trashedcabs
Grand Master
I've repaired 15 GDROM drives this year and had 100% success rate so I figured I would post my notes somewhere.
To swap the laser assembly for testing, instead of trying to plug the cable in while it's mounted to both rails I have found it easiest to remove the white plastic stopper holding the worm gear rail and take the whole thing out. This way, you can plug the flex cable straight in without bending or risk of damaging it.
Symptom: Shorted power rails
Someone plugged power in backwards and blew up the motor controller BA5986FM. Replace this chip and the short should go away.
Symptom: Error 24
Assuming your DIMM, disc, and cable are known good, this seems to boil down to a laser issue where the sensor is not returning any data at all. Swapping the laser has been the fix for me, however this is also a less common error than error 25 in my experience. Lasers can be sourced from a handful of Samsung CD drives. There are some specific models with the exact laser assembly as well--no modification needed.
Symptom: Error 25
Almost every drive I've repaired has had this error. This is a super generic drive error that seems to mean "too many read errors" and paying attention to what the drive is doing can help you determine the cause.
During a good startup sequence, the head should seek to the inside while spinning slowly. Next the head will jump around a little, then the disc should go to full speed and the head will scan back and forth a few times before booting and you should get a "-- NAOMI GDROM SYSTEM --" message on the screen.
1. If the disc spins slowly for a short bit, then stops: it might be a laser issue. Lubricate everything and clean the lens thoroughly. If the gears and rails are dirty or gummed up from previous grease, it can also slow reads enough to cause errors.
For a quick and dirty fix attempt you can try reducing the current limiting pot resistance, but too low for too long will kill the laser. If you need to reduce the resistance very far down then your caps on the main board are likely bad. I had one drive where I needed to reduce the pot way down to 300ohm for it to read reliably, but after replacing all the 100uF caps on the board I was able to increase the pot up to 700ohm and still get reliable reads. I'm assuming power delivery to the laser is compromised by failed caps, as he 100uF caps seem to go bad on almost all of these units.
One other thing is to check and ensure the pot is actually changing as you turn it. I had two units where the previous owner broke the pot and it was always reading 3.3kohm, and replacing the pot fixed the issue.
I've also had a couple units where the flex cable from the board to the laser assembly had failed causing this as well. Check the cable for any tears or sharp bends from previous repair attempts. The units I fixed with this issue all had multiple Chinese service stickers on them and looked like they were pulled from the ocean.
2. If the disc spins fast and seems to pulse slower sometimes as if it's trying to start, then the laser is likely good and your bottom controller board likely has bad caps. I had one unit like this solved by replacing the 100uF caps. If you have a known good laser, try swapping it in first. If it does the same thing, then it's probably caps.
3. If it doesn't spin at all, then either the motor controller, caps, or the SCSI cable/connector are bad. The drive will not spin up unless it can communicate with the DIMM.
I'm sure there are more issues than that, but this has covered all the issues my batch of drives has had. Keep repairable hardware out of landfills.
To swap the laser assembly for testing, instead of trying to plug the cable in while it's mounted to both rails I have found it easiest to remove the white plastic stopper holding the worm gear rail and take the whole thing out. This way, you can plug the flex cable straight in without bending or risk of damaging it.
Symptom: Shorted power rails
Someone plugged power in backwards and blew up the motor controller BA5986FM. Replace this chip and the short should go away.
Symptom: Error 24
Assuming your DIMM, disc, and cable are known good, this seems to boil down to a laser issue where the sensor is not returning any data at all. Swapping the laser has been the fix for me, however this is also a less common error than error 25 in my experience. Lasers can be sourced from a handful of Samsung CD drives. There are some specific models with the exact laser assembly as well--no modification needed.
Symptom: Error 25
Almost every drive I've repaired has had this error. This is a super generic drive error that seems to mean "too many read errors" and paying attention to what the drive is doing can help you determine the cause.
During a good startup sequence, the head should seek to the inside while spinning slowly. Next the head will jump around a little, then the disc should go to full speed and the head will scan back and forth a few times before booting and you should get a "-- NAOMI GDROM SYSTEM --" message on the screen.
1. If the disc spins slowly for a short bit, then stops: it might be a laser issue. Lubricate everything and clean the lens thoroughly. If the gears and rails are dirty or gummed up from previous grease, it can also slow reads enough to cause errors.
For a quick and dirty fix attempt you can try reducing the current limiting pot resistance, but too low for too long will kill the laser. If you need to reduce the resistance very far down then your caps on the main board are likely bad. I had one drive where I needed to reduce the pot way down to 300ohm for it to read reliably, but after replacing all the 100uF caps on the board I was able to increase the pot up to 700ohm and still get reliable reads. I'm assuming power delivery to the laser is compromised by failed caps, as he 100uF caps seem to go bad on almost all of these units.
One other thing is to check and ensure the pot is actually changing as you turn it. I had two units where the previous owner broke the pot and it was always reading 3.3kohm, and replacing the pot fixed the issue.
I've also had a couple units where the flex cable from the board to the laser assembly had failed causing this as well. Check the cable for any tears or sharp bends from previous repair attempts. The units I fixed with this issue all had multiple Chinese service stickers on them and looked like they were pulled from the ocean.
2. If the disc spins fast and seems to pulse slower sometimes as if it's trying to start, then the laser is likely good and your bottom controller board likely has bad caps. I had one unit like this solved by replacing the 100uF caps. If you have a known good laser, try swapping it in first. If it does the same thing, then it's probably caps.
3. If it doesn't spin at all, then either the motor controller, caps, or the SCSI cable/connector are bad. The drive will not spin up unless it can communicate with the DIMM.
I'm sure there are more issues than that, but this has covered all the issues my batch of drives has had. Keep repairable hardware out of landfills.