Lexicon 480L Schematic Required...

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Swedish Chef

Well-known member
Joined
Jun 7, 2004
Messages
351
Location
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Anyone got one? :sad:
I have a sick one and Harman are unsurprisingly useless. They told me to buy a new card that I know is not the one with the problem :evil:

Any help greatly appreciated!

Cheers

chef
 
[quote author="jensenmann"]...and I could need a Larc schemo. The meter is fucked up and shows 0dB all the time.
:guinness:[/quote]
... and my LARC always has blinking "overs" with no signal ...
 
I have a 480L that had problems. I sent the problem card to harman and got a new one for 250.00(us) not bad considering I use it all the time. I have seen the repair manual not much really in there other then schemo's for the PSU section andf how to set that up. @ lexicon they put in new(nos) DSP chips and fixed my problem of digital noise on one card. IT would randomly appear and go away and oscilate on and off. at the time I didn't really know what to do other then back to the shop. was totally worth it. they may have even given me a referb card in exchange for my card I don't remember.
 
cheers lads!
Pucho812: that's interesting. Harman over here have been pretty useless so far, but perhaps I'll persist :sad:
I'll let you know how I fair... :green:

chef
 
In my case I narrowed it down to an HSP one of the 2 DSP cards in the unit. When I did that, I sent that board off the Lexicon for repair. I am suprised they would want to sell you a new one as from my understanding they are no longer made but then again I could be wrong on the no longer made part. What are the problems it's having other then it is sick? I might be able to help you get to the root of the problem so at least the repair bill will be cheap.
 
Last time I had a problem with one of these, it wound up being either the D/A convertor or the switching setup just ahead of/behind it, I think the D/A. They have the strangest D/A deal I've ever seen. IIRC, and I wasn't quite sure at the time exactly what was going on, they use half the chips they should. They double up the outputs, and data rate, using a diabolical switching setup that struck me as the engineers saying "check this crap out, aren't we the cool kids" rather than being necessary. They switched the output value from every other sample (I think) to the alternate outputs, or somesuch. Somehow, they retained a 20k bandwidth, and a 480 doesn't sound 8 bit, so some juju was uttered to make this all work. I only mention this because you can really get caught up trying to trace down the circuit going WTF! No, it's not a stereo D/A chip. Yes, it's running two channels. No, you're not crazy (well, not because of this, anyway). Yes, it makes me want to damage somebody at Lex too. Knowing this makes it infinitely easier to trace back from the outputs. So check your D/As. PCM 53 or 54 I think, and a cluster of FET(?) switches near them (DIP14 or 16). I want to say DG308 or the ilk, but I might be stuck in V series land.

The other 480 issue I've run into more than once is the little output amp/line driver cards have bypass/coupling(?) caps that fail short (tants, i guess) and drag the beast down. Check your rails. They can usually be seen to be either cracked or seriously discolored with a loupe (ah, surfacemount and aging just don't go together). The little cards themselves are a bear to unsolder without losing any of the legs, which are soldered to both pieces. Solid core Cat5 or busbar can be used to replace any that go astray, but still.
 
would that I had read this before we sent it off to Harman!
I reckon you could be correct Aurt...The -15V rail was being slugged out and I suspected a cap-short but couldn't find it in the time given so away it went... :sad:

chef
 
When these boxes were designed, D-A converters were expensive. Look at the Lexicon PCM60 - the single D-A converter is used for the A-D channel and two D-A channels. The PCM42 works the same way. You do this if a D-A chip costs $50.00, and an analog multiplexor, sample-and-hold, and a bit of software costs you $5.00. It is too easy to look at an old design and shake your head knowing what IC's are available now. I commonly think that when looking at early 1980's console automation systems.

I had the -15 rail go out on a DeltaLabs DL-2 and it was a capacitor in the power supply. Put in a new one, and I know why the old one failed. The capacitor was quite undersized for the current draw of that rail. To me, a ripple voltage of almost two volts is too much.
 

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