Trying to repair a dreambox 500HD. Can´t find what kind of IC it is. - Page 1
Forum section: electronics / repair

author: Tony.T
author_rank: Regular Contributor
timestamp: May 07, 2015, 12:31:56 pm
content: Found the problem. Shortcut in this fellow. Got warm as hell and making strange sound.But can not find what it is on the web. Somebody??? Please.... what kind of IC is this?Thanks in advance....

author: bktemp
author_rank: Super Contributor
timestamp: May 07, 2015, 12:44:12 pm
content: http://www.vishay.com/docs/69004/si4128dy.pdf

author: Tony.T
author_rank: Regular Contributor
timestamp: May 07, 2015, 01:08:26 pm
content: Thanx a lot.How did you find it? Experience?Are you really sure that it is a Si4128DY mosfet? As i could not find the same model number.Not that i do not trust you ...just curious ...want to know if you have a special homepage or something like that.Anyway....THANKS A LOT...

author: wraper
author_rank: Unknown
timestamp: May 07, 2015, 01:47:37 pm
content: Yes this is Si4128DY mosfet.

author: jlmoon
author_rank: Unknown
timestamp: May 07, 2015, 02:49:59 pm
content: Tony,To answer your question; There are a few on here that are true Blood hounds when it comes to identification of parts, their pedigree and sometimes how to locate replacements. It all comes down to experience in the field.

author: bktemp
author_rank: Super Contributor
timestamp: May 07, 2015, 03:02:40 pm
content: Identifying SMD markings can be really difficult, but this was very easy:The second line starts with the Siliconix Logo.If you can identify the manufacturer the most difficult step is done.Then I simply put Si and the number into google and got the datasheet.

author: Tony.T
author_rank: Regular Contributor
timestamp: May 07, 2015, 03:15:46 pm
content: bktemp.Thanx mate.....true Sherlock holmes candidate :-)jlmoon....well...don't ever underestimate experience right

author: macboy
author_rank: Super Contributor
timestamp: May 07, 2015, 03:38:24 pm
content: I would love to have a "cheatsheet" of various semiconductor manufacturer's logos. I am good at identifying maybe the 10 or so most common, but would not have known this one.

author: bitwelder
author_rank: Super Contributor
timestamp: May 07, 2015, 05:06:48 pm
content: Quote from: macboy on May 07, 2015, 03:38:24 pmSomething like this one?http://www.elnec.com/support/ic-logos/?method=logo

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 07, 2015, 05:08:20 pm
content: Or this:http://320volt.com/wp-content/uploads/2011/03/yari-iletken-uretici-logolari.pdf

author: Tony.T
author_rank: Regular Contributor
timestamp: May 19, 2015, 06:50:02 pm
content: Could somebody please help me on this sucker?I have replaced the first mosfet chip with this one...Si4128DYBut still there is a strange noise and the mosfet goes HOT. When i desoldered it...no more noise.i have measured 6v into the Gate of the Si4128DY. This is way to high...the spec sais max 2V.So i followed the trace and found this attached chip. Pin 2 from bottom left hand side.... but can not find what kind of iC it is.is it a similar chip to this one ??http://www.ti.com/product/lm2742http://www.ti.com.cn/cn/lit/ds/symlink/lm2742.pdf??It still sais -0.5 to +21V??But something is making the mosfet to make strange noise...and i still think that 6V into gate is to high...or am i missing something?

author: Jane
author_rank: Frequent Contributor
timestamp: May 19, 2015, 07:37:21 pm
content: Have you tried to use a new power supply adaptor?

author: Tony.T
author_rank: Regular Contributor
timestamp: May 19, 2015, 07:44:23 pm
content: Yes...i have. I use a bench power supply to test (rigol 832A). As soon as the mosfet is in place....the sound appears...the powersupply stops at 7V even if it should be 12V..but that is because i have a current limit at 1A.Sooo...there is a shortcut somewhere... when out of the circuitboard....there is no sound and no extremely heating anywhere...I bought a new mosfet and the same with the new one. The drain and source seems ok...but the gate receives 6V....from the second chip that i posted last...

