Tuesday, August 30, 2011

Hum-Tech electronics one year Anniversary


 A quick view of my profile shows on user statistics that I have been a blogger since August 2010, That is exactly one year since I joined the world of blogging, and as we celebrate our first birth day here at Hum-tech electronics I wish to thank each one of you my dear friends and fellow technicians out there for your contributions,comments,feedback and words of encouragement..


As we share this birth day cake please allow me to call to your remembrance an African  proverb which says “ if you want to go fast, go alone.If you want to go far, Go together”, as technicians I think we can borrow a leaf from this saying….lets walk as a term GUYS……..

Wishing you all the best

Humphrey Kimathi




Tuesday, August 23, 2011

A Satisfied Customer Comes Back!!


 I received this email from one of my CRT Television repair course book Customer from Tanzania, and I was getting ready to find out where he needs my support in relation to his day to day repair works.

But as I continued reading down the email I realized this is a Satisfied customer who is coming back but this time not for any assistance as far his repair work is concerned but on how to add some flavors to his repair work by enjoying some of his favorites soft music in the background as he continue to enjoy his repair work.
Here is the Mail…..
I remember Amosi is one of my very first customers to buy my eBook, He came to me a few times at the early beginning and of late I have not heard from him but now I know why(The backlog is gone and his work bench is now cleared). So I expect very fast service delivery to his current customers. This will also definitely translate to increase in profit.

By the way dear Techs if you find your shop has many equipment laying on your shelves does not mean that your business is doing well….It could mean you are taking too long to diagnose and repair hence the backlog.

And if you are not careful you will find your shop full of equipment and you will have no room left even for you to sit comfortably. This will increase your stress levels and soon you find your output going down even more.

Another thing worthy to note is that in Tanzania English is not their First language but despite that Amosi seems to have read my book and understood it pretty well because I have written it in very simple English and numerous color photos to make the reader understand very easily.

Here is a clip by Emmy Kosgei.




Wishing you all happy repairing

Humphrey Kimathi
Author CRT television repair course




Friday, August 19, 2011

Mobile phone repair tips


 
Sometimes on your line of duty as a technician you may encounter a customer who brings to your shop equipment which maybe you don’t repair but insist that you check for them what could be wrong with their equipment.

Although I am not very experienced on mobile phone repair I usually get some customers who bring their phone to me for repair and usually if the problem is hardware related I undertake to repair it.

Mobile phone problem are frequently hardware related and if you are keen one can be able to make conclusions as to the faulty component even before opening the phone by listening to the customer complain.

Here is an example.

1.       Customer complain:

When I place a call the phone does not indicate when the phone has gone through. Only hear the other party if the phone is set to loudspeaker.
Check the ear piece with analogue/digital meter set in low resistance range. Should be around 30 ohm when okay.
Solution: Usually changing the earpiece (speaker) cures this kind of a problem.
2.       Customer complain:
 I can’t hear the other person. In that case when the phone is dialed the phone rings and when you receive the call. You can’t hear the other person.
Solution: ear piece fault see above. Again one can use loudspeaker if the phone is equipped with one.
Nb: remember the ear piece could be okay but there could be other factors which could be hindering it from functioning. Be very keen to do observations around the ear piece, gasket, connector parts, the housing itself. - is it completely closed (home). Any loose bolts or missing bolts which could make the ear piece not to connect fully to the circuit board? Also check the orientation of the ear piece in connection to the main board.
Note: The earpiece and buzzer (ringer) are different. Some mobile phone has earpiece and loudspeaker- in this case the loudspeaker is used also as buzzer (Polyphonic Ring Tones)
3.       Customer complain:
When I make a call the other person can’t hear me but I hear them
Solution: Check the microphone (mouth piece) is loose or faulty-usually replacing the mouthpiece cure this kind of problem.
4.       Customer complain:
The phone goes off often, switch on and off after a small shake.
Cause: battery bad or shorted or battery connector loose.
Solution: change the battery/ Check the battery connector is firm.

