Intro plus help for Medion MD33332 Now fixed

[OldLes]

 Hi everybody.
I am new here, just registered. I live on the Isle of Man; amongst other things, I used to be a TV repair man, and compact disc players (20 years ago, now retired). We have "amenity sites" here, and there are many LCD tvs discarded, some with no faults (but need freeview box), some with serious faults, but many worth looking at.
Presently I have a Medion MD33332, which we used as a bedroom set, but which developed flashes on screen. Have isolated (with freezer) an IC, 1084 which is responsible. Where can I get one? Is there a circuit available? This IC is on the tuner / video / sound board. If it helps to identify, it uses a MEGMEET PSU, the same as I see here:--
http://www.shopjimmy.com/megmeet-mlt666-rev-2-8-power-supply-unit.htm
A circuit for the MD33332 would be helpful.
I have two more sets I need circuits for, but will post them later.
OldLes.

[OldLes]

I notice I have had 47 views but no responses. I have just been reading through a few posts on another page (don't know my way around here yet) and I wonder if it is because I have not given enough info, so here is everything I can give.
TV is a Medion MD33332 (I presume is is something else badged as Medion?).
It has a MEGMEET PSU with number MLT666,   Rev:28.   2006.126
The Main board (tuner, sound etc) is HDM9L-V 6.3. Serial No. 800302H0563F
This board carries a paper label:--  02     07/09/21
                                                T02H05/E001
                                                KEY 020585
The display is a Samsung LTA320WT-L16     7Y7D17B35H
The inverter (which has 4 duplex transformers) is SS1320WA16   Rev.06
It would be useful to view a circuit, and I wish to replace the 1084 IC which I have identified by freezing as faulty so need a source. My pal found one on a board, but though it said 1084, it was rather smaller. Same size as a TIP41 for older engineers. 25 years ago I used to spend many hours advising on Grundig faults and supplying panels at a price you could afford. Now I need advice.
OldLes.

[Keith]

Hi,

This type of power supply suffers from faulty capacitors, I would check the electrolytic's for high ESR. This causes high ripple / noise on the supply lines and could be causing the semiconductor to overheat.

Unfortunately, identifying some semiconductors in modern equipment can be very difficult, even if you can identify it, it can be near impossible to obtain a replacement! And schematic diagrams are as rare as rocking horse poop.

Good luck

Keith

[jordan]

Medion chassis type MST9E88L  MST9/MSTAR

[Keith]

Hi OldLes

I have 5V and 1.8V versions in TO220 (TIP41) case on a board, can remove if you want.

Keith

AIC1084
5A Low Dropout Positive Regulator
FEATURES
Dropout Voltage 1.3V at 5A Output Current. Fast Transient Response. Extremely Tight Line and Load Regulation. Current Limiting and Thermal Protection. Adjustable Output Voltage or Fixed 1.5V, 1.8V, 2.5V, 3.3V. Standard 3-Pin Power Packages.

DESCRIPTION
The AIC1084 is a low dropout three terminal regulator with 5A output current capability. The output voltage is adjustable with the use of a resistor divider or fixed 1.5V, 1.8V, 2.5V and 3.3V. Dropout voltage is guaranteed to be at maximum of 1.4V with the maximum output current. Its low dropout voltage and fast transient response make it ideal for low voltage microprocessor applications. Current limit and thermal protection provide protection against any overload condition that would create excessive junction temperatures.

APPLICATIONS
Mother Board I/O Power Supplies. Microprocessor Power Supplies. High Current Regulator. Post Regulator for Switching Supply.

TYPICAL APPLICATION CIRCUIT
VIN 5V 3 AIC1084 1 ADJ C1 + 10µF 2 VREF VOUT 3.3V

RF1 125 + 1% C2 RF2 10µF 205 1%

VREF=VOUT -VADJ=1.25V (typ.) VOUT=VREF x (1+RF2/RF1)+ IADJ x RF2 IADJ=55µA (typ.) (1) C1 needed if device is far away from filter capacitors. (2) C2 required for stability.

Adjustable Voltage Regulator

VIN 5V

3

AIC1084-33 1

2

VOUT 3.3V

C1 + 10µF GND

+ C2 10µF

Fixed Voltage Regulator

Analog Integrations Corporation

Si-Soft Research Center 3A1, No.1, Li-Hsin Rd. I , Science Park , Hsinchu 300, Taiwan , R.O.C. TEL: 886-3-5772500 FAX: 886-3-5772510 www.analog.com.tw

DS-1084P-03

010405

1



[OldLes]

Kieth, many thanks for your replies. I found a link to the 1084 on RS website:-
 (  http://uk.rs-online.com/web/c/?searchTerm=lm1084&sra=oss  ) but the choice of device variants left me confused. What I will do, maybe tonight, time permitting, is to power the set up again, check the voltages on both the suspect and adjacent good 1084, and try to decide which version I need.
Maybe one of yours would fit the bill, let me measure first.
I will try to get a scope on it and look at the ripple in view of your earlier comment; what is the maximum I should tolerate would you say?
Jordan, your references confused me. Google just leads me to an IC, not a chassis, or am I missing something?

[Keith]

I have a similar chassis in at the moment!
The type can be identified by the number after 1084, i.e 1084-33 = 3.3v, 1084-50 = 5v e.t.c. No number after 1084 will probably be a variable type. Also if pin 1 is connected to ground it will be a fixed voltage type.

Keith

[sleepy]

"Jordan, your references confused me. Google just leads me to an IC, not a chassis, or am I missing something?"

At the end of Jordan's post you will see what looks like a paper clip, click on it and you'll get the service manual for this set in pdf format which opens with Adobe reader.
Hope thats clearer m8.

[jordan]

MST9E88

[jordan]

MST9E88 ver.2

[OldLes]

Thanks guys, now the info is coming in.
Earlier, I said "  Jordan, your references confused me. Google just leads me to an IC, not a chassis, or am I missing something?  ". Simple answer, I was missing something. Most of the time I have read the replies "anon"; I now see the pdf is only visible whilst logged on. Lesson learned. Thanks Jordan, I will study all three manuals with interest.
Kieth, it looks as if you are correct, it must be an adjustable one. The (output volts) - (ref pin volts) = 1.242V and 1.237V on my two 1084 ICs. Since this is not equal to 1.8, 2.5 or 3.3V (data from a sheet I googled) nor 1.5v (Kieth's data) then that makes " adjustable" the logical choice. My datasheet also indicates it is a "D" package, whilst the one my pal found was a D2 package.
I scoped the pins for ripple, measuring 0.85V p-p on one IC, and 0.6V p-p on the other, with no obvious change as the fault developed as the suspect IC warmed up. This was at a frequency of about 1.1MHz (0.92 micro secs cycle time)
I think I now have enough info to order the correct 1084 version.
Thanks again, and I will report back after I get one and fit it.
OldLes.

[OldLes]

I ordered a replacement 1084 chip, had to buy five, so total bill £19.
I replaced the IC, and ran soak test with no problems.
Should anybody else have one of these, when you remove the signals etc board, all the plugs fall more or less in the correct place. However, there is a multi lead near to the fauly 1084 (U5) which feeds off (to display I assume) from a 36 (ish) pin connection, but the plug has six less places in the plug. There is an arrow on the PCB suggesting Pin1, but in fact the plug is offset so the other end is fully populated!
I could not fully relate the circuits to any of the three which Jordan linked to, so I guess they change things around every couple of months or so during production.
Thanks again for all help, OldLes.