author: Tony.T
author_rank: Regular Contributor
timestamp: May 25, 2015, 01:16:07 pm
content: Damn..... okej...a newbie mistake but i´ve solved it at last :-) .. Just wanted to say how...and make others not to do the same misstake.Used a external powersupply with limit 1 A. It stopped at 7V and showed 1A current consumption. My guess was that something was shorted as the powerfet got warm as hell. And some strange buzzing sound.My mistake was that i should have put the limit to 3A...just because the original powersupply of the dm500HD was 12V 3A.My Rigol stopped increasing the voltage as the limit of 1A was reached. But that is only for a second...then it decreases.The problem was simple...not enough current to the 500HD...EVEN if i measured 12V without a load.Soo...by increasing the current limit to 3A...everything started to work.....so..no error on 500HD at all. Only the original powersupply. That i have openen and i saw the problem directly....a cap with the top like parachute :-)BUT...anyway....i question is rises directly....and something that i want to understand...and talk about.When i did not have enough voltage....the powerfet above (the first picture)....got warm as hell..... The question is WHY? Why did it got warm and buzzed like it was a shortage?Is it because the whole unit did not got enough power and the switching power circuit inside did not worked properly...and therefor had a much lower switching frequency and therefore larger time when more or less shorted to ground and therefore consumed more power and getting to warm?Or what is the reason of getting that warm? because...now with proper powersupply at 12 V...it works fine.Somebody please? Want to understand the behaviour...Cheers...

author: PA0PBZ
author_rank: Super Contributor
timestamp: May 25, 2015, 01:59:11 pm
content: Short version:When you need a certain power out of a regulator you need to supply it with the power + losses at the input.So when you put in 7V instead of 12V it draws about the double current and could get rather hot...

author: Tony.T
author_rank: Regular Contributor
timestamp: May 25, 2015, 04:14:50 pm
content: Aa....stupid.....simply ohms law....Well...there you see...sometimes one just think to much :-)Thanx mate...

author: ro0ter
author_rank: Contributor
timestamp: October 10, 2016, 07:52:08 pm
content: Hello everyone,I am also t trying to fix such a beast... Problem is that a bad dish motor burned a bso300n03s (like blown gate, that bad), next to the lnbh21pd and I replaced the n-mosfet with a bso110n03ms (double the current).The thing is that the entire PSU rail (input 12v/3a) is now at about 2.89v and constantly dropping to 2.5v, more than 3a being consumed...I then noticed that the new MOSFET was heating like hell and I then desoldered it... Dreambox seems to start, a couple red LEDs remain lit, the yellow/green front led blinks then in another try the front red LED blinks, but the problem is that the input stays constantly at 1.5a and the lnb21hpd hearts very much (not as much as the MOSFET, yet very much)...How can I fix it? Anyone has any ideas? Should I change the LNB21? What else should I check?Thank you in advance!

author: Jane
author_rank: Frequent Contributor
timestamp: October 10, 2016, 08:13:53 pm
content: Check the output voltage on LNBH21. It should be 13/18V.

author: ro0ter
author_rank: Contributor
timestamp: October 11, 2016, 05:28:57 am
content: Hi Jane,Should I check the output voltage of the LNBH21 while there is no soldered MOSFET next to it? I get ruffly 11.8v (I guess this is the supply voltage rail). If I add the MOSFET, it gets down to 3v and the MOSFET boils instantly. Without the MOSFET the LNBH21 gets to its boiling point, but much slower. I tried to sniff the I2C bus but I get lots of start conditions and notging else (no other data)... I do not own professional tools, but this cheap logic analyzer never disappointed me.My best guess so far is that the LNBH21 is toasted as well...

author: Jane
author_rank: Frequent Contributor
timestamp: October 13, 2016, 08:00:30 pm
content: I would check a resistor to SENSE pin of LNBP21

author: ro0ter
author_rank: Contributor
timestamp: October 14, 2016, 05:53:44 am
content: Will do that later on today or over the weekend. However I am not very optimistic about this repair since the I2C bus is not working correctly and after I hooked the beast on the cp2102 serial to USB (service labeled USB plug on its back) I got some interesting data.. sometimes it would boot all the way, status LEDs 2 and 5 on (numbering starts near the front LEDs/button ribbon plug), front panel red LED blinking, yet with lots of errors (overcurrent situation on hub 1-0:1.0 + hub 2-0:1.0 plus lots of retrying i2c transfer for the bcm4505) and sometimes it would simply call it's flash corrupted and not boot at all (no status LEDs lit, front panel green LED blinking)... Should I upload some files here? Please note that i was only able to make the beast speak if the MOSFET controlled by LNBH21 is not soldered on to the board. I know that this is no dreamBox forum but should I upload any diagnostics files? Would they be of interest for anyone?Thanks again!

author: bobaruni
author_rank: Regular Contributor
timestamp: October 14, 2016, 11:53:53 am
content: I don't know if this will help but I had a DM500HD where the LNB voltage was cutting in and out and after a few weeks it had no LNB voltage and the fan was squealing and running very slowly.Apart from this, the software seemed fine except it wouldn't pick up any bouquets.I also thought something was short.When I measured the 12V rail, it was only 7 or 8 Volts.I opened the power brick and found that the 1000uF 16V cap was dry.Replaced the cap and all works fine now but I spent a lot of time around the LNB circuit trying to understand why the 12v/18v was not present when really it was the power brick.The power brick's voltage measured fine until you loaded it with more than 1A.