Schematics for NEC 602 CDROM Drive?

[fastcat95]

Hello!

Does anyone out there have schematics, or know of a
source of them, for the NEC 602 (6XE) CDROM drive. I
have gone in circles with NEC in the USA trying to find
a department that might have them. Any help would
be much appreciated!

fastcat

[mlloyd1]

good luck. I bought a few of these on ebay a while back. I gave up on getting schematics from NEC or anywhere else.

if the CDRom units weren't built so well, I'd really be ****ed ...

mlloyd1

edit:
hmmm... interesting SW. I used the word that begins with "p" and a pair of "s"

[randytsuch]

I would be interested if you found one too. I just got one, and will probably end up buying another, so I have one to listen to, and one to tweak. Gives me a spare too. For the price, no reason not to.

If you search over at audioasylum, you can find some posts of people who have tweaked the NEC, but nothing too drastic was done to it.

Randy

[jonclancy]

I've just bought one of these drives on eBay for the princly sum of 12.50USD (7.47GBP). Add a few USD on for postage and that is one inexpensive experiment. I have been over to AA and copied any references to tweaks that I found there. I'm intending to run it with a DacKit or DDDac (will be building both and am halfway through the DacKit).

If I find any further tweakage, I'll post here.

Cheers

Jon

[jonclancy]

Hi All,

I had my 602 open last night and had to take the 502 inside apart!!

What nice engineering!! I stuck the tack on the cans and stripped the caps. All back together and working fine. I am listening at the moment, through Scott Nixon's DacKit and it sounds very nice indeed!! In fact, almost as good as when I use my 600UKP Arcam as a transport. I can't say if the mods have made any improvement though. Before I bunged it all back together, I listed the ICs on the mainboard. Here they are:

IC101 BH9595FP 545 186Y
IC115 NEC D7225G A9542EP024
IC122 NEC D78330GJ 9537MK002
IC123 SONY CXD1808AQ 536H10E CDROM DECODER
IC124 XLJ6265AF-10LL 543 166
IC128 NPNX NN514256J-45 943 A74222
IC129 NPNX NN514256J-45 943 A74222
IC130 SYMBIOS 53CF92A
IC302 SONY D2559Q 531D83E
IC501 ST B88CB 9535CS (N513A)
IC701 SONY CXA1610M 538D09K
IC702 SONY CXD2510Q 536D52E
IC703 SONY CXA1373AQ 545MB4V
IC711 TA 8407F 9538K
IC712 TOSHIBA TA8192F 9543K MOTOR DRIVER IC
IC719 BA7082F 543 190

I can't find the datasheet for the CXD1808AQ - I would like to see if that is where I can tap the digital signal before it becomes 5v TTL. I am amazed it sounds so good, seeing as the cdrom digital out wires just wander for miles around the back of the mains transformer!!

Anyone got any further with the mods?

Jon

[fastcat95]

Hello!

As to NEC 602 mods...

The best ones involve building a totally
analog +5 & +12 VDC power supply

Adding some sort of SPDIF output buffer
(either 74VHC04 and/or pulse transformer)

BNC true 75 ohm output jack

Case/drive/chassis damping

Replacing any small onboard electrolytics
with better units where they will fit

Isolation foot system under the drive housing

Vents for better air circulation inside the drive
(ever notice how WARM the CD caddy gets after
an hour or two of playing?)

The power supply & output interface upgrades
are probably the most productive, and DO
really improve the sonics of this CDROM drive.

Enjoy!

fastcat

[jonclancy]

Hi Fastcat,

thanks for the ideas. I saw the SPDIF buffer on a link posted in another thread (loads of options here: http://www.andrewkilpatrick.org/mind/spdif/#faq ).

Looks like they are simple enough for even me to do!!

I have a plan for the power supplies (super-regulated), and I want to use those I construct in later projects.

The 75 ohm output should be a doddle. I will have a look at the board in the back of the main case (just near the transformer), because that may well have a reasonable TTL / SPDIF circuit on it that can be upgraded.

I have just obtained another from eBay at the massive cost of 5 UKP(!!), so I'll have a reference. I'll be interested to see what we can do with this kit!!

Cheers

Jon

[fastcat95]

Jon:

When you were looking around inside the NEC 602,
did you notice what chip was outputting the TTL +5V
SPDIF signal, and if there was any sort of attempt in
the output circuit to get the proper 75 ohm output
impedance? Or did the wires simply come off the
rear internal connector and go to the RCA with no
output circuit or 75 ohm impedance matching?

Thanks!

Fastcat

[jonclancy]

Hi Fastcat,

I'll have a look. I don't seem to recall a 75R smd resistor near the TTL. It may be on the small board at the back of the external casing.

I'll be opening up my new reference 6Xe (5 GBP - eBay. Next will be free? ), and will take some digisnaps.

Cheers

Jon

[fastcat95]

Jon:

Since you will be looking at the inside of another
602 unit, can you tell which of the chips that
you listed in a posting is the one outputing the
TTL digital signal? There is always the issue of
the chips ability to put out sufficient current for
the resistor network (330/100 ohm) that sets
a correct 75 ohm output impedance.

All this is assuming that there are no digital
output resistors currently in the NEC that DO set
the 75 ohm impedance (previous posters on
another website seem to think that there are
NO resistors present). I have not yet torn down
one of my NEC transports to verify this. Posting
digital snapshots sounds like a good idea!

Fastcat