A600 recapped but now with colour issues

[F0LLETT]

Had this the other day.

Remove sony chip and check underneath, one I worked was recapped by someone and they didnt clean leakage under chip. Had to also clean up Q231, Q232 and Q233. This caused exactly same colour issue.

[F0LLETT]

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

U12

[F0LLETT]

You'd need an oscilloscope to measure the RGB signals.  Your multimeter will have a diode test function which you can also use to quickly test the transistors.  All bipolar transistors will measure as though they're two diodes.  For the 2N3904, which is a NPN transistor, leave the red probe on the base terminal (use Google if you don't know which one that is, package type is SOT-23), then with the black probe on either the collector or emitter terminals, the meter should show approx. 0.65 - 0.7V across either of the two junctions.  In this case you can measure the transistors in circuit without removing them.

Most electronics parts suppliers will carry 2N3904 (also known as MMBT3904), they're one of the most common small signal transistors on the planet.  Or you should be able to substitute with most equivalents such as BC847, 2N2222, etc.

If you're feeling lazy, and in the very high probability you're not using a modem that relies on the ring indicator signal, just remove Q571 near the serial port and use that as the replacement transistor.  You'll need to find out which is the defective transistor as mentioned above to know which one to replace.

I'd check voltages first. Bet one is lower than is should be. If I recall, on Q transistors. Output should read around 2.2v - 2.3v if working ok.

[F0LLETT]

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

The Q transistors will not be bad. As your getting Red Green Blue fine (look at your pic, the tick has all 3 colours). Its just something is causing a voltage issue, lowering the colour on one of them.
For me, it was fluid from cap leakage causing short under sony chip.

Measure voltage from ground point of board and the positive on the 3 different transistor legs.

[F0LLETT]

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

It should not have gone worse. Unless there is track damage from leakage.
Also, how did you read voltages, as -v is not right. Even if faulty, no way they would all be -v.

[F0LLETT]

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

Check the voltages on the Q components. As I think you were reading them wrong.
Measure from board ground, then positive on each pin of Q components.

[F0LLETT]

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

Glad you got to bottom of it.