Thursday, October 28, 2010

AMPEX AUDIO AMPLIFIER REPAIRED


The owner of this amp told me that the last moment of this amp was that he saw smoke oozing out from the amplifier and therefore I did not intend to apply power again to the amp lest I do more damage inside.

After opening the amp I went straight to test the transformer to see if it is okay…sure it has survived the ordeal.

Next I scanned around the circuit board and I noticed one component which has a catastrophic failure-as you know you don’t need to test a component with this kind of failure. Your eyes are good enough test equipment.



The two components happened to be TDA2030A: they were sharing the same heat sink so I removed them from the circuit together.

I applied power to the amp and I noticed the output voltage is still too low, the transformer is rated(13x2) therefore I was expecting around 18 vdc(13X1.414) but was too low.

So I suspected there must be another shorted component not yet picked up.

I switched off the power and touched on the components around the circuit looking for any component which is hotter than usual and I bumped on another component (i.c) which was very hot to my finger.



This must be the culprit, after checking it I found it was also a TDA2030A.

I removed it from the circuit and the voltage went up to (+-18 vdc) and I concluded that there is no more shorted component on the circuit.

The underside of the board has three darkened area where the i.c were installed which was further evidence that they must have been shorted.



I replaced the three TDA2030A and the amplifier came back to life.

Afterwards I searched for the datasheet of this i.c TDA2030A to check for its specifications and I noted that it is a 14 Watts HI-FI- audio amplifier and uses dual VCC(+-) hence why I was getting(+-18 vdc) on my meter.

I also found that it has other applications and I was particularly interested on its application as a crossover filter, a complete 3-way 60 Watt active loudspeaker system as shown in the diagram below.




I am a fun of do it yourself (D.I.Y) and this is definitely my next project thanks to Contek Microelectronics Co, Ltd.

Thank you guys

Let meet in the next class

Saturday, October 16, 2010

LG DVD. Disc spins at high speed but no audio no video.

This LG DVD was brought in by a friend of mine, it was not his so not much history of the problem but the owner has told him that the DVD has never gone to any other technician.

It didn’t take long before I realized that this was not true, usually equipment from other technician referred to another has its challenges especially if the one handling it before was not a professional.

Before opening I powered it up and it came up pretty well, the disc is spinning at high speed but no audio or video coming out.

I took some time observing the DVD and I noticed that the track count is also stuck, I opened the set and tried to push the pickup to the outer side..Alas the pickup was very hard to move, it should move softly either way.

I checked the sled motor by applying some dc voltage to it and rotated very well minus the load of course. Never apply power to the CD motor in circuit. You might end up doing more harm to the circuit.

With this I concluded that the sled motor was health. Then I applied power to the set with the pick up on the out lane. To my amazement the pick is supposed to move toward the center but this time it stayed at the same place (stuck).

I checked the gears and all seemed ok to my judgment. So what next….. After careful checking I realized the gear is not locking up well. Someone might have opened the set before and did not return the gears correctly?

I suspected previous repair because one bolt was also missing which hold the Loader mechanism. Remember the owner claimed that the set was never opened before.

So always be careful to check if the unit was ever opened before because this will allow you to think outside the box. Always be careful with unit which had previous repairs by other people.

I believe the previous technician repaired the machine but only missed when it came to re-assembling the machine, as a technician please note that there is no school to teach you how to open and close the equipment you will be working on and therefore it is up to the technician to be keen when opening especially new machine because when closing up you will be doing exactly the opposite of what you did when opening.

So I reinstalled the gears correctly and the DVD started working like new.

Thursday, October 14, 2010

Thank you for your support

Hum-tech electronics wish to thank all our visitors to electronics repair made easy for visiting us, in our mother language we say” ASANTE SANA” please feel free to give your comments, and suggestion that you think you as a consumer need to be added to our site. Also if there is any tech. who wishes to share his experience with us we are ready like yesterday to publish his article.


Two months down the road after the birth of hum-tech electronics we have registered over 2000 Visitors and still counting.

Wednesday, October 13, 2010

meet my former college mate

i meet one of my former college mate and i was interested to know how he has been fairing since we left college at  K.C.I.T.I some years back and this what he has been up to:-

The beuty with electronics is that we don't have to be employed by others to earn a living, one can choose if you want to go alone or work for someone. or even do it part time.

i wish him all the best

Saturday, October 9, 2010

JVC 14'' DEAD AFTER A VOLTAGE SURGE FROM A GENERATOR

In the last article I described to those new to electronics or do it yourself on how to handle a case of electronics equipment using S.M.P.S. which has succumbed to power surge or high voltage.


In this article I encountered a real life situation from a customer who brought in his JVC TV for repairs.


The customer complains was that the TV was blown by high voltage from a generator.


I opened the set and scanned around the primary side of the power supply and found the main filter capacitor was bulging out.


I replaced it together with the control chip (str-G6653) which almost always goes when there is power surge.






After replacing the two components the set came up but no color (Picture was black and while) with some very thin lines across the screen.


I hit the set softly with my bare hands and the color came on but intermittent.


Then I concluded that the set has dry joints too. I soldered all the suspect areas starting from the RGB neck circuit board.








 and Component around the main ic (Jungle) and the color came back to normal.








Later I went to his house to check on the root cause of the problem which was the generator.


You know in electronics it is not wise to just replace the faulty components, always look for the root cause of the problem, it may be dry joints or Capacitors that have developed high ESR and therefore if you only replace the faulty component chances are high for call back.




This will affect your reputation and also waste more of your time, it is better to do your repair pretty well and that customer bring to you more customers by referrals than waiting for the same machine to come again after some time..It is simply not fair to your customers.


The generator was switched on and after measuring the output voltage was found to be at 330 Vac.


But why did the Main Capacitor which is rated 400Volts blow up? This is because you meter measure R.M.S (root mean Square) of the AC and not the peak.


To get the peak Voltage you have to multiply your meter reading (AC) by 1.414.( Therefore 330 X 1.414= 466 vdc)


Way above the maximum voltage rated for the main Capacitor.


So I adjusted the Generator Voltage to 220 Vac and went back to my workshop to serve other customers.


Thank you guys


Stay safe