Kenwood CS-4135 Oscilloscope defective transistor - Page 1
Forum section: electronics / repair

author: stevengendron
author_rank: Contributor
timestamp: November 03, 2018, 07:57:35 pm
content: Hi ! I have a defective oscilloscope Here. Kenwood CS-4135.The channel 1 is defective so I took out the input board. I tested the first transistor on the channel input circuit and it's defective.However, I don't know what part to order.I found a service manual for a CS-4135A but it does not seems to be the same thing.The part number on the board is Q151Here's a picture of the transistor.Anybody knows what part number I should order ?Thanks

author: anachrocomputer
author_rank: Regular Contributor
timestamp: November 03, 2018, 08:21:44 pm
content: It's common for transistor markings to omit the prefix "2S", so this could be a 2SA114. A quick search for that part number reveals a few images that show a similar transistor in a similar package.

author: glarsson
author_rank: Frequent Contributor
timestamp: November 03, 2018, 08:57:42 pm
content: True, but 2SA114 is a germanium transistor and the picture shows a case not typical for a germanium transistor.

author: tautech
author_rank: Super Contributor
timestamp: November 03, 2018, 09:16:12 pm
content: Quote from: stevengendron on November 03, 2018, 07:57:35 pmTypically a FET.So looking harder:J = P-channel fet K = N-channel fetRead more at:http://www.epanorama.net/documents/markings/semiconductor_markings.html

author: Chris56000
author_rank: Frequent Contributor
timestamp: November 04, 2018, 12:29:56 am
content: Hi!That's a "Digital Transistor" you have there, it's a DTA114 PNP Digital Transistor – there were used by the dozens in 1970s and 1980s Japanese made VCRs, and are made in groups A, B or C or X, Y or Z according to the values of their internal series base and base/emitter resistors. The NPN type is DTC114 marked "C114" and a suffix letter. There are also surface–mount SOT–23 versions of these things, but data is fairly readily available!You won't get the normal 0.6 – 0.7V b/e drop with these – they were designed to be directly connected to chip outputs, etc., without an intervening series resistor, for this reason a lot of testers can't identify them correctly but I believe the Peak Atlas can!Going back to your scope, if the base is pulled low the collector voltage of the DTA114 you showed us should come up to the emitter voltage (I've not looked at the circuit yet but I'm assuming it's connected as upside–down PNP with emitter going up towards an LT+ point and collector down towards chassis–earth/0V)Hope this helps!Chris Williams

author: coromonadalix
author_rank: Super Contributor
timestamp: November 04, 2018, 08:41:05 am
content: They where use as switch transistors / logic inverters / muting circuits etc ...ftp://ftp.tvnalber.com/DTA114.pdfSee the resistors in it ...

author: mikerj
author_rank: Super Contributor
timestamp: November 04, 2018, 05:55:54 pm
content: Quote from: coromonadalix on November 04, 2018, 08:41:05 amYep, they were very common before low voltage MOSFETs started to appear. You can emulate the function with a jellybean NPN part and a couple of 1/8W resistors if you don't have a replacement.

author: mzacharias
author_rank: Frequent Contributor
timestamp: November 07, 2018, 03:35:01 pm
content: By the way - the transistor shown is almost certainly good. With two multimeters you can check it.One meter measuring resistance Emitter-Collector.The other meter on diode check function, connect that meter so as to forward bias the Emitter-Base junction.Meter number one should go LOW resistance when the Emitter-Base is forward biased.