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Lexicon PCM 70
Old 14th October 2013
  #1
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VintageAnalogue's Avatar
 

Lexicon PCM 70

Hi

I have been given a non-working Lexicon PCM-70 and I would like to attempt replacement of the electrolytic caps. I am used to working on tube gear and discrete circuits/early solid state gear but less savvy with later stuff. Can anyone tell me whether the pcb in the Lexicon is multilayer/double sided? I am worried about lifting the copper cores that go through the board if they exist on the Lexicon pcb. If there aren't any then I'm good to go.

Best

Dave
Old 15th October 2013
  #2
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Download the Service manual, also remember there are 3 revisions of the PCB Board as well as software from 1.x, 1.2, 2x, 3.x, and yes, you can take the PCB board out of the unit, just be careful when unplugging the ribbon to the front panel display. Apart from that, its not clear what your problem is.....just what you have experience doing and don't!
More info on what the PCM-70 is doing would help many offer an experience, I'd reseat the eproms before anything as electromagnetic interference can make those units go down!
Old 18th October 2013
  #3
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VintageAnalogue's Avatar
 

Thankyou for your reply.

The Lexicon, when powered up has no display and only allows sound through it on bypass. The bypassed sound is affected by the input gain knob and the coloured level indicators work. Other than that, nitto.

I have downloaded the schematic for the Lexicon.

I am no electronic engineer but am okay with tracing problems on tube and vintage solid state gear. As the majority of this Lexicon is not working, I am assuming a pretty global problem such as power supply. My main concern is damaging the board when removing the capacitors as they have the "via" through the board to link the two circuits.

I will take your advice and try reseating the eproms tomorrow before going any further. I have a static wristband to protect the circuits from static. I have just used the reseating trick to get a monosynth going.

This particular PCM70 came from the estate of Keith Grant (Olympic Studios) and was in his Creek Studio when he passed away. My friend bought a job lot of gear from the studio and this was amongst it. He gave it to me as it was dead and because he knew I like fixing things.

Rather than risk damaging it, if the reseating of eproms and replacing of electrolytics doesn't cure the problem, I will take it to a pro for repair.

Thanks again for your help and advice.

Dave
Old 19th October 2013
  #4
Gear Maniac
 

I have a PCM70 that will only increment in values. Any fix for that?
Old 19th October 2013
  #5
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Quote:
Originally Posted by VintageAnalogue View Post
Thankyou for your reply.

The Lexicon, when powered up has no display and only allows sound through it on bypass. The bypassed sound is affected by the input gain knob and the coloured level indicators work. Other than that, nitto. I have downloaded the schematic for the Lexicon.

I am no electronic engineer but am okay with tracing problems on tube and vintage solid state gear. As the majority of this Lexicon is not working, I am assuming a pretty global problem such as power supply. My main concern is damaging the board when removing the capacitors as they have the "via" through the board to link the two circuits. I will take your advice and try reseating the eproms tomorrow before going any further. I have a static wristband to protect the circuits from static. I have just used the reseating trick to get a monosynth going.

This particular PCM70 came from the estate of Keith Grant (Olympic Studios) and was in his Creek Studio when he passed away. My friend bought a job lot of gear from the studio and this was amongst it. He gave it to me as it was dead and because he knew I like fixing things.Rather than risk damaging it, if the reseating of eproms and replacing of electrolytics doesn't cure the problem, I will take it to a pro for repair. Thanks again for your help and advice.
Dave
No problem, PM me if you want the full service manual, you might want to try Beamish Electronic's in Chicago or Benden Tech in the UK, if some of the IC And Ram plus Lexichip's and ARU are not socketed you might have an very early 1.2x version unit, these suck EM interference badly and are actually susceptible to short just by inputting the wrong current into a Send/Return Input/output etc. If the unit powers up, half the battle is over, I would try a total Upgrade on all Sockets and get version 3.x software with a New O.S (Gal Chip 28 pin) for 30$ Bucks on evil-bay before anything. PM me if you know the specific faults and I'll try to walk you through some fixes. Or Google PCM-70 fixes or search here on GS, many units have been saved by the collective brain on GS. I can certainly see you wanting save a "Mojo Olympic Studio Unit" etc...! I would want the same unit working after so many recording's!

Quote:
I have a PCM70 that will only increment in values. Any fix for that?
Sounds like you have a front panel button that has gone rogue, the best thing to do, is not touch it if all else is working and if it's really bugging you that you can't program the unit. Use Soundiver Software via System Ex and Midi to Program the PCM-70 then save and reset Algo's and presets easily! Unless you want to go down the rabbit hole of taking the unit & front panel apart to fix 1 button an/or reseat it; I.E this would be an easy optional route to a full hardware fix! Google and search GS as well! Cheap & easy no big money fix (You can also restructure your Presets so you cycle from 1-50 in your preferred order when required to mix etc, though again 3.x software on the PCM-70 controls Dynamic Midi the best! V.2x is nice, though the full midi spec not 100% compatible (Maybe that should read reliable as the 2.x system ex bursts can take time!).

