Problem with HP-19C Printer



#12

Hi all,

I have a HP-19C that is working practically 100%

Even the printer generally works well, BUT, the first line of every character never appears,
for instance:
The 5 should appear like this:

****
*
***
*
*
***
but in fact appears like this:
*
***
*
*
***
Can anybody give some help about what to fix here? I already opened it and put some lubricant but it remains the same.

#13

Hi,

first thought is that there's still some dust remaining.

Second thought: Maybe a loose contact in the flex cable.

Third thought: burned print needle...

HTH

Raymond


#14

Fourth thought: a failed transistor in the print head driver chip.

Edited: 9 Aug 2006, 6:09 p.m.


#15

My 2 cents:

I think it's strange that the printhead only the first row is failing and not anymore the followinglines, as if he has to warm up first.

Could it a capacitor problem having problems aquiring his charge ?

Are all the other dot's deep black (or blue) ?

Ronald


#16

No, the printhead has 7 (IIRC) elements in a vertical line and puts down entire characters as it moves across the paper.

If you're missing the top row, then I would suspect :

The flexiprint cable that links the head itself to the lower (PSU/printer) PCB. Alas repairing that is next-to-impossible.

The head itself

A driver transistor (I think there are a pair of quad transistor array 'chips') on the PCB, like in a Topcat.

The PIK (Printer Interface and Keyboard) chip on the logic PCB.

You can get schematics on the HPCC CD-ROM.

I measure the resistance between the common connection on the printhead flexiprint and each of the others in turn. If one is much higher than the others (or is open-circuit), then you have a head/flexiprint problem.


#17

Can you explain better were I measure the resistance ... I can't find any suitable place.

#18

It it almost certainly a resistor in the printhead. You can check this by comparing the resistance of each dot with an ohm meter. Two of the connections on the flex cable are ground, the other are the dots. Resistance from ground to dot should be 10-15 ohms (and pretty consistent for each dot). I think you will find one dot open.


#19

I'm trying to test the resistance but I can't, how do you do that?

In one side I have the integrated circuit from here the connection to the print head leaves, but on the other side (the print head) the only place were I can check the resistance is in the print head itself ... and the contacts are so tiny I can't check anything.

Am I doing this wrong?


#20

As Tony Duell calls it, the flexiprint cable needs to be released.

Best wait till someone more familiar with it, but on 43A/62A I use a cut down credit card (extra thin plastic) to slide alongside the cable to release it. Be carefull, it's irreplaceable, don't use a lot of force. HP spec special release tool but never give picture of tool.

Just guessing here, never seen inside a 19C myself. I wonder if the printhead is anything like the 82143A printhead?

Best

Edited: 11 Aug 2006, 11:10 a.m.

#21

The contacts to the cable can be accessed at the connector. There is no real need to unplug the flex cable. You may need to wrap a piece of wire around the probe to touch the contacts, but part of the gold contact area of the flex cable end almost always sticks out a bit from the connector.


#22

Well, I really can't get to the contacts in the side of the printing head, but, unfortunately, I think I saw the problem.

In the connecting PCB there is a break that crosses one of the connectors :-(

Anybody knows how to fix it? To me it seems almost impossible.

Anyway, I'll not be able to answer your suggestions the next days since I'm going outside town, so ... thanks in advance for good tips.


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