SCPH-102 (PSOne) - Laser assembly not responding to anything.

I have this PSOne (SCPH-102) that i have been trying to repair for a while now with no result. At first it seemed to have a common dying laser (game discs were rarely being read, only audio discs worked etc'), but recently it became worse as now no laser assembly that i put in it responds; when i use one (such as the brand new KSM-440BAM i got), the PS1 doesn't ever even spin the disc at any given point.

The unit in question has a mod-chip that i assume is correctly installed (before anything happened, i was able to launch backups whenever the old assembly didn't give) and i did double check the new 440BAM with another (functional) identical unit i have - it works great. Also i did check the motor cable (the black and white one), it was properly connected and i did messure a charge while using it with the new assembly (it also worked fine in my other functional unit too).

By this point i'm starting to think that during my previous tinkering, i accidentaly managed to frag either an IC or a bunch of resistors that were connected somehow to the CD-Drive flex cable port.
Unfortunatly, i don't have any idea about how to troubleshoot this and couldn't find any hints online. By this point i am pretty much shooting blind based on whatever service manuals i find.. which doesn't really get me anywhere.

Anyway, i could really use some help; If anyone has an idea of what might be the problem, i'll be thankful if you do please let me know.

EDIT (Update):
For anyone who happened to find this post in search for a solution, the problem was indeed caused by a bad fuse located at PS601 (marked in red). Replacing it with a new 800mA 32V SMD fuse fixed the problem, the unit works fine now.

 

Make a photo so we can help you, plus a first thing to do is check the fuses

 

Photos are great, if you can

Out of curiosity where did you get the brand new KSM-440BAM?

 

@master991 I kind of get disoriented when i look at the schematics or the motherboard itself.. would you mind pointing out where to look exactly (marking it on the photo bellow could be a good idea)?
The unit itself boots fine btw (i see the menu and everything), it just seems like the drive itself is either not responding or is not getting detected in the first place.

@ShaneMcRetro It's one of these chinese "clones" you can find on eBay if you know how to pick a good seller. From what i tested so far it does a great job compared to an old original 440BAM, the spindle seems to be well made too.

Not sure how they can help, but here are the photos of the defective unit: http://imgur.com/a/Olk5y
Sorry in advance for my sloppy camera work, if anything looks too unclear let me know and i'll try taking a better photo.

 

are you testing the laser with case on or off?

 

@psydefx Tried with it both on and off on the defective unit, didn't nudge eitherway. The same laser worked pretty much straight away on the other PS1 i have though (all i did was plug it in and it worked).

 

ah. just that i know the modchip makes the metal shield abit higher and it can mess up the close switch
when i installed a mm3 in my scph-101 i found that out

 

The fuses are that black rectangular thing looking at the lower left of the photo that you have posted.
They have marked the number "20" on them. You have thest the continuity with a multimeter.
You should check also the lid switch. It's the black one on the lower right.

 

Depends on what chip you use and where you put it.

 

I checked the fuses, looks like out of all 4 of them the one located on PS601 (the lowest one in my photo) is giving a weird reading (lower voltage on output). Further digging in the schematics, i found out that the trace from this fuse is actually directly leading to pin 10, 19 (POW-VCC) and 28 (PRE-VCC) on IC722 (the Panasonic AN8732SB controller), so i guess this does seem like a possible source for the problem.

Anyway, i have no idea how i'm going to replace the fuse right now as i don't have fuses this small anywhere. Do you think it's posstible to bypass it somehow without leaving the entier thing at too much risk?

p.s
Checked the lid switch too, it works fine.

 

I don't understand very well, i'm sorry, but if i've understand you have reading a very low voltage across the fuses? If so, even the fuse is blown it's normal read little voltage on the "output" of the fuse.
You should tested the continuity beetwen the fuses, not measuring the voltage (you must use the multimeter continuity function).

You should never bypass a fuse, maybe there's a short somewhere...

 

@master991 Sorry about that, sometimes my english gets easily misunderstood when i write stuff.
What i meant to say is that i also messured for voltage as to check if there was anything passing through at all and found out that there was a lower value on the "output" end (the one leading to the IC), which might be causing the chip to be underpowered or something.
Eitherway, I did the continuity test too and it didn't pass with that fuse (the multimeter didn't beep or show anything on screen).

Also by bypassing i didn't mean directly, as in removing the fuse and connecting the two ends. My thought was to use a trace from a working fuse (or possibly an external one) by connecting it to the trace beind the problematic fuse - as in doing something like this (bad fuse marked in red).
I know it's risky, but i don't have much options right now and just want to confirm that this is the source of the problem. Would you say it will be a better idea to not touch it until i can find a replacement?

 

It's not a properly fix \ workaround because if the fuse is rated to 20ma you will end absorbing more than it's designed (for example 30ma) and it will blown. You can try as last desperate choice but it's not the best option (better than bridge). You need to search, IRC, a 0.8A smd fuse...

You must forgive me for my bad english, i'm very sorry for this...

 

@master991 Don't worry it's fine , if anything sorry for my written english being a bit weird to read. You really helped me out so far, now i have a better direction with this.

I have one more question, a fuse that is rated with 0.8A at 32V (or greater) should work fine right?
For example, if i get something similar to this fuse only with an "FB" or "F" marking (like these once), should it do the trick?

 

yeah, a greater voltage rating does not cause any problems. You can use them without any trouble (they can be bigger in dimension, but they are ok)