Tom Jobe

asked Aug 15, 2009 at 5:21pm
Hp HP DeskJet Plus

HP 4L and 4P controller board repairs

Hello Everyone,
This week I posted about a blank page problem on an HP 4P (The 4P later died completely!) and Moe got me pointed in the right direction (Thanks Moe!).
I also have two dead HP 4L printers, one of which I have had apart for some time. From time to time I study the controller board, and work on developing a partial schematic for it. Today I spent some more time on the 4L controller, and found the +12 volt and +5 volt supplies to be working. I have not been able to find any evidence of the -5 volt supply mentioned in the block diagram in the 4L manual, but that is where I quit working on it today.
I don't suppose a schematic has surfaced for the 4L or 4P contoller over the years has it? A look around the Internet does not turn up any information about any such schematic.
I fully realize that it does not make a bit of sense to try to fix a 4L or a 4P, but I find it interesting, plus I learn a little something about analog electronics at the same time.
If anyone knows anything about the 4L or 4P controller board at the component level, or knows where a schematic can be obtained from, please let me know.
Thanks!
tom jobe...
I took a working 4L to a recycling event last week just to make room in my basement, I also took 25 other HP printers. I have about 4 more 4L printers, in my collection, you might be able to talk me into parting out one. ;)
by Stephen on Aug 16, 2009 at 11:19am Add comment
Hello Stephen,
Let's talk!
My goal in all of this is to possibly learn how to fix one of these un-fixable controller boards. I bought another working 4L for $10, but it quit the second time I turned it on so I lost my working comparison board.
I'm near Los Angeles when you go to figure the shipping.
If it is the slightest problem for you, I can probably get another 4L at the monthly local swap meet that comes up in two weeks.
tom jobe... - Tom Jobe
A search of the forum archives this morning turned up this good clue (pasted in below).
I will have a good look at the 4L controller board solder connections today.
tom jobe..

>>>Just on a hunch when someone said to try plugging the ac cord a few times to see if the leds do light up, well it did for me once and I actually go the printer going again to print 30 pages, then after a long time out the printer never came on again. The sleep timer seems to cut power off permanently.

After a few days of trying to give the printer away as parts, I took another shot at checking the motherboard out near the power ac assembly. I flipped the circuit board over and look around, I didn't like the soldering connections I saw so I just resoldered starting from the ac plug to the circuit board and followed whatever it connected to about 7 layers deep. Slapped all back together and plugged the ac cord in and the leds lit up!

Reconnected back to my print server box and printed fine again. Waited for it to time out and it woke up from a print request. Then I printed a 40 page doc and that looked OK. Let it go to sleep and then printed a test page again and it woke up and printed fine!

How long this will last,dunno!<<<
(from retiredman)

by Tom Jobe on Aug 16, 2009 at 8:27am Add comment
Stephen is over in W. Virginia. I guess you must be talking about the TRW swap meet since the ACP is in Sept. Don't remember seeing any 4Ls or 4Ps at the TRW recently. I stripped all the 4Ls I have of their controller boards. I might have a working 4P. Just sold a refurbed one to someone. People love their 4Ps.
by moe on Aug 16, 2009 at 7:54pm Add comment