Suyama mj9cnk bad caps?

[KountZERO]

Friend asked me to look at this but all but 1 caps look ok [all are GSC except the one slightly iffy looking fuhjyyu]

The inverters/tubes are working fine however no display appears unless you repeatedly turn it on and off.

I changed the 100uf 400v fuhjyyu mains cap out for another i had kicking around but on reasembly and testing i discovered that without fail, if i remove and reinsert the screen ribbon cable the display comes on perfectly.

In this state the monitor works flawlessly untill the next power cycle.

Do i continue to look in the psu area or is it as i suspect, the logic board that is hosting the fault?

[sabre504]

Re: Suyama mj9cnk bad caps?

Hi as others will tell they may be bad caps even if they look ok .
Have you checked the voltage regulators on the main board ?

[sabre504]

Re: Suyama mj9cnk bad caps?

Just rememberd i have worked on this psu before ,

Red ring check your voltages here as they are connected to the plug that goes to the main board and this will tell you if they are correct .
If they are not correct change all caps and the parts i have ringed in blue check for bad solder joints and cracks or just reflow anyway to play safe .

[KountZERO]

Re: Suyama mj9cnk bad caps?

Thanks for the reply, reflowed the windings as you suggested. The board is giving 12v and 5v at the connector so would i be right in thinking psu is ok?

[sabre504]

Re: Suyama mj9cnk bad caps?

Would seem to be but is that under load ?
Leave it on for 10 mins and check voltages again if they are ok go on to check volt reuglators on the main board

[KountZERO]

Re: Suyama mj9cnk bad caps?

ah i see where your going with it, i have been able to get an image up once the lights have come on, not before. Turning on normaly results in a flashing power LED more often than not or a display that colapses and decays for want of a better description. I guess your saying that its failing under the initial load of sparking up the CFL's?

[sabre504]

Re: Suyama mj9cnk bad caps?

Correct if it fails under load and your CCFLs are ok then it still may be the caps .
The ones i have done had Hermei caps that all looked ok but were out of spec and changing them for a good low esr set cured the problem
Paul

[KountZERO]

Re: Suyama mj9cnk bad caps?

Got a cap set coming from farnells, will report back.

As a side note, was given another 19" LCD today with white screen issue.
Reflowed the solder around the transformers and ccfl connectors and she sprang into life. so thanks for that tip. 1 for 2 isnt bad.

[sabre504]

Re: Suyama mj9cnk bad caps?

Well good glad that one ok ,
hopefully changingh the caps on the other one will cure it

[KountZERO]

Re: Suyama mj9cnk bad caps?

Result! recapping has it firing up 1st go now. Next task is to scrape back some coating on the screen ribbon cable past where the stiffener is. Its frayed and one of the conductors is intermittant right up against where it is creased to lie flat behind screen.

If that doesnt work then i'll canibalise a pata cable for the job lol.

Thanks for the advice.

[sabre504]

Re: Suyama mj9cnk bad caps?

Welcome