Saturday, March 25, 2017

Sony DVD model DAV-TZ200 Home theatre system “no disc” symptoms repaired.

A friend of mine brought to me his home theatre to me to check it out, the initial complaint was that it was not able to read disc.
Upon receiving it on my workbench I pressed the power button and it came up well...




Friday, March 10, 2017

Understanding the CRT television regulation control circuit

Sometimes I get question from my customers where they complain the B+ of the CRT television is higher than expected.

In those cases I always refer them to the feedback circuits. In this article I am going to highlight a few things about this circuit.

First let me point out that all switch mode supply (S.M.P.S) tend to increase more and more after startup.

Therefore engineers decided to come up with a solution and that is when they introduced the regulation circuit.

Below you can see components involved in regulation in the circuit diagram below.


Monday, February 27, 2017

Connecting speakers in series and in parallel

When connecting an amplifier to a speaker it is important to match the impedance of the amplifier to the speaker for maximum power transfer:

On the circuit below we have an 8 ohm amplifier connected to two 4 ohms speaker in series to get 8 ohms (4+4) and therefore the amplifier impedance is equal to the speaker impedance.

If you don’t observe this principle then you will overload the amplifier and eventually it will blow.
  

Friday, February 17, 2017

Simple test for Cathode ray tube (CRT) bad or not.

To do this test, be sure you have the screen voltage presence and the heater is lighted and HV is present.



Friday, February 3, 2017

China TV (La76931) No raster, picture or sound

Clifford May Johannesburg South Africa
Hi Humphrey,
I've got a problem with this TV as you will see on the schematic I've got all voltage except 5volt on n552. 12v is ok on n551 but no 5volt coming out of n552. It gives me 1.2volt. I also changed transistor n552 but still the same. I desperately need your help please. Thanks in advance.
Kind Regards
Clifford



Monday, January 23, 2017

M-TECH DVB-T2 decoder dead now repaired

A friend of mine called me to pass-by his place to check out his Decoder which was faulty, I passed by and the decoder was dead as dodo.

Usually in electronics dead symptoms are mostly caused by power supply, therefore I suspected problem with the power supply.

I did not have my tools with me and therefore I did not open the decoder on site, back to my workshop I opened it and the first thing I did was scanning for any sign of stress (blackened area or burnt components).

Everything looked good and I was about to pull my digital meter to do some voltage testing when I noted a capacitor on the secondary side of the power supply which had it top slightly swollen.

As I said previously and I repeat again, any capacitor with swollen top is usually faulty, this usually happens when the working voltage of the capacitor is exceeded.


Wednesday, January 18, 2017

MK-328 Multi component tester (Transistors NPN PNP MOS, Capacitor ESR, Inductance, Resistor, diodes)

This meter is an intelligent semiconductor device analyzer, it can measure most of the diodes, bipolar
Transistors, Junction/MOS FETs and low power thyristors. It automatically identifies the type of devices and Pinouts, measures the current gain HFE, gate threshold and FET junction capacitance, a typical application is to pair two transistors or identify an unknown SMD device.
Test clips can be connected any way round, the
Pinout can be identified and displayed on screen vs. test clip numbers. Beside the semiconductor device analyzer, this meter can also work as a RLC/ESR meter, the RLC/ESR accuracy may not be able to compete with the professional one, but it definitely meets the needs for most of the applications. A 9V battery (part number 6F22) is used for this meter.




Orion HT800HC Dead as a Dodo

Hello Humphrey! Did you write the article on the Orion HT800HC? I have exactly the same problem with an Orion HT800HC and being a hobb...