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lexicon 224 dead larc Reverb/Delay Processors (HW)
Old 14th May 2018
  #1
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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; 14th May 2018 at 05:53 PM..
Old 14th May 2018
  #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 14th May 2018
  #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 14th May 2018
  #4
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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 14th May 2018
  #5
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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 15th May 2018
  #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 15th May 2018
  #7
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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 16th May 2018
  #8
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Beamish Electronics in Cleveland, OH can probably service it.
Old 16th May 2018
  #9
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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 16th May 2018
  #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 16th May 2018
  #11
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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 17th May 2018
  #12
Gear Nut
 
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 17th May 2018
  #13
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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
Old 31st May 2018
  #14
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hey guys,
i had to take a break from this waiting for some spare parts. and it turns out that the error is power related after all. i did measure the voltages sloppy. only measured for dc which measured fine. but it turns out that all my +v lines show big amounts of ac on them. the ac value is about twice of their dc voltage.

so on my +5v line i measure 10vac, on my +12v line its 24vac etc
my -v lines seem clean - or im too stupid to measure them correctly.

so i double checked all diodes and caps in the psu but they seem fine. i cant measure the huge c1 since my lrc doesnt go up that high. but i put in a brand new one. at this point im not sure, if the error sits within the psu or if it could be a bad voltage filter section on one of the cards as well. anyone know?

im really bad when it comes to basic electronics, but from what i know it sounds like the capacitors after the rectifiers are messing up?

if i dont get any input id get some load resistors in order to run the psu on itself and try to narrow the error down that way. and no worries - im a electronic noob but i know how to properly discharge caps etc... so im not in danger

ps: all ground connections to the psu seem fine.
Old 31st May 2018
  #15
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here is a schematic of the psu. in case anyone has the time....
Attached Files
File Type: pdf 224 psu only.pdf (290.4 KB, 21 views)
Old 31st May 2018
  #16
Usually the large 5 volt computer can cap needs a replacement. Then replace all the other caps on that psu card. I use larger values on the input and output of the regulators.
Old 31st May 2018
  #17
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hey jim,
thanks for the reply. i assume you are talking about the huge c1 capacitor right next to the fan? thats what i would assume too after reading all day about psu and recitifiers.

problem is that i did replace it. but maybe i blew again inbetween workstages....(i did find some burned diodes which i only replaced after inserting it)?
when i received i could hear a rattling sound when shaking it. when i looked at it again today i can shake it as much as i want - it makes no physical sound. i never worked with caps this large so i dont know if this is normal.
my lrc cant measure it since the value is too high 47000uf.

i cant work on it now - i messed up last night. powered it up without the top board inserted and my 5v fuse blew. knock on wood that nothing else happened. but i think it just did not see a load and drew too much current.

now one more idea im having after reading about ripple on wikipedia is a blown voltage regulator u1. according to wikipedia voltage regulators are sometimes used to supress ripple. on the attached schematic there is ac all over the place surrounding it - so it might be normal up to that point? i need to learn more about psus.... im at it but very happy for any further help obviously. thanks!

ps: the one thing im scratching my head about is that this happens on all lines. say c1 was blown - would that not only cause ac on my +5v line? its on all lines +dc lines.
Old 31st May 2018
  #18
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i also measured all cables coming from and to the psu boards for continuity. all contacts are solid.

i need to find out if this is a certain psu error, or if one of the cards could cause this too. after burning the fuse im too scared to take out any of the boards while powering up though. so unless one of you can tell me, i think i have to go get some load resistors and run the psu by itself.


and another noob idea: say my main 115/230 switches are oxidated and wrongly set to 115v. maybe the psu can take it but its filter caps are now the wrong value? im a noob

also all seals on the trim pots have their factory seal broken. so they might be set wrongly.

Last edited by salomonander; 31st May 2018 at 06:27 PM..
Old 4th June 2018
  #19
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crosscutred's Avatar
You should be ok disconnecting the power supply from the rest of the circuit without using a load. You may be thinking of speakers and amps.

Without a load you won't be able to verify if it isn't able to supply the current you need (amps) but you should be able to measure the voltage it produces and find the AC without risk to itself ..... infact if you leave it connected you risk damaging other parts of the circuit.

