Part swap and Laser adjustment for CDROM

I spent the last couple nights trying to restore a problem NeXT CDROM drive. This particular unit had bent internals and a badly damaged logic board from leaking caps. I managed to score an AppleCD 150 from eBay for under $30 which I used for donor parts. It also was not working. The drive in the AppleCD is a -very- close match for the NeXT but has a few small differences to the internals. The chassis and faceplates are a perfect fit for each other. The ROMs are not compatible, which is a bummer because I hoped that I could have the drive report exactly as it was in the NeXT. The Apple ROM luckily seems to be fully compatible with nextstep. So first thing was to replace all the caps in the Apple drive. Unfortunately the unit would still not read disks. As it turns out the laser assembly was bad. So I removed it from the NeXT drive and swapped it to the Apple. This part is a perfect match. It would now read, but not reliably even after cleaning the lens. I figured there was probably a calibration issue with the laser, but couldn't find a free service manual. After reading up on drive repair tutorials from game consoles I figured out that the typical repair is to decrease the resistance on the pot for the diode. I took a reading of 700 ohms on a good laser. I found that at 600 ohm the drive started reading disks fine. It was then just a matter of replacing the front panel bezel and circuit board from the NeXT to the Apple. I now have a perfectly working drive. To adjust the pot for the laser it is not necessary to pull the drive apart. There is an access panel on the bottom that exposes the laser assembly. Use a pair of small pliers to -gently- turn the pot from the side. Move it just a hair at a time and check the resistance across. I'd say test in 50 ohm increments. Hopefully this saves someone some time in the future.

--
Brian

As a follow up to this, I've found an additional DEC drive (RRD42-AA) which is also a rebranded Sony. It seems to be an exact match for the next drive. I'm keeping a running list on my site:

http://www.asterontech.com/Asterontech/next_cdrom_refurb.html

--
Brian

Quote from: "barcher174"As a follow up to this, I've found an additional DEC drive (RRD42-AA) which is also a rebranded Sony. It seems to be an exact match for the next drive. I'm keeping a running list on my site:

http://www.asterontech.com/Asterontech/next_cdrom_refurb.html

--
Brian

Hello Brian: Awesome Work ! Best Regards Rob

It's interesting, I've done two (unsuccessful) re-caps on caddy-style Toshiba XM-3301BME drives. These are essentially the first internal CD-ROM's to be part of the PS/2 series; most often found in Model 57's and 95's.  They have square plastic surface-mount capacitors, all of which have failed and spread their fluid on the boards. (Below is a picture of a board before repair attempt.) I have a feeling that this fluid may be conductive, which explains the two failures -- the bigger caps near the DC-in area at the top right exploded.

But if I had been successful on either one, I wondered if I would faced of re-calibrating the laser and other components... perhaps an impossible task without the original Toshiba calibration disc and extensive instructions...

(https://flic.kr/p/FCksMs)

You can probably get away with no calibration after repairing the logic board. At a glance I would suspect some of those VIAs have been eaten away and need to be repaired. Are these the same Toshiba drives that used the nylon gears that would strip? I remember hating that :D

I have found the full schematics for the Sony CDU-7205 Drive. This drive uses a custom sony interface (looks like IDE?) and is about a 90% match for the NeXT drive. At any rate, this should be super helpful when trying to track down issues.

http://www.asterontech.com/Asterontech/next_cdrom/Sony_CDU-7205_SCHM.pdf

I did some more work with the DEC drive today and I can now confirm the hardware to be a 100% match for the NeXT CDROM drive. This includes cross compatibility with the ROMs, meaning you can swap between the units. The DEC unit contains DEC software branding, so if you're a purist you can flash with the original NeXT ROM. I will update my site with the ROMs for each.

I confirmed the AppleCD SC Plus to be a NeXT compatible Sony drive today. Site updated with the Apple ROM.

http://www.asterontech.com/Asterontech/next_cdrom_refurb.html

I can confirm a sun 411 CDROM drive with a CDU-8012 is hardware compatible. I had previously assumed it was a different mechanism due to the difference in front faceplate. I have updated my site.

I installed my original cube OS back when I owned a cube using an external Sun CD in a 411 case from a Sparcstation LX.