Cheers & Good luck!
TLB
Old 20th October 2013
  #6
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VintageAnalogue's Avatar
 

Quote:
Originally Posted by TheLastByte View Post
No problem, PM me if you want the full service manual, you might want to try Beamish Electronic's in Chicago or Benden Tech in the UK, if some of the IC And Ram plus Lexichip's and ARU are not socketed you might have an very early 1.2x version unit, these suck EM interference badly and are actually susceptible to short just by inputting the wrong current into a Send/Return Input/output etc. If the unit powers up, half the battle is over, I would try a total Upgrade on all Sockets and get version 3.x software with a New O.S (Gal Chip 28 pin) for 30$ Bucks on evil-bay before anything. PM me if you know the specific faults and I'll try to walk you through some fixes. Or Google PCM-70 fixes or search here on GS, many units have been saved by the collective brain on GS. I can certainly see you wanting save a "Mojo Olympic Studio Unit" etc...! I would want the same unit working after so many recording's!

Cheers & Good luck!
TLB
Thanks for your comprehensive answer TLB. At the moment the unit appears dead although the only thing on the front panel working is the led meter and the input gain control. The gain button on the rear panel also works.

I have reseated all of the chips that are in sockets. When I connect the unit up to a bus on my mixer I can feed signal through which comes out dry. The level is affected by the input gain level and the gain button on the rear. The input led level lights work in relation to the input signal.

As the e-caps are 27 years old I'd like to change them in the power supply but I cannot find replacement caps for C143 and C153 that are 25mm in height and 30mm in diameter. Is it possible to use a smaller leaded radial cap of the same values and specs rather than the current "snap in" type ?

I agree that I should go through upgrading chips once I "get the lights on".

The board spec says that it is a 1986 Rev. 4. Keith had type three os chips in there.

I'm in the UK ad have seen Benden's page. My friend had some success with him so if I cannot do this myself I will enlist his services.

Best

Dave
Old 20th October 2013
  #7
Gear Head
 

TLB!
Thanks for the info on the PCM 70!! I have an older unit that seems to work and then turn off by itself. I'm pretty sure it's a voltage regulator issue as I have measured the 5v and that goes when the unit shuts off. Last time I looked the voltage regulator was impossible to find. Some special chip. Do you have any insight that might point me in the right direction to get it working?
Thanks so much for taking the time!
Mike
Old 20th October 2013
  #8
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VintageAnalogue's Avatar
 

Quote:
Originally Posted by mhartung View Post
TLB!
Thanks for the info on the PCM 70!! I have an older unit that seems to work and then turn off by itself. I'm pretty sure it's a voltage regulator issue as I have measured the 5v and that goes when the unit shuts off. Last time I looked the voltage regulator was impossible to find. Some special chip. Do you have any insight that might point me in the right direction to get it working?
Thanks so much for taking the time!
Mike
You could always start your own thread
Old 21st October 2013
  #9
Lives for gear
 

Quote:
You could always start your own thread
Nope....It's all OK, I shall endeavour to point you in the right direction! Share the Knowledge as a collective has always been my vibe on such matters! Everyone should come out with a working PCM-70! Unless a fatal Component has gone, then it's a case of finding a Dead unit and doing a swift swap out!


Quote:
Originally Posted by mhartung View Post
TLB!
Thanks for the info on the PCM 70!! I have an older unit that seems to work and then turn off by itself. I'm pretty sure it's a voltage regulator issue as I have measured the 5v and that goes when the unit shuts off. Last time I looked the voltage regulator was impossible to find. Some special chip. Do you have any insight that might point me in the right direction to get it working?
Thanks so much for taking the time!
Mike
Sounds like your actual Power supply is certainly not managing the correct voltage on both rails, the PCM-60 and PCM-70 do actually share the same Power Supply, and a Clacking or Clicking of the Power Supply continually is showing that the Power Supply relay is wanting to shutdown as the unit's logic is simply not seeing enough full power after the PCM-70 Power Up Routine. This 100% indicates the unit is certainly not receiving the power after the initial current "IN-RUSH" stage requires. I suggest you check your settings on the back as you want 110/220/240V Fuse (Often Internal on most PCM-70's & 60's) though you might have also blown the "FUSE" in the units Power supply....So yes, being 5volts down on a rail would indicate that you are correct.

I'm afraid you will need to unplug the unit of ALL CONNECTIONS and that Includes IEC POWER CORD, then your going to have to take off the lid, and make sure that your "Fuse" is the correct type required for the PCM-70. Please download the PCM-70 service manual or PM me an actual IP Address (No Google, Yahoo or MSN etc And I will send it along) and you will see that the Power supply is at the back of the unit facing you with display (Front On) in the right hand back of unit position. Inside you will find the PSU itself, and a junction for changing the voltage from 110/220/240 then get the correct Power Position for your country and a new Slow-Blow fuse and see if that makes a difference. The pin out for changing the Power supply from 220 to 110 Volts is a simple affair. Please DO NOT HAVE THE UNIT PLUGGED IN WHEN DOING THIS.