Internal power supply's often have a connector to simply unplug and that isolates the psu from the rest of the circuit. Which is also a good place to start taking measurements.
Old 5th June 2018
  #20
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thanks mate,
i think you are wrong here... or my unit is really f*cked
i ran it without the top card installed and killed my 5v line. im still waiting for a replacement 2n5885 transistor to fix it (it burned out).

thats why i did not post. im waiting :( but inbetween i did find another capacitor that had the wrong value and three wrong jumpers on the main board. im starting to really get to know this unit

im also not certain about the bunch of jumpers surrounding u16 on the top board. my schematic is unreadable and from the photos i see on the net their jumpers are configured differently. but i dont know what that jumper does. it might be there for the expansion card. if anyone knows, please let me know. i attached the unreadable schematic. maybe someone else can read it.....
its on page 102 of the service manual.
Old 5th June 2018
  #21
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here are the jumpers
Attached Thumbnails
lexicon 224 dead larc-jumper-lex.jpg  
Old 5th June 2018
  #22
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ps: the tech before me recapped everything with panasonic ga caps. does anyone know if these even qualify as a tantalum replacement. i cant find any esr ratings.
Old 5th June 2018
  #23
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crosscutred's Avatar
Quote:
Originally Posted by salomonander View Post
thanks mate,
i think you are wrong here... or my unit is really f*cked
i ran it without the top card installed and killed my 5v line. im still waiting for a replacement 2n5885 transistor to fix it (it burned out).
So other cards were still installed and connected? Is it possible they were the cause of the 5v line going down?

I suppose that leads to the question,
how are you going to identify if the fault is in the power supply or on the cards?

I've never damaged a power supply by not having it plugged into the thing it is supposed to power, I have had power supplies fail when not plugged into their load but it's rare and always a problem with the supply.

It is possible the power supply needs the other components to switch on (like a computer power supply) or that there is a short somewhere caused by the removal of other parts but the design of all electronics I have encountered allows for the isolation of the power supply from what it is powering for trouble shooting.

Your 5v failure may be that the board you removed caused a short in the process of removing it or that it was failing in a way that prevented the short being in the circuit, removing the board could have removed the protection circuit from the system. There are a few possibilities but the likelihood that the supply will be damaged by running disconnected is extremely remote.

I hasten to add I have never worked on one of these units so if anyone knows otherwise then put me right.

The first steps I would always take when working on faulty electronic equipment is to isolate the power supply and measure if it is supplying the correct voltages. I recommend you start there.

Good luck.
Old 5th June 2018
  #24
Quote:
Originally Posted by salomonander View Post
ps: the tech before me recapped everything with panasonic ga caps. does anyone know if these even qualify as a tantalum replacement. i cant find any esr ratings.
The FM and FR are their low impedance caps.
Old 5th June 2018
  #25
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Quote:
Originally Posted by Jim Williams View Post
The FM and FR are their low impedance caps.
im aware of that thanks. the ga is what is in there. im wondering if they may cause issues.

ps: my hopes are up pretty high at this point. still waiting for the parts to fix my 5v rail, but after checking all the work the techs before me did i found lots and lots of wrong jumpers on the main processor board. one reversed cap on the 5v rail on the main board and one 1uf cap that is supposed to be 10uf. edit: looks like the guy used dice to set his jumpers...
im fixing all this right now. its really hard to read the service manual that is online via google. and one board is missing completely from the schematics.

does anyone have a different version of the service manual than the one from google 1st hit?

Last edited by salomonander; 5th June 2018 at 07:55 PM..
Old 5th June 2018
  #26
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I really need a schematic for the logic processor that is revision G.

and i need a a schematic of the DAC that is revision 2

if anyone can help ill happily pay you for scanning these documents for me.
Old 6th June 2018
  #27
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Bingo!
photos are good enough to make out jumper positions

https://www.ebay.ph/itm/USED-NATIONA...1/351242724991
Old 6th June 2018
  #28
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Quote:
Originally Posted by salomonander View Post
im aware of that thanks. the ga is what is in there. im wondering if they may cause issues.
to answer my own question: yes they might do. they have bad esr readings and i just recapped the whole unit with panasonic fr and tantalums. nothing else i can do while waiting for a darn 2n5885 power transistor....

if anyone stumbles across this thread down the line you can find more schematics here:

ftp://ftp.hmgsl.com/LEXICON/Legacy/
User: customer
Pass: service

its a mess. and half of the 224 docs are actually in the 224x service manual for some reason. but there is some more info.
Old 7th June 2018
  #29
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received a pm from a very friendly fellow slut who had the same issue. it was fixed by making sure that all caps had a proper contact to the top pcb. the big caps expecially. i might have had a bad connection to the big 45000uf cap on the top trace since the pad its screwed on to was rather oxidated. i cleaned it and made sure i have a solid contact. Still waiting for my 2n5885 but i should know more tomorrow. Thanks Stefan!
Old 8th June 2018
  #30
Gear Nut
 
rtype909's Avatar
hi,
from what you say there is probably a short somewhere on the 5v rail. you need to work out where that is - it could be on any of the boards
Also ensure the earth is still connected on your 224. I did buy a 224 from the USA to fix and a tech had cut the earth.
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