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lexicon 224 dead larc Reverb/Delay Processors (HW)
Old 1 week ago
  #1
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Thread Starter
lexicon 224 dead larc

hey,
i have a broken lexicon 224 here that im stuck with. i was never able to use it - i bought it broken for a steal.
problem is the larc. its dead. no lights - nothing. i have checked for continouity from the board to the remote and its all fine. the cable extension within the remote is fine too. it gets the 10v ac and the 5v rail seems to work fine too. all test points that are stated in the service manual measure the correct voltage as well.....

any suggestions? im kind of lost without any error messages..... i get no error leds from the main unit either.

thanks a lot

ps: anyone know if the larcs of 224, 224x and 224xl are interchangable?

Last edited by salomonander; 1 week ago at 05:53 PM..
Old 1 week ago
  #2
Not interchangeable at all. They each have a different control card mounted. Check to see which your frame has mounted and then try the correct remote, if you can find one. The 224X and XL used the LARC. The others used a different remote.
Old 1 week ago
  #3
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Without a schematic all you have is experience to rely on and with an old piece of digital gear like that it doesn't take long to run into dead ends when you get past some superficial basics.

If an when you do find a schematic its just as much about ruling out what's working as what's not working.
You'll find with allot of digital gear it has to boot to an on condition. It wont begin that process if the voltages aren't right so that's step one.
Allot of old units used batteries to backup the memory so that would be on the top of the list. The batteries corrode and short and therefore no 3~5V DC

If the voltages are right it wont boot unless all signals are correct. Something involved from power up like that battery or a fan or any number of items which boot first aren't working.

After voltages and conditions are good then it would load any kind of information from memory. If a battery has been dead long enough that information may be lost too. Its not like these things had hard drives. They may have had instructions written to a ROM or RAM. If the info was wiped by battery problems good luck on reprogramming. Old chips were often put in a burner to write information. Doubt you'd find many working at Lexicon who would even be willing to do that if they in fact had the gear and knew how.

It can also be chip damage, or just about any electronic component giving you a problem. Again, you'd need a schematic and know how to use a scope and logic problem to even begin to narrow things down. Personally I'd say you got burned and leave it at that. When you buy used gear next time stay away from non functioning digital gear. Repairing it can be extremely complex for even you higher skilled techs. I wouldn't touch anything by lexicon from back then.

The most I messed with was one of their old Harmonizers and got lucky. The problems with it were superficial connector problems. If the thing actually had a bad chip there's no way I could have gotten that thing fixed. Lexicon was factory only repair even back in the 80's. Even if you knew what chip was bad Lexicon wouldn't sell them too you. No doubt its the same with your unit. Granted 30 years may be long enough to where some generic parts have been made available but the odds you'll luck out aren't even in the single digit percentages on a rare unit like this. You may get lucky and it wind up being a simple power or battery issue. Beyond that I'd say sell it for parts to someone else trying to repair theirs.
Old 1 week ago
  #4
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Thread Starter
thanks for the reply. the schematic is the first google entry... so thats not the problem. i fixed a pcm70 once so i do not feel at all like giving up yet - i just started

my unit is a real early one and does not use batteries. so i can rule that out. guess i will have to study the remotes schematic some more.

say there are problems booting up in the main frame - would the remote not give a sign of life? like a led lighting up or an error message on the display? it looks to me like the remote is completely dead. the ics feel warm but thats about it.

any help is really welcome. thanks
Old 1 week ago
  #5
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Thread Starter
one more thing im wondering. someone recapped this before me. he used panasonic fc caps which should be fine as a tantalum replacement. but he replaced the axial caps on the microcomputer pcb with standard axial elkos.
i can only look at pics on the net, but could it be that these were actually axial tantalum caps? cheers
Old 1 week ago
  #6
I used Panasonic FM caps in mine. Lower impedance than a tantalum cap. Usually dirt is the issue with those. Clean every connector, clean the card cage. Oh, get the service manual or leave it alone, you won't help it without one.

H01 error codes are not listed in the manual. They are main frame failure codes from the card cage not connecting to the pcb's.
Old 1 week ago
  #7
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Thread Starter
thanks jim,
i will clean some more. first thing i need to do is to get the larc to show me anything... maybe its the cable after all. it came with two cables. one had pin 1 and 13 broken. so i used the other one - looks to be some improvised test cable from the tech before me. it measures fine for continuity but its a 100 meter (!) long cable. maybe some of the data gets lost. ill report back once i made progress.
Old 1 week ago
  #8
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Beamish Electronics in Cleveland, OH can probably service it.
Old 1 week ago
  #9
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Thread Starter
Quote:
Originally Posted by David Kulka View Post
Beamish Electronics in Cleveland, OH can probably service it.
thanks David,
im in the eu... so shipping would be too much i guess. im just wiring up a new remote cable. maybe it helps. do you maybe know about the max length allowed? i was going for 10 meters - if thats fine
Old 1 week ago
  #10
The LARC uses a standard DB9 connector. Any PC cable can be used to check that. Card cages are cleaned here with a non-residue electronic contact cleaner and a bunch of packing cardboard cut into 8"x2" strips. Soak the ends and work them in and out of the connector slots. See all that crud? That's why it won't communicate.
Old 1 week ago
  #11
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Thread Starter
Quote:
Originally Posted by Jim Williams View Post
The LARC uses a standard DB9 connector. Any PC cable can be used to check that. Card cages are cleaned here with a non-residue electronic contact cleaner and a bunch of packing cardboard cut into 8"x2" strips. Soak the ends and work them in and out of the connector slots. See all that crud? That's why it won't communicate.
thanks Jim,
ill do the edge connectors tomorrow. btw my larc is the old beige one. it uses a db25 connector. within the larc there were also some internal flat cables made from paper that i replaced today. one trace was almost gone. im too tired to fire it up now. will do so tomorrow and report back. thanks for all the help. i really appreciate it.
Old 1 week ago
  #12
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rtype909's Avatar
Quickest way to fix a 224 is to have another working unit so you can flip the cards and identify the problem. It took me 6 months to fix my 224 but only a month to revive another. All components are off-the shelf and obtainable.

Error codes, as has been stated above, do not reveal all problems.

Typically battery leak from the option board, spreads diffusively and damages components and causes all kinds of weird errors - misreporting of errors on DMEM T&C etc. The option board, sockets and potentially chips all need cleaning or replacing.

I would carefully check the DB25 connector if you are getting volts there, change the cable too if you have a straight through DB25 lying around try that.

In the UK you can try Benden Technology - Home

I would go to a tech who has a working 224.
Old 1 week ago
  #13
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Thread Starter
Quote:
Originally Posted by rtype909 View Post
Quickest way to fix a 224 is to have another working unit so you can flip the cards and identify the problem. It took me 6 months to fix my 224 but only a month to revive another. All components are off-the shelf and obtainable.

Error codes, as has been stated above, do not reveal all problems.

Typically battery leak from the option board, spreads diffusively and damages components and causes all kinds of weird errors - misreporting of errors on DMEM T&C etc. The option board, sockets and potentially chips all need cleaning or replacing.

I would carefully check the DB25 connector if you are getting volts there, change the cable too if you have a straight through DB25 lying around try that.

In the UK you can try Benden Technology - Home

I would go to a tech who has a working 224.
cheers,
ill try my new cables today. if that wont help you are probably right. it took me ages once to fix a pcm70 - it was a pain.... i did find a studio in town that has a working 224. i dont know them but will give them a call.... maybe they are nice and willing to rent it out for a few days. best
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