TVC LCD AMSTRAD 26” REPAIR CARD

Brand : Amstrad   26”

Model : T2712                                                                               Roberto Salerno

Schematic : not found                                     

Fault : A hint of brightness on switch on  then nothing. 


 When switched on at main I had an indication of brightness; then nothing but the standby  led  flashing  in continuation. Obviously there is no audio.  

These  Amstrad power supplies are well known to  easily  "give up"  after some  time. 

After removing  the  protection cover  I see that the power supply is a   AUO type, a typical instrument adapt for power supply  on  AUO Optronic  LCD panels. 

I  immediately notice  a swelling on the CAP  C355 (1000 F-25V-105°). 

I dislodge  the Power Supply from it's seat  removing the four screws and connectors attached to it.  I replace the CAP with a  higher operating  tension one,  precisely  105°C. 

On these power supplys  it is always advisable to check  the weldings on the various connectors,  I fresh solder any  suspicious ones...…

 I also  replace without delay any suspicious CAPS.  

I reassemble  all and give power to the unit,   after a few seconds of flashing  the  front led (preliminary  bootup phase ) switches on as usual. 

 If it is necessary to replace the power supply  on these Amstrad LCD  instruments  you must choose one with the correct  tension, in particular  those going to the panel. 

 So  if we have a AUO  panel  we must use a  AUO Power Supply  and  if we have a LG panel, we must use a LG power supply  etc...etc.... 

Visually, these power supplys are very similar  but it is dangerous to substitute them.  In particular , if a  LG type power supply  is inserted on a AUO  panel , we  seriously risk  damaging  the panel in a  irreparable way. After keeping it on trial basis I had the unit restored to full operation. 

 

Schaub Lorenz DVD Player REPAIR CARD

Brand: Schaub Lorenz

Model: SL 27900

Schematic: not found

Fault: no disc reading                                                                             Riccardo Omage

This DVD reader is a rather up-market brand, but nowadays with most electronic devices arriving from China, at a low cost, even if it is almost new, there it is on my work bench for repair.

On the initial display, humming bars appear, they disappear after a few seconds.

The Dvd disc loads regularly but the disc motor is running slow speed, at the same time the humming bars reappear also a loud humming noise. The disc stops and “no disc“ appears.

On all the secondary power supply voltages tensions in output, we find a ripple as can be seen in the photo, it can be found in more evidence on 5V and on 3,3V rather than on 12V.

This ripple has a main A.C. frequency, therefore I replace the CAP 33uF-400V (C1) on the primary side, note that it filters the tension in output from the Graetz bridge: I obtain a fully working unit.

Please note that the faulty CAP did not appear to be swollen or even leaky, so after having dismantled the unit no visual faults appeared.

It was the E.S.R. tester that revealed the faulty CAP (completely opened).

I was really surprised as it is not often that I find a CAP in this particular condition.

Considering the noise hum, even if it is irregular it seems to me to be an “old” fault found in a modern device; but browsing through other technicians repair cards and reading the pages of “Us Repairers”, I have come to the conclusion that CAPS sold nowadays are not what they used to be. Particularly the one found in this position, I have very rarely found it faulty, as for the others, well they started requiring replacement after five or six years of constant use…

This repair seen from the economic side of things may be seen as anti-economical, but at the same time it was not very time consuming and the spare part used was inexpensive, so I can be done. The opposite to what I thought before opening the unit.

When the fault signalled is “no disk”, immediately one would think of a faulty optic group, which is usually the cause of such faults.

Nothing can be taken for granted in this strange world of electronic repairs!!!

Roberto Salerno’s comment: here is another example of a faulty smoothing CAP which may be the cause of many problems, including lack of DVD disc reading.

I can confirm that CAPS are our main job source nowadays.

And thank God that they exist…

Hi there

Riccardo Omage

I’m an Italian  technician  who repairs TV's and other electronic devices. I also write repair cards in Italian,  recently I decided to branch out and translate them into English  for technicians all over the world.
My wife has experience in the technical translation field and she helps me with the translation of these  cards.
My friend Roberto Salerno also co-operates with me by giving  me his repair cards.
These  cards are authentic, taken from our day to day experiences.