If you are using a Step up/Down Transformer instead of changing the units power..... the clacking would indicate that the Step up/Down Trafo is not supplying enough current. Simple as that. As Posted By Mr. Vintage Analogue please also look at all caps and change (Please also discharge your Eproms - I.E Unplug them all, discharge them, then reseat them. Simple as that.) while you have the unit open. Place the unit on an Antistatic Mat with Wristband and yourself grounded as I've written PCM-70's loathe EM fields and can be eaten by them very easily. The Voltage regulator is around the small daughter card near the PSU in the PCM-70. Sorry, I can't draw the design here though I might put up a PDF. Let me check! Please remember VOLTAGE is DANGEROUS and can Kill you. If you don not feel confident taking on the Power Supply in the unit, please pay the extra $50.00 Bucks for a Tech to do the change over in 15 minutes.

Please see the Service manual Pin out I have included here and also see the next Post:
TLB

https://www.gearslutz.com/board/attac...1&d=1382328067
Attached Thumbnails
Lexicon PCM 70-pcm-70-voltage-100-240v-pin-out-fuse.jpg  
Old 21st October 2013
  #10
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Lexicon pcm-70 service manual for diagnostics

Quote:
Originally Posted by VintageAnalogue View Post
Thanks for your comprehensive answer TLB. At the moment the unit appears dead although the only thing on the front panel working is the led meter and the input gain control. The gain button on the rear panel also works.
This I feel is a good sign as obviously the ADC is working, and the Gain elements and PSU are operational - Relays etc and Levels working are a great sign, loose connections are where I would be looking now as you say your attempting to do!

Quote:
Originally Posted by VintageAnalogue View Post
I have reseated all of the chips that are in sockets. When I connect the unit up to a bus on my mixer I can feed signal through which comes out dry. The level is affected by the input gain level and the gain button on the rear. The input led level lights work in relation to the input signal. As the e-caps are 27 years old I'd like to change them in the power supply but I cannot find replacement caps for C143 and C153 that are 25mm in height and 30mm in diameter. Is it possible to use a smaller leaded radial cap of the same values and specs rather than the current "snap in" type ? I agree that I should go through upgrading chips once I "get the lights on". The board spec says that it is a 1986 Rev. 4. Keith had type three os chips in there.I'm in the UK and have seen Benden's page. My friend had some success with him so if I cannot do this myself I will enlist his services.
Best
Dave
I'm thinking your looking at the problem in the right way, you need to look at the Battery as well as the VDU display and that all Connections are tight to functioning level, once you've achieved this and replaced the older Caps you feel have seen their day - trace the diagnostics from the schematics & service manual. Dave, As your problems seem a touch more serious then above and you have the Schematics, I'm going to throw in the service manual here as changing Caps means your going to have to find tolerances as close as possible to the original parts, and these can be found often with a +/- 3/% (Often 5%) differential. Even if the Murata Filter has gone, it can be replaced with a 4 pole butterworth design that has been created for these specific purposes. Dave, you will also going to need the service manual, and check your traces as you move along making sure each part is receiving what the unit requires.

As you've done plenty of Analogue type stuff I doubt that you will find it too hard in using a scope to make sure your tolerances and subsequent materials for swap outs are compatible, you also seem to have a PCB Marked V.4 this from 1986 would indicate to me it is indeed a PCM-60 board rebranded for PCM-70 use (This was quite common by Lexicon during the day of production as the PCM-60 and 70 live only some 14 months apart in OEM Birth). Dave, you seem quite proficient in tracing certain faults and problems though possibly a touch worried you could ruin the PCB by punching through it by unsoldering various components. I would take the back of the PCB Board and Photograph each Trace in 1/4's (Say w/ an iPad/Camera etc) before attempting to unsolder from the back as well as Top side PCB. Should you require certain parts I might be able to help, and "Like for Like" (At it's closest Lexicon tolerances in parts in early units were not very tight) is usually not a problem though as your aware of Benden Tech can help you deal with this re: advice. I will also dig out some ECO's for you to make sure your parts requirements have no repercussion's......Just in case as PCB revisions were often amended w/ Fixes.

Though do keep in mind that the PCM-70 is a PCM-60 though with better Logic, Ram, and Algo Control. I'm pretty sure your 99% capable of doing this work in your own time when required - Again, as I say to Everyone - Please make sure No Plugs or IEC cables are plugged in and the Power is Off! Hopefully the service manual will fit in this post. If the PCM-70 Service Manual does Not load here..... Please PM me and I shall E-mail it to you! You require this document to reset your PCM-70 correctly. Dave, you can also upgrade the ram (SRAM) to 512K, this will not operationally make the unit's delay times longer, though the NS speed of Ram & and larger sized chip will make the PCM-70 handle tasks in work such as access burst & control logic involving Midi and or Algo Operational speed faster by 15-20%, thus a System Ex Midi unit with upgraded SDRAM is faster in buffer speed etc & understood to react much more quickly. Some people notice a