transistors-odd readings on DMM

Having checked this PSU further yesterday, the circuit is indeed very similar to the one on the PavoUK site, and the A13TA devices are indeed bipolar NPN switching transistors, possibly made by Fairchild.
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Old 18th Nov 2017, 12:50 pm   #50
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Default Re: A13TA Transistors-odd readings on DMM

A further comment. The odd readings I was getting on my M3800DMM the other day was because the Battery (for once I had used a Zinc PP3 rather than an Alkaline one!) was virtually flat -it measured <4v on an analogue meter - The display was rather dim on the DMM, too, and I was Dim not to realise the battery was flat!. A replacement Alkaline PP3 restored correct operation and sensible readings!
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Old 19th Nov 2017, 6:16 pm   #51
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Default Re: A13TA Transistors-odd readings on DMM

Attached is a photo of the two A13TA Transistors on their Heatsink. I still havrn't been able to find any data on them. They have a stylised 'F' (Fairchild?) A13TA, and underneath J13009-2, the latter presumably either a batch or date code, printad on them. Package is To-220, connections, as viewed from the front, B-C-E
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Old 19th Nov 2017, 6:36 pm   #52
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Default Re: A13TA Transistors-odd readings on DMM

I think you have it the wrong way round. J13009-2 is the part number:

http://docs-europe.electrocomponents...6b80f9b073.pdf
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Old 19th Nov 2017, 8:09 pm   #53
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Default Re: A13TA Transistors-odd readings on DMM

Quote:
Originally Posted by 'LIVEWIRE?' View Post
The circuit is similar to one on this website; www.pavouk.org It is on the second page near the bottom (200W ATX Power Supply)
Hey there, have you poked around in the 'power good' circuit, which from the narrative, latches on only when there is no fault condition, enabling the main board?

The author says [from Czech to English auto-translation...[
''PowerGood

Mainboard needs "PowerGood" signal. When all output voltages goes to stable, then PowerGood signal goes to +5V (logical one). PowerGood signal is usually connected to the RESET signal
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Old 19th Nov 2017, 9:28 pm   #54
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Default Re: A13TA Transistors-odd readings on DMM

AG, thanks for that link. I just assumed that A13TA was the device type. I see also that the encapsulation is described as TO3P, not TO220. Sorry for misleading everyone on two counts! Al, this PSU is out of a Dr. Dre 'Beatbox'. The equivalent of tha 'Powergood' circuit has a trigger line which is supposed to be momentarily grounded when the on/off button is pressed. I can only check that by temporarily shorting the pin on the PSU PCB to earth. If the PSU, once I have refitted the components I've ben checking, fires up, then the fault is elsewhere. Oh well, at least I've learned a bit more about ATX PSUs than I knew before even if I've been looking in the wrong place for the fault!
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Old 20th Nov 2017, 10:23 am   #55
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As this is one of three threads I have running relating to the ATX PSU used in the Dr. Dre Beatbozx, could they not be merged, ossibly under the title of 'Dr, Dre Beatbox woes' or similar. This was my original thread, then there is one in the 'Sets & Parts wanted section requesting a PSU PCB for this equipment, plus another to do with what I wrongly assumed were A13TA transistors, since kindly identified by another member as being Fairchild FJA13009 devices. In each there are discussions as to what the devices are, and which may be faulty, etc., so a merger would bring all the Qs & As to gether under one heading, with a possible second thread in the 'Wanted' section for a replacement part. (Mods-do you agree?)
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Old 20th Nov 2017, 12:26 pm   #56
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Default Re: Dr Dre Beatbox problems

Threads merged as requested, some posts may be dislocated.
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Old 20th Nov 2017, 12:40 pm   #57
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Default Re: Dr Dre Beatbox problems

The data sheet for those transistors looks very much like the one for BUT11.
These come with either bare tabs or factory insulated ones.
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Old 21st Nov 2017, 12:13 pm   #58
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Default Re: Dr Dre Beatbox problems

As the J13009 transistors check out OK I won't be looking to replace them, but it's useful to know that the BUT11 is a possible replacement. I need to replace a 10 ohm SMD resistor that is O/C. This is in the base circuit of one of the J13009s, but the other thing I need to do is check on the main PCB for what may have caused the rectifier diode in the -7v supply line to fail s/c. After that, I may finally have a working PSU, and, hopefully a working Beatbox. If anyone else asks me if I can fix one, I'll be reluctant to take on another, due to the seeming lack of spare parts & service info. availability, plus all the problems this one has caused me!!
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Old 21st Nov 2017, 1:38 pm   #59
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Default Re: Dr Dre Beatbox problems

Ahhhh.... but now you're the go to guru on these things.......
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Old 21st Nov 2017, 1:40 pm   #60
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Default Re: Dr Dre Beatbox problems

You will need to find the fault that made the 10 ohm resistor go open circuit.
It may well go bang again if that fault is not fixed.
If the board looks a bit heat stressed around the diode just replace it with a bigger faster UF rated SMPSU diode.
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