Problems adding Digital Out to Laserdisc player (LC78621 chip)

Hybrid fourdoor · 12th February 2005, 10:25 PM

Trying to add a digital output to a Laserdisc player. The datasheet for the chipset says pin 56 is DOUT. So I ran a wire from pin 56 to a TTL=>Coax circuit, however when I use a multimeter the voltage coming from the chip is only like 2.9V....shouldn't it be ~5.00V?

Needless to say I'm not getting any output.

I didn't do anything to the chip, as I don't see like a DOUT enable pin or anything.

Any ideas?

inn · 25th February 2005, 03:46 AM

hi, you may try the following which I have done to my Onkyo LD player.

LC78621 75ohm coax CS8412/4
pin56-DOUT ---------------------------> pin9-RXP
common gnd ---------------------------> pin10-RXN
(find any gnd jumper next to LC78621)

I suppose you must have missed out the gnd

Jocko Homo · 25th February 2005, 05:37 AM

Yes. For starters:

You can't measure a digital signal, probably 2.8 MHz or so, with a multimeter.

Jocko

A 8 · 25th February 2005, 07:13 AM

Quote:

the voltage coming from the chip is only like 2.9V....shouldn't it be ~5.00V?

It would probably be something like that measured by a multimeter even if it was working so it really don't indicate anything.

Dout can be muted, details in the datasheet. The other issue could be how you've connected things, dout is made to drive a transformer direct again see the datasheet.

inn · 26th February 2005, 01:59 AM

Quote:

Originally posted by A 8
Dout can be muted, details in the datasheet. The other issue could be how you've connected things, dout is made to drive a transformer direct again see the datasheet.

hi A8, do you mind sharing how could I disable the MUTE function in this chip....I know very little in digital world

Thanks in advance!
PS : I connected the DOUT to CS8414 via 1:1 Pulse Trans in my external DAC.

A 8 · 26th February 2005, 07:43 AM

inn,
I know you can read, its in the datasheet. If you cant find it just do a search for dout.
/Michael

Hybrid fourdoor · 26th February 2005, 12:10 PM

Quote:

Originally posted by A 8

Dout can be muted, details in the datasheet. The other issue could be how you've connected things, dout is made to drive a transformer direct again see the datasheet.

Heres the inspiration I used. The only thing I could think of was the mute pin.

A 8 · 26th February 2005, 03:15 PM

Quote:

Heres the inspiration I used. The only thing I could think of was the mute pin.

The datasheet says 0.5vpp for dout so it is probably too low for your 74hc04 to detect any pulses.
For testing you could connect dout via a cap directly to spdif in and see what happens.

inn · 27th February 2005, 05:57 AM

why do you need 74hc04 in the first place?
I connected the DOUT from LC78621 with coax cable directly to my digital receiver CS8414 via a 0.1uF wima mkp cap and 1:1 pulse trans (all in my DIY DAC). No problem with the output level.

coax
LC78621 pin56 (Dout) --------->0.1uF---->pulse trans--->cs8414
LC78612 gnd -------------------->DAC gnd
coax schield

lumanauw · 30th January 2009, 08:30 AM

I'm trying to make digital SPDIF out for a Denon CD player. This unit has no SPDIF or Optical digital out.

The IC is LC78621.

From the scope I see pin56 (Dout) is giving nothing, 0V.

How can I enable Dout to give digital out? I cannot understand post by A8 above.

12th February 2005, 10:25 PM	#1
Hybrid fourdoor diyAudio Member Join Date: May 2003 Location: Ft. Worth, TX	Problems adding Digital Out to Laserdisc player (LC78621 chip) Trying to add a digital output to a Laserdisc player. The datasheet for the chipset says pin 56 is DOUT. So I ran a wire from pin 56 to a TTL=>Coax circuit, however when I use a multimeter the voltage coming from the chip is only like 2.9V....shouldn't it be ~5.00V? Needless to say I'm not getting any output. I didn't do anything to the chip, as I don't see like a DOUT enable pin or anything. Any ideas? __________________ I enjoy my organic shapes.....

25th February 2005, 05:37 AM	#3
Jocko Homo Banned Join Date: Feb 2002 Location: As far from the NOSsers as possible	Any ideas? Yes. For starters: You can't measure a digital signal, probably 2.8 MHz or so, with a multimeter. Jocko

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25th February 2005, 03:46 AM	#2
inn diyAudio Member Join Date: Dec 2004 Location: singapore	hi, you may try the following which I have done to my Onkyo LD player. LC78621 75ohm coax CS8412/4 pin56-DOUT ---------------------------> pin9-RXP common gnd ---------------------------> pin10-RXN (find any gnd jumper next to LC78621) I suppose you must have missed out the gnd

26th February 2005, 07:43 AM	#6
A 8 diyAudio Member Join Date: Mar 2003 Location: Gothenburg	inn, I know you can read, its in the datasheet. If you cant find it just do a search for dout. /Michael

27th February 2005, 05:57 AM	#9
inn diyAudio Member Join Date: Dec 2004 Location: singapore	why do you need 74hc04 in the first place? I connected the DOUT from LC78621 with coax cable directly to my digital receiver CS8414 via a 0.1uF wima mkp cap and 1:1 pulse trans (all in my DIY DAC). No problem with the output level. coax LC78621 pin56 (Dout) --------->0.1uF---->pulse trans--->cs8414 LC78612 gnd -------------------->DAC gnd coax schield

30th January 2009, 08:30 AM	#10
lumanauw diyAudio Moderator Emeritus Join Date: Oct 2002 Location: Bandung	I'm trying to make digital SPDIF out for a Denon CD player. This unit has no SPDIF or Optical digital out. The IC is LC78621. From the scope I see pin56 (Dout) is giving nothing, 0V. How can I enable Dout to give digital out? I cannot understand post by A8 above.

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