> Now we have our first E-book on this subject <
> Our  2nd. E-book on LCD TV's will be completed soon <

If you think that what we have to offer may be of interest or could help you in any way please don’t hesitate to contact me at this E-mail address:

itvrep2@gmail.com

TVC INNO-HIT 21” REPAIR CARD

Roberto Salerno

Brand: Inno-Hit  21”

Model: RF ST TX Silver   chassis 11AK30

Schematic: download from www.electronica-pt.com

Fault: completely dead

Once opened, the first thing I do is measure the voltage presence on the electolytic terminals C809 (150uF-400V), but no voltage results here. The main fuse is not burnt black and gives me a good measurment.
I notice however that the resistor R828 (2,2 ohm-5W) is interrupted.
For sure there is a short circuit somewhere, this reflecting on the fuse and which damaged the limit resistance.
The rectifier bridge, composed of  four separate diodes is Ok, so also for various other components.
I finally find that it is the MosFet Q801 to be in short-circuit between Source and Drain.
On the schematic I see that it should be a 2SK2750, I instead find a P6NK60ZFP assembled.
I decide to fit a 2SK1118 which normally adapts well on these circuits.
Beforehand I try to understand the real cause of the MosFet fault in question.
I check a few things, in particular  the weldings. There is no evident  sign of dry joints however some-thing happens when I stimulate the blue capacitor C811. The rheophore (warm side) found on the welding seems to slightly move. I resolder this welding and others nearby; the new MosFet is already inserted and I replace the R828 resistor (2,2 ohm).

I give power on and the unit remains in standby mode with the red led on. With the remote control I switch on the TV and obtain positive results.
The welding at fault was practically invisible, there were no evident "cold" cracks.
It's important in a case like this to find the real cause of the MosFet shorted.
After a normal test period my repair is complete.

TVC THOMSON 28” REPAIR CARD

Riccardo Omage

Brand: Thomson 28"

Model: 28WX65ES   chassis ICC19

Schematic: download from www.eserviceinfo.com

Fault: stuck in standby

This new client was sent to me by a friend of a friend, he had previously taken the TV to another Technician for repair and was told that it was the "flyback transformer" at fault and it was impossible to find the spare part. I have no faith in a diagnoses done by others (I think it was probably an excuse). As we know even if Thomson is no longer on the market, HR Diemen always have EHT available, the same for other producers of HT transformers. My doubt was that the TV had been ulteriorly damaged. Apart from the fact that it had been inspected by others the original fault seemed to be not one of the easiest.

The TV is blocked on standby, when switched on the red led lights up but with no attempt to switch on.
All voltages exiting the secondary supply section are regular, but the pilot line signal is absent.
As a consequence I doubt that the  microprocessor (or "microcontroller" as Jestine says) is at fault because I have no response from either frontal keys or remote control.
On observation I notice a not original "jumper".
On removal at least the TV makes an attempt to come to life.
The oscilloscope shows me that for a few seconds the pilot line appears on the base of transistor TL001, then also on   pilot transformer pin 1 LL001, but nothing on the base of the final transistor TL030; why is this so?

Explanation:
If cap CL005 is totally open and is not smoothing, nothing passes on the main of the small transformer because the two terminals of the primary spool always have the same potential, there is no signal on the secondary coil.
Needless to say that the replacement of capacitor CL005 cap (470mF-25V) finally resolved the problem, in fact the television restarts to operate normally.

Why the jumper?
My considerations are the following…
Perhaps to put in greater difficulty who would eventually have had to repair the TV? Certain colleagues use the oscilloscope, since going digital it seems to be the most useful instrument for fault finding even if it is more time consuming, others maybe hope for a bit of luck?

In any case, the jumper had been inserted between pins 5 and 6 of the chip IP140 (TDA8139) which operates as a double voltage stabilizer and is found on the secondary supply. Pin 6 is related to the reset function (UP_RES) and goes to the integrated Microcontroller (section R). That is why all functions were blocked. Once the jumper was eliminated the TV was no longer in standby and the pilot line appeared even if only for a few seconds. With the remote control I managed to switch off the front red led, but it then re-activated, at least after this operation I saw that the television gave signs of functioning.
This was followed by a normal repair.

Hi there

I’m an Italian  technician  who repairs TV's and other electronic devices. I also write repair cards in Italian, recently I decided to branch out and translate them into English  for technicians all over the world.
My wife has experience in the technical translation field and she helps me with the translation of these cards.
My friend Roberto Salerno also co-operates with me by giving  me his repair cards.

These cards are authentic, taken from our day to day experiences.

For further information or enquiries, don’t hesitate to contact me at this E-mail address: itvrep2@gmail.com

                                                                           Riccardo Omage