Need help with a Proscan 32LA30Q - or clone. - Page 1
Forum section: electronics / repair

author: Maddox1
author_rank: Newbie
timestamp: January 21, 2015, 11:14:28 am
content: Good day EEV blog members,I am a long time lurker here, but decided to sign up, as I am in dire need for some technical info on a specific PSU that I have a nightmare getting repaired.The supply in question is a SBGD-200-3HP. This is used in Proscan Tv’s and a lot of clones as wellThe TV model in question is a Proscan 32LA30Q , but was sold here in SA under the Logik brand.The problem was originally a blown mains fuse, after a thorough check I replaced all the electro’s as they were High ESR. I also replaced a 18N50 FET and adjacent 9.1 Volt zenner diode, that had given up the ghost. All other semi’s that I could test, were within spec.The problem now is that with power supplied to the circuit, I do not get any output at all.Scoped the drive to the 2 mosfet driver transistors and there was no drive signal coming from the smps controller IC. And this is where my problem lies. The manufacturer of this board decided to remove the numbering on the IC. I tried online to find any info, but was unsuccessful . The IC in question is a 16 pin DIL chip. On the bottom of the chip is a stamped marking “China 30”, but that is it. On the board it is marked as U3.Does anybody have any info on this chip or maybe a schematic of this supply. I would really appreciate any help/info coming forward.Thanks guys..

author: wraper
author_rank: Unknown
timestamp: January 21, 2015, 11:50:18 am
content: According to the pictures found on the internet, seems to be PWM + PFC controller. Post high resolution pictures of the both sides of the pcb. If you write where is connected each pin, would be very helpful too. Unlikely to get any schematic, rather would need to look for pin compatible controller IC. This IC probably is a Chinese clone of something from more respectable manufacturer.

author: Maddox1
author_rank: Newbie
timestamp: January 21, 2015, 12:27:47 pm
content: Wow!, thanks wraper for the quick response. I will get those pic’s up asap. The only problem is I left my camera with a buddy of mine, and will only be able to get it back this coming weekend. In the meantime I will try and trace the pin outs of this IC as far as possible.Really appreciate your effort in trying to assist me, much appreciated!Regards

author: Maddox1
author_rank: Newbie
timestamp: January 25, 2015, 10:50:24 am
content: Hi Guys,Info as requested:Tracing of ic pins:16- connect to opto coupler via D6 1: connect to pin 2 via 10k resistor15- connect to opto coupler, also connect to pin 13. 2: connect to pin 3 via 10k resistor14- Gate drive for FET transistor 3: see pin 213- connect to Ic U1 4: Connect via transistor to opto coupler12- O Volt 5: connect to pin 7 via 5.1 k resistor11- Gate drive for FET transistor 6: Vcc (positive supply)10- Not connected 7: connects to opto coupler9-connects via 15k resistor to 0 Volt 8: connects via small smd cap to 0 VoltBoth opto couplers PC817 were also replaced. R17-21 are 1.5 Ohm smd devices. I replaced them with normal ¼ watt resistors just to be able to test. SMD parts on order from local supplier.If any addissional info is needed, I will gladly assist where possible. Photos included as requested as well as close up of the IC in questionThanks very much for all your trouble and effort to try and help me solve this issue. Much appreciated.Regards

author: wraper
author_rank: Unknown
timestamp: January 25, 2015, 03:09:52 pm
content: Seems to be pin compatible with SG3525A. Cannot guarantee by 100% as I concluded according to your pin description. Images are low resolution and therefore pretty useless as I cannot distinguish where tracks are going. Anyway if you try it, add current protection between mains and PSU. 100-200W incandescent bulb in series with mains wire will do the job. If anything goes wrong, bulb will light up instead of PSU self destruction.SG3525A is just a PWM controller, without PFC. PFC seems to be made with some another IC in SO-8 package. When PSU output is under load, PFC should produce something around 400V on big electrolytic capacitor (SMPS power cap). Without any load it likely will not work but just pass through rectified mains voltage and there will be something like 300-320V. As Both IC's seems share the same power (if by U1 you mean 8 pin PFC controller), there is possibility that they both are dead. Anyway it is worth to check if there is a power on pins 13/15 (Vcc) in reference to pin 12 (GND), likely something close to 20V or thereabouts.

author: wraper
author_rank: Unknown
timestamp: January 25, 2015, 03:15:19 pm
content: BTW it seems that there is Standby PSU in addition to the main one on this board. Does it work? As I see multiple optocouplers on the board, main psu likely needs to be enabled with signal through optocoupler to start working.

author: wraper
author_rank: Unknown
timestamp: January 25, 2015, 03:18:33 pm
content: Standby PSU should be driven by PWM controller in the small 6 pin package.

author: wraper
author_rank: Unknown
timestamp: January 25, 2015, 04:17:54 pm
content: A bit more research. UC3846 seems to be closer than SG3525A. Also it is what you more likely would expect in the such PSU. It have very similar pinout but pin 16 is shutdown, which you would expect to be connected to optocoupler in such configuration. Anyway, if standby PSU does not work, main PSU won't work too even if it is completely OK. Therefore check that first and probably you do not need to replace this IC at all.

author: wraper
author_rank: Unknown
timestamp: January 25, 2015, 04:35:23 pm
content: likely it is MC0628R. 100% the same look. Seem to have the same pinout as UC3846, however some source state that there is some incompatibility between them. Therefore if you try to change it, buyMC0628R.

author: kripton2035
author_rank: Super Contributor
timestamp: January 25, 2015, 04:40:09 pm
content: you said you changed all the capacitors, but did you change the small (10µF or so) that must be between the pin 15 and 12 of this UC3846 or equivalent ? because often this one gets dry, more often when it's beside a big heatsink like it seems to be there.

author: wraper
author_rank: Unknown
timestamp: January 25, 2015, 04:53:52 pm
content: Here is the schematic of this PSU. Somebody on polish forum posted it, could contain errors as someone draw it from actual PSU.

author: Maddox1
author_rank: Newbie
timestamp: January 25, 2015, 06:10:22 pm
content: Guys,You’re the BEST!!!!THANK YOU, THANK YOU, THANK YOU!Wraper, yes the Psu does have standby, I will check out all according to your directions.Kripton2035- Yes I replaced all electro’s , as most of them were way off value and had high ESR.I did try to upload with the original pictures (size +- 4 Meg each), but were unsuccessful. I then used a re size program to get it to a “smaller” size. I must have screwed up somewhere with that. Apologies for thatI will use a current limiter (ballast lamp) before I power it up.Now I just have to order the IC needed from RS components. I will supply feedback as soon as I have any news.Once again I really appreciate you guys taking the time and effort to help me out.Thanks So Much!!!RegardsMaddox

author: wraper
author_rank: Unknown
timestamp: January 25, 2015, 07:46:44 pm
content: You won't get MC0628R at common places, only somewhere from China. Some strange beast, no datasheet available. Therefore look on ebay or aliexpress. On one Russian forum people white that UC3846 do not work as replacement in slight modification of your psu, like on picture I posted (with different heatsinks, there are holes for such on your PCB too). Actually I found this schematic and PSU photo by searching for MC0628R, not PSU model as it is different but obviously PSU is almost the same. BTW if going to order from China, do it soon, otherwise your order will be delayed by few weeks because of the Chinese new year.

author: kripton2035
author_rank: Super Contributor
timestamp: January 25, 2015, 08:24:28 pm
content: clearly the MC0628R is not the same as the UC3846according to the datasheet of the UC3846 and the schematic you gave uspin 15 of the uc3846 should be the power supply, and is not connected on your schematic but it should be on pin 16 ?these two circuits are non compatible.

author: wraper
author_rank: Unknown
timestamp: January 25, 2015, 10:33:11 pm
content: Quote from: kripton2035 on January 25, 2015, 08:24:28 pmWhat I see, there are dots on the pins 13 and 15 (power). As I said this schematic could contain errors/ be incomplete as someone just had drawn it from existing PSU. Maybe you didn't notice but there are no other pins for powering the IC. There is optocoupler with one pin not connected too.

author: Maddox1
author_rank: Newbie
timestamp: January 26, 2015, 10:26:35 am
content: Guys,You are spot on. I tried all the local suppliers , even one that specializes in Chinese parts. No one was able to help me out. I now have placed an order with a seller on Allie. Will take a while to arrive, but luckily i'm not in a big hurry to get this supply fixed, so don't mind the waiting time.I will update with progress once I have received the IC's.Once again thanks so much for all your trouble and effort, I really do appreciate it.RegardsMaddox