A600 recapped but now with colour issues

[swood123]

Hi all,

I have an old A600.  It did run before but I was worried about capacitors leaking.  I had already recapped my A1200 so was quite comfortable with recapping an A600.  When I stripped it down some of the capacitors had started to leak and it was smelling really bad so I had to clean it prior to recapping.  On recapping and restarting I am now getting a black background on my startup screen and it looks like also in software/games.  I have rechecked continuity of all the smaller tricky caps and refloated any that maybe a problem (you amy notice in the photo I have rotated one smaller cap slightly as I had a damaged pad),  I cannot see what I am missing.  Could a larger capacitor be my problem?   

FYI> I did remove the TV modulator to gain access to the smaller caps by the power supply.


Regards

Steven

[swood123]

Okay I shall swap out the transistors.  Just need to find somewhere to get the replacements.  Out of interest can you advise how I measure the R, G and B signals?  I dont have an oscilloscope, only a multimeter.

I did clean the board.  I gave it a wash with electronic cleaner.  Then used ISO on the areas that were affected by corrosion.  I did think about leaving the RF module out but wasnt sure if it affected anything.

Thanks

Steve

[swood123]

Excuse my ignorance but can you confirm which one is the Sony chip?

[swood123]

I have found the schematics now. 

Thanks making more sense.

Looks like I shall remove the U12 chip as suggested and I shall remove the transistors (one looks in bad condition).


Regards

Steven

[swood123]

Thanks for advice/direction.

I just ran a diode test (with no power to the board), across the three suspect diodes (Q231, Q232, Q233), and they all seem bad.  They work from Base (+) to collector but when I checked collector (+) and emitter (-) and they are all allowing voltage (I get a reading on multimeter).  However on other transistors I just get a 1 which on my multimeter is no contact.

On checking all subsequent transistors I have also noticed Q511 is looking suspect too; this is an 2N3904 transistor also, for power up reset.

Luckily I have some replacement transistors on order.

So now I believe I need to remove Sony chip, check and clean underneath and then swap out all suspect transistors. 

Hope I have captured all.

Thanks for guidance all.


Regards

Steven




 

[swood123]

Hi all,

I checked the voltages from transistor to ground, I believe I see the below values.  I am not seeing 2.2volts as mentioned previously anywhere They are all giving the same value.  I also removed the Sony chip, cleaned below it and resoldered it back into place.  Now my screen has gone very dark (I can barely see colours on screen). Now wondering if my Sony chip is actually bad as I seem to have made the picture worse removing and reinstalling the chip.  The other thing I was wondering is if I should also remove the IDE connector as a number of pins on this had gone green.  There maybe capacitor leakage below it.  Any direction appreciated.  I have bought a replacement Sony chip as I shall replace this now anyway.

V pin 1(B) to GND   V pin 1(B) to pin2 E          V pin 1(B) - 2E
Q231   0                     0                                   -5.04
Q232   0                     0                                   -5.04
Q233   0                     0                                   -5.03


Regards

Steve
         

[swood123]

I believe you are correct.  I did have a damaged pad but I assumed the pin didnt go anywhere I did check schematic and assumed it was pin 5. I assumed first pin was right next to the indent at bottom left.  On closer inspection and after removing the chip I can see it may actually go to a round contact right below it.  See attached pic.  What are your thoughts on this?


Thanks for your help with this, it's been an interesting learning curve for myself.

Amendment.. I just read Screwtops link, thanks.  The link to the schematics is quite handy but from it it does look like pin5 for the Sony chip doesnt go anywhere... :/

It looks like I may have to do some continuity testing accross the board using the schematics website..



Regards

Steven

[swood123]

I had the negative lead on the shielding for the TV outlet and I put the positive on the Transistor (bottom left connector), which I understand is base.  I have been using a brand new modern power supply I bought, surely power supply should be okay.

I guess to recheck I assume I will need to resolder the Sony chip back to the board now.  I shall do this later when I get away from work.


Regards

Steven

[swood123]

I replaced the Sony chip and checked continuity to all contacts around the chip, they were all fine and then I decided to just check over the whole board and I noticed a small short on the back of the board....... it now works

Well what a learning curve that has been for me.  Very enjoyable.  Now my son can play some games on it

Thanks all for the guidance.


Merry xmas

Steven