CD-ROM2 missing cap at (C158)

[SlightlyObsessed]

I have been working on a CD-ROM2 unit and discovered a missing component at C158. I've looked around for documentation that would help me identify what to replace it with but so far have turned up nothing.

One of the C158 pads is ground the other connects to pin 33 of the NEC D78C14GF which appears to be "AN5" according to the data sheet.

Any ideas what component should be there?

I've been fighting random audio dropouts with this board and wondering if it's related to this missing cap/component.

Thanks!

[gtsamour]

Here... I don't see a C158 cap in the schematic though....

https://console5.com/wiki/Turbo_Grafx_CD-ROM_Drive

Is it an SMD cap component? Could you post a picture?

Audio dropouts could be due to the caps being old, you may need a total cap replacement.

[SlightlyObsessed]

Yes it's a surface mount one. This isn't the best image, but it's what I have at the moment. You can see something was in that space and broke loose at some point.

As an update to the audio, I did manage to fix the drops and everything else seems to be working fine now despite the missing cap. It would be nice to replace it anyway though. This drive got a good once over, complete cap replacement (not including the SMD ones obviously), pot adjustment and gear/rail cleaning, overall cleaning, middle gear inspection etc. (The image below is prior to any work) the audio drops ended up being a mechanical issue with the worm gear and laser rail. (Which was previously cleaned and re-greased but running out of other ideas I did it again as well as turned the rail around.)

[gtsamour]

Yes you're right, I can see a cap there from pictures of my board but I have no idea of what value. There are no indications on it.

Maybe an expert could shed some light on that one....

[Keith Courage]

I have a bunch of spare boards. Meaning I could always just de-solder said cap from one of them and send it to you.

[SlightlyObsessed]

Keith Courage- that's mighty nice of you! Would you be willing to part with the whole board (I'd be willing to pay you for it). Reason I ask is that this one has some oddities, maybe these components are stock or are part of some repair, I've not seen enough of these to know. I've been meaning to start another thread asking but here goes:

Do these look Factory or are these part of someone's "mod/repair" ? Doesn't look "factory" to me and viewing online images, I never see these components. I've even tried removing all of them and found the drive still functions fine with everything I've thrown at it...more of a curiousity at this point.

Mounted transistor with diode, both outer legs connect to the 5v supply, the inside leg goes to that trace that leads to a via and ends on the NEC D9309GF chip (can't recall the exact pin but there's no data sheet for the chip that I could find.)




and the cap across VR103 pot....

[Keith Courage]

Those are all factory parts but I have no idea why some of these drives have them and some do not. I believe it depends on the revision of the board. There were two types made for the white pce cd rom.  For the same reason some of these boards have grounding wires that go to the grounding plates and some simply have a springy type connection to the grounding plate with no soldering needed.

I have removed the yellow part in your pic that connects the contacts on that black potentiometer in a few CD drives.  I have no idea why but this can sometimes fix lens reading issues. Not sure if the part simply goes bad or why it works but it does sometimes.

One good thing about the board you have is I have yet to come across one that has needed the capacitors changed out. The bad thing about the board is that it's a PITA to change the caps if you ever wanted to do preemptive maintenance with this board compared to the other revision.

[SlightlyObsessed]

Good to know! I'll put back the transistor at least, happy to know those are original additions. My laser is reading beautifully thanks to a scope and some dialing, so I'll probably leave off the yellow cap across the tracking gain pot. As far as the caps go, I did already replace all the electrolytic caps, it's tedious but personally didn't find it too bad, mileage may vary of course. Anyway about that missing SMD cap (C158), if you're still willing to send it along that would be great, I'd be happy to put it on the capacitance tester and post so the information gets out there (in the unlikely event someone else is missing this cap, too bad there are no schematics...one component at a time will get us there eventually i suppose)

[Keith Courage]

Just PM me your address.

[SlightlyObsessed]

PM sent, thank you!

[SlightlyObsessed]

Special thanks to Keith Courage for supplying the missing SMD cap! I removed it from the donor board and tested it at 53nF. (In the very unlikely event someone is missing the same cap or would like to know the value) Missing cap replaced and everything is in great working order!