Welcome, Guest. Please login or register.

Author Topic: A600 recapped but now with colour issues  (Read 5264 times)

Description:

0 Members and 1 Guest are viewing this topic.

Offline swood123Topic starter

  • Newbie
  • *
  • Join Date: Feb 2024
  • Posts: 22
  • Country: gb
    • Show only replies by swood123
A600 recapped but now with colour issues
« on: December 02, 2024, 10:14:22 PM »
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
 

Offline Boing-ball

Re: A600 recapped but now with colour issues
« Reply #1 on: December 02, 2024, 11:31:19 PM »
I don’t think the problem is with the capacitors. The issue will be either a bad trace or acid damage from the leaking caps. You did clean down the board with Isopropyl Alcohol or contact cleaner? Check the chip pins and traces around U42 as they look a little bit dull. If it were me, I would have kept the RF modulator out, unless you are keeping the machine as authentic as possible.
 
The following users thanked this post: swood123

Offline Castellen

Re: A600 recapped but now with colour issues
« Reply #2 on: December 03, 2024, 05:24:02 AM »
I'd agree, that specific issue is often caused by one of the RGB buffer transistors damaged by the capacitor electrolyte.  Given they're only a few cents each, just replace all 3 of them, Q231, Q232, Q233.  Else you could measure where the R, G or B signal is going missing.
 
The following users thanked this post: swood123

Offline F0LLETT

  • Amigakit / A-EON Support
  • Administrator
  • Hero Member
  • *****
  • Join Date: Aug 2007
  • Posts: 1000
  • Country: gb
  • Thanked: 84 times
  • Gender: Male
    • Show only replies by F0LLETT
    • Ultimate Amiga
Re: A600 recapped but now with colour issues
« Reply #3 on: December 03, 2024, 09:12:29 AM »
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.
Quote from: Hungry Horace
Resolute and Industrious Grand ruler of the yellow people and the Ultimate Amiga Empire
Ultimate Amiga Network (Home of SONY PSP Amiga Emulator and AMOS Factory)

Quote from:  He who shall not be named
"Chris is that you!!!"
My all time favorite quote.
 
The following users thanked this post: swood123

Offline swood123Topic starter

  • Newbie
  • *
  • Join Date: Feb 2024
  • Posts: 22
  • Country: gb
    • Show only replies by swood123
Re: A600 recapped but now with colour issues
« Reply #4 on: December 03, 2024, 09:16:35 AM »
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
 

Offline swood123Topic starter

  • Newbie
  • *
  • Join Date: Feb 2024
  • Posts: 22
  • Country: gb
    • Show only replies by swood123
Re: A600 recapped but now with colour issues
« Reply #5 on: December 03, 2024, 09:18:23 AM »
Excuse my ignorance but can you confirm which one is the Sony chip?

 

Offline Boing-ball

Re: A600 recapped but now with colour issues
« Reply #6 on: December 03, 2024, 09:29:41 AM »
Excuse my ignorance but can you confirm which one is the Sony chip?

I’ll stick my neck out and say U12? The one near the IDE connector.
 

Offline F0LLETT

  • Amigakit / A-EON Support
  • Administrator
  • Hero Member
  • *****
  • Join Date: Aug 2007
  • Posts: 1000
  • Country: gb
  • Thanked: 84 times
  • Gender: Male
    • Show only replies by F0LLETT
    • Ultimate Amiga
Re: A600 recapped but now with colour issues
« Reply #7 on: December 03, 2024, 09:34:35 AM »
Excuse my ignorance but can you confirm which one is the Sony chip?

U12
Quote from: Hungry Horace
Resolute and Industrious Grand ruler of the yellow people and the Ultimate Amiga Empire
Ultimate Amiga Network (Home of SONY PSP Amiga Emulator and AMOS Factory)

Quote from:  He who shall not be named
"Chris is that you!!!"
My all time favorite quote.
 

Offline swood123Topic starter

  • Newbie
  • *
  • Join Date: Feb 2024
  • Posts: 22
  • Country: gb
    • Show only replies by swood123
Re: A600 recapped but now with colour issues
« Reply #8 on: December 03, 2024, 10:31:50 AM »
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
« Last Edit: December 03, 2024, 10:53:50 AM by swood123 »
 

Offline Castellen

Re: A600 recapped but now with colour issues
« Reply #9 on: December 03, 2024, 07:06:31 PM »
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.

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.
 
The following users thanked this post: swood123

Offline F0LLETT

  • Amigakit / A-EON Support
  • Administrator
  • Hero Member
  • *****
  • Join Date: Aug 2007
  • Posts: 1000
  • Country: gb
  • Thanked: 84 times
  • Gender: Male
    • Show only replies by F0LLETT
    • Ultimate Amiga
Re: A600 recapped but now with colour issues
« Reply #10 on: December 04, 2024, 09:39:58 AM »
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.
Quote from: Hungry Horace
Resolute and Industrious Grand ruler of the yellow people and the Ultimate Amiga Empire
Ultimate Amiga Network (Home of SONY PSP Amiga Emulator and AMOS Factory)

Quote from:  He who shall not be named
"Chris is that you!!!"
My all time favorite quote.
 
The following users thanked this post: swood123

Offline swood123Topic starter

  • Newbie
  • *
  • Join Date: Feb 2024
  • Posts: 22
  • Country: gb
    • Show only replies by swood123
Re: A600 recapped but now with colour issues
« Reply #11 on: December 04, 2024, 09:32:03 PM »
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




 
 

Offline F0LLETT

  • Amigakit / A-EON Support
  • Administrator
  • Hero Member
  • *****
  • Join Date: Aug 2007
  • Posts: 1000
  • Country: gb
  • Thanked: 84 times
  • Gender: Male
    • Show only replies by F0LLETT
    • Ultimate Amiga
Re: A600 recapped but now with colour issues
« Reply #12 on: December 04, 2024, 10:32:00 PM »
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.
« Last Edit: December 04, 2024, 10:32:45 PM by F0LLETT »
Quote from: Hungry Horace
Resolute and Industrious Grand ruler of the yellow people and the Ultimate Amiga Empire
Ultimate Amiga Network (Home of SONY PSP Amiga Emulator and AMOS Factory)

Quote from:  He who shall not be named
"Chris is that you!!!"
My all time favorite quote.
 
The following users thanked this post: swood123

Offline swood123Topic starter

  • Newbie
  • *
  • Join Date: Feb 2024
  • Posts: 22
  • Country: gb
    • Show only replies by swood123
Re: A600 recapped but now with colour issues
« Reply #13 on: December 10, 2024, 08:26:24 PM »
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
         
« Last Edit: December 10, 2024, 08:27:35 PM by swood123 »
 

Offline F0LLETT

  • Amigakit / A-EON Support
  • Administrator
  • Hero Member
  • *****
  • Join Date: Aug 2007
  • Posts: 1000
  • Country: gb
  • Thanked: 84 times
  • Gender: Male
    • Show only replies by F0LLETT
    • Ultimate Amiga
Re: A600 recapped but now with colour issues
« Reply #14 on: December 11, 2024, 08:59:26 AM »
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.
Quote from: Hungry Horace
Resolute and Industrious Grand ruler of the yellow people and the Ultimate Amiga Empire
Ultimate Amiga Network (Home of SONY PSP Amiga Emulator and AMOS Factory)

Quote from:  He who shall not be named
"Chris is that you!!!"
My all time favorite quote.