Portable fax machine thermal printer printing blocks of black with no text visible

[waigy]

I just got a used possio greta portable fax machine.

It uses thermal printing.

Possio stopped support for these a while ago so I can't get spare parts for it.
The print head is a ROHM KA2008-AF51B 0K300-35371 which I haven't been able to find online.

I've attached an image of what the print looks like when printing any text.
Any idea what causes this?
I've cleaned the printer head, but it was already immaculate.

[stj]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

lets see the board(s) in it

[waigy]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

I can take more (closer) pics if needed.
I don't know if it was good or bad luck, but I just noticed a tiny component after taking the board out the case.
I inspected closely every empty part of the board where this component could fit, but every empty space has two domes of solder in good condition.
The part I found has solder on one end and none on the other so I am confident it has not fell off this board.

[stj]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

yellow tantalum capacitor c600 upper-right looks cracked

can that wifi board unplug? mabe the loose part was under it

[waigy]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

It's not a crack it's a pen mark.

[stj]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

which connector is for the printhead?

[waigy]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

These 4 connecters are connected to the printhead.
I'm aware that the printer only seems to be printing one half of the printhead and at one point faint print appeared on the other half, but it was still just solid blocks of print with no text visible.

[waigy]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

I've looked at every component close up and can't see any burnt or cracked components.

[stj]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

burnd or cracked parts are rare.

check the inductors and caps left of the small connector,
and see where the larger ones go.
is their more parts on the printhead?

[waigy]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

I don't know how to check components though I do have a multimeter.
There are no components on the printer head.

[stj]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

inductors prefixed "L" should have a very low resistance,
capacitors "C" shouldnt.

[waigy]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

Ok thanks what setting should I use on my multimeter?

[waigy]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

I had my multimeter in resistance setup and set to 200 ohms.
The L components all measured the same settling at 0.04 and the C components all gave a brief reading around 80 to 120 then went to zero.
These are the components to the left of the small connecter that is arrowed with my right most arrow ie: C900 to C903 and L900 to L903.
I have no idea if I'm using the multimeter correctly, but I had to press fairly hard on each solder connection to get a reading.
Are there any more components I should check?

[stj]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

those parts checked o.k.
follow the traces from the larger connectors and see where they lead.
i doubt it will help though unless you have a hot-air station atleast.

[waigy]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

I'm struggling to figure out where the traces go.
There are no traces on the rear that come from those connecters.
Would you like close up photos of the board?
I have a soldering iron with a fine tip and I have replaced caps on boards successfully before eg. a 28 inch monitor.
But I have no experience of replacing larger components like chips that have multiple pins though I am a long time subscriber of Northridgefix so I know how things should be fixed.

[stj]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

it is probably a chip if it's not the printhead.

[waigy]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

Is there an easy way of testing the chips on the board?

[stj]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

do you have a scope?

[waigy]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

No just a multimeter

[stj]

Re: Portable fax machine thermal printer printing blocks of black with no text visibl

well,
if you download datasheets for the chips feeding the head you could try checking resistance of the pins to see if any dont match each other.
but i think your in over your head with this.