Tuesday, August 2, 2011

Testing integrated circuit (i.c)

I have received several emails from techs who come to me for some guidance in relation to at what point should one suspect an ic is faulty. In this article I wish to shed some light on this issue in relation to CRT television. (Of course you can use the same knowledge in other equipment using ics) 

In CRT Television we have several ics like Audio I.C, Vertical ic, RGB amplifier ic, control ic in the power supply and lastly the jungle and micro processor ic.
The latter ics are quite expensive and therefore it is very important to very sure that indeed it is the ic which is faulty and not related components causing the problem. 
The word integrated in Basic English means included there in. Such as active components like transistors and passive components like resistors, capacitors in order for it to function.
So in I.C like the micro processor or jungle ic expect many components both active and passive which form circuit with different functions within that particular ic.
So one clue that an ic is bad is function failure, Take for example the micro processor part of the circuit which produces tuning pulses for channel selection in CRT television. If this particular circuit fails then you will find the TV is not able to do channel auto searching.
If you get this symptom and you find the entire external component associated with turning are OK, then you can conclude that the micro has failed partially because you will find sometimes other functions of the micro will be okay.
If you find NO function of the micro is working, then first check if the micro is getting power. Power supply is very important for any ic/circuit to work and therefore should always be checked to see if it is present and correct value.
Another common occurrence on these ic is actually dry joints on the components around it and also actual ic pins.
Sometimes a technician can change the whole ic when actually the problem was dry joints. So when you replace the ic its like you have re-soldered and hence if the TV work you will imagine that actually it was the ic faults while it was just dry joints problem.
This will waste your time and also lower your profit margin, from my experience I have seen these main ic(the micro and jungle ic) are quite reliable and highly protected from static discharge and power surges and therefore should be last on your suspect lists.
Below you can see a diagram of a TV micro, before you replace it consider checking the fuses around this ic, you never know they were fast enough to open to protect the micro and changing only one of them can cure the problem.


 
Tip
One good symptom of a bad ic is that they usually get HOT and also the VCC voltage goes down(Nb you expect 5 volts but you are getting 2volts
 
To learn more on how to troubleshoot and repair CRT television like a professional click the link below…
Wishing you all the best
Humphrey Kimathi
Author CRT Television repair course

6 comments:

  1. Hi Humprey,

    i have a aiwa tv-an1410nh model, it has no power, led indicator infront of tv does not lit. initial checks are; 1) 309 volts at filter capacitor in primary supply of SMPS 2) 15.3 volts at pin 4 (VccIN) of STR-F6654 off-line quasi resonant flyback switching regulators 3) 117 volts @ D807, 14.5 volts @ D808, and 20.8 volts @ D809 of the secondary supply 4) 117 volts @ collector pin of HOT (Q601) transistor... with all this initial checks, what further test do i need to do in order to arrive at a possible circuit/section that is causing a no power problem?

    Thanks,

    tol

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  2. Hi, very good initial test...you have not mentioned about the 5volts source..very important for micro..reset, power ON led..so i suggested you check this source thoroughly.

    Kind regards Humphrey

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  3. Sir,

    i check the 5 volts source responsible for the micro-computer control and led driver and found out that the zener diode, (MTZJ5.6B) is shorted when tested out of circuit. the cathode side of this zener outputs a 5.6 volts which is then fed at the base of 2SD1207T 5V REG transistor, that's why it has no output voltage at its emitter pin which supplies the Vcc pin of the micro-computer control ic and several other components that relies on this 5 volts source... this transistor is ok when tested out of circuit as well all the surrounding components that are connected to this transistor. i'm sending you the schematic diagram of this tv model. i'm going to replace this zener diode and will give you and update once it's done... thank's

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  4. Sure keep me posted on this please. regards Humphrey

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  5. Sir Humprey,

    sorry for the late reply... so far i've replaced the 5.6 zener diode and the led indicator lits back again. but the tv does not power on, and i've found a transistor which must output around 15 volts that goes directly to the 9 volt voltage regulator (KIA7809PI). i've already replaced the 2SB892 transistor but still it only outputs around 0.1-0.2 volts at it's collector pin... i also checked the surrounding components around this transistor and IC, and they are within their normal specifications. so what else do i need to check? thanks


    Best Regards,

    Lito

    ReplyDelete
  6. Hi lito, This transistor 2SB892 output feeds both the vertical circuit and horizontal drive circuit..if its output is low mean either of the two source is has a short..check your ebook on page 44 and 47 for more info.

    regards Humphrey

    ReplyDelete