Tip: Dust is one of the main killer of electronic gadgets and mobile phones is not excepted and therefore before you start suspecting component failure on mobile phone please be sure to do thorough cleaning of the PCB board with medicinal spirits and dry the board well with hair blower or hot air (this usually solve 30% of mobile phone problems)

That’s all for today guys

See you in our next class



Monday, August 15, 2011

REPAIR TV REPORT PARS GRUNDIG 21" COLOR TV PART –Dead part2

In the first part of this repair report by Mr. Beh, he promised to come back with his final report of what he did next to the Grundig 21” Tv which refused to have high voltage even after replacing the fly back with a new one.

No doubt Mr. Beh is back with his final report on this repair …

Mr. Beh tells us we are listening…….. After I changed the fbt of this Television with a new one I expected the Tv to start working but the TV did not work and therefore I did not have high voltage yet.
 
This TV has an ic on the drive circuit and I decided to Google it and see what is it all about, the reference of this ic was TDA8140, after searching the net for this ic this is what I got.
The TDA 8140 is a monolithic integrated circuit designed to drive the horizontal deflection power transistor। And here is the application circuit for the same.

From the datasheet above you can see no doubt this is a very important component as far as horizontal deflection circuit is concerned because it is actually the driver circuit.
So I decided to change it and this time the TV has high voltage and I was happy but wait a moment, the picture came up but with a vertical line at the middle.

I started testing components on the same circuit and I found an electro cap in same circuit which was not good according to my meter and after replacing it the white line disappeared.


The Television is now happy and ready for collection by the customer.
Thank you guys.
God bless You
By Mr. Beh.... An Electronics repairer based at Tehran in Iran. 

Monday, August 8, 2011

REPAIR REPORT OF PARS GRUNDIG COLOR TV 21” MODEL 5593-DEAD


This article is brought to you by Mr. Beh. An Electronics repairer based at Tehran in Iran.

Initial facts:
The estimated age of this Television is around 12 years of continuous service, No circuit found over the internet.
First I have to tell this TV set was rejected by authorized repair center and brought to me Completely dead with no sign of life, After blowing the inside I checked the Big capacitor by analogue meter set on dc mode 300 v dc
My voltmeter confirms that the 300 volt dc is reaching to the pin of the main capacitor (The red probe to the Positive side of capacitor and black probe to the negative side of the BIG filter cap).
With this I concluded that that all components before the main capacitor like bridge rectifier on /off switch, AC cord are ok and therefore not considered for any further testing.
I checked pin no 6 of regulator ic this is TDA4605 ( by goggling I found the diagram of the ic and the Vcc of this ic that was pin no 6) the red probe of the meter was on the pin 6 and the black probe the negative pin of the Big filter capacitor.
My meter read nothing. Zero volts. Checking the pins of this ic and all surrounding component I found out that there were many cold joints in the low power supply area. I took time and re- soldered them all again.
After that I powered the set and checked pin no 6 of regulator ic and Yes! I got about 11 v dc in V cc pin of ic and is within tolerance. This means the set is getting all the important voltages but to my surprise still TV has no sign of life.
Then is decided to check the secondary side of smps. With my analogue meter I checked the voltages coming out of the smps. This TV has 5V output from the transformer and 5V Schottky diodes, by putting the red probe to the negative (Cathode) side of diodes and black probe to cold ground of the Television.
I checked them all one by one, the voltages were within tolerance and are ok and I was happy up to here. In old CRT TV, usually there are two components that bring problems.
1 HORIZONTAL OUT PUT TRANSISOR (H.O.T)
2 FLY BACK TRANSFORMERS
First I checked the H.O.T by putting my meter on ohm mode x10k (H.O.T in this set is BU508D). D means a diode also is installed in the transistor compartment
And the shape of pins from left to right when the face of transistor is up is B.C. E .And by comparing the reading of meter with new healthy transistor I put ok stamp on this H.O.T of this TV. But what else can cause this problem? The only card remaining is now the fly back transformer?
To test the fly back I used my home made fly back tester which was on my work bench, I checked the pins of this transformer comparing with a good fbt and I concluded that trans former(FBT) is not ok because checker showed two L.E.D were lighted.
Below you can see assembled homemade fly back transformer and expected result from a good fly back transformer (all L.E.Ds) are ON.
I changed with one I had in my salvage stock, After replacing the fly back still there was no high voltage ?...having used my last card I took a break…
See you on the next and last part of this intriguing repair experience
God bless all repairer
Beh

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