Trouble identifying pin 1 on 3832B in hp smps

[wedgetail]

I followed the very big thread on Rigol oscilloscope investigation about a year ago. This is my first post as I am struggling to identify pin outs on the 3842B SMC footprint. My background is a lifetime in industrial instrumentation amongst this a lot of computing and associated electronics.
 
I am now retired but I like a simple electronic challenge now and then. A family member passed me a dead HP printer switchmode power supply, 32V, GNF, 16V output voltages. No output to be measured. I have found a number of internet hits regarding such power adaptors and have a fair idea of how to go about troubleshooting this, especially if I can find a schematic. Even before I need the schematic I have pin identification problem on the smc 3842B item.

hp Invent Ac Power Adapter  0,+16V,+32V   using following information I have googled a lot but not managed a schematic yet.

0957-2094
5905684046 Rev A1
PA-2400-02H --->> LiteON

I am attaching a section form the circuit board showing the IC in question.  I thought I had got a good start by following the startup circuit of about 1 Mohm and a capacitor connected to pin 7 and then checking pin 5 being GND because I know where the high cap ground is and assume that pin 5 would be gnd but when doing a ohms test I find about 20kohm to pin5.

If I rotate the "pin1" start point 180 degrees I do get 0 ohm to the new pin 5, but now I have not yet identified the pin 7 expected startup circuit.  Due to this confusion I decided to look for help.

Any suggestions to pin out on the picture.

[Armadillo]

The bar always on the left, and pin 1 on lower left [see pic]

[Jay_Diddy_B]

Hi,
There are only two possibilities. I favour this one:




For the following reasons:

1) there is a star on the PCB adjacent to this pin.
2) there is a slope on the package.

Good luck !

Regards,

Jay_Diddy_B

[wedgetail]

Armadillo / Jay_Diddy_B
Thank you both for replying.

I came to same conclusion initially by following the two 6493 smc series connected resistors in the second picture I attached. These ar connected to the 350Vdc I can measure on the big cap when carefully powered up. Added to this it seems there is a smc capacitor associated  when going to pin 7.

With no power conneceted I expected to get zero ohms measured from pin 5 to GND but not. 

The slop on the chip leg side was very well spotted, I decided after using my USB micro scope to take the pictures that there probably was a slope,  but the Unitrode data sheet I used did not indicate such.  The bar on the case I assume was a form of logo but I did not recognise this either.

Armed with confirmation of pin locations I have just revisit pin 5 testing and indeed get "zero" ohms.  Well at least I will attempt to measure the voltage on pin 7 with my multimeter when 250V AC power applied. Considering my age and gong ho attitude plus being well past midnight I am not going to do this tonight. 

Stay tuned

[Andy Watson]

2) there is a slope on the package.

Agreed. The datasheet shows a significant chamfer on the edge that denotes pin 1. It also shows the bar in the code markings as indicating pin 1.

but the Unitrode data sheet I used did not indicate such.

Try this one:
http://www.onsemi.com/pub/Collateral/UC3842B-D.PDF

[wedgetail]

Andy Watson
Thank you for replying.  You are correct, I downloaded the ON-Semi data sheet and it is quite clear.

General
Just before shutting down for the night, I measured the two 6493 resistors, I made the assumption this meant 649 kohm but I measure several Mohm for both.  Perhaps I have found something here?  Well it is my  time now.

[GuidoMonstrey]

Hi mr Wedgetail,
i do have the same problem with a power-adaptor HP 09572094 (for a PSC 1417).
Sometimes the power-adaptor works and sometimes total nothing (no 32v and 16v)
I looked at the elco's  if they were still oke with an ESR-meter. And i did find some less good elco's. I have replaced them but until now nothing......
Did you find out more since your last post please?
Are the resistors (2 x 5493) still good?
Or did you find other things?

Please , if you are not busy, let me know?
It is so sad to put this adaptor in a kind of trash....lol.....
thanks

[wedgetail]

GuidoMonstrey

Welcome, I notice you have only just joined forum, like myself. Thank you for posting as I was reminded that I still have this problem to be solved. Like you I do not like to throw away items that could be recovered.  The powersupply has special interest as I have meant to practice my understanding of switchmode units.  My theory is sufficent but I lack practical experience, especially on very hard to get at items. On this powersupply I had to try and remove a lot of white probably form of silicone to see a few components under it.

No I am no further, the opened unit sits nicely fixed to a base board so it is firmly supported and I can place test probe firmly on the board without it slipping away from me.  I no longer recall what problem took over my time, there so many other things I try to work on.

Right now I am working on a hp Pavillion laptop dv6-3132tx, my neighbour had taken it to local repair shops, they  told him it was uneconomical to even try figuring out what was the problem.  When plugged into the mains absolutely no life, with the battery removed. I understand he paid aroun $A1500-2000. He has hardly used it.  I promised I would have a look and see if at least I could save content from his hard drive. This is no problem, it reads from insertion into an external USB box.

I then suggested he would not loose much if I stuffed up taking it apart and look further but I would need several months at least until I found time.  So happened that last week I could start looking and that is what I am doing right now.  Came back to this forum to see if anyone worked on laptops here.

Anyway I am digressing, back to your post.  Ok so I am no further but let us get some more details from you.

1.. Do you work from a schematic diagram of the unit?  Or a generic schematic just showing principle?
2.. Have you identified the integrated circuit on you unit? 
3.. Will you be able to post photos if necessary.

You mention you have measured ESR values on the electrolytic, does this mean your are an electronically minded technician one way or another. I ask because I assume this means you have some background in electronics but I could be wrong.

Regarding my resistors, I think my last memory is that I was uncertain I had the correct ones located but at least they wer not open circuit, there was voltage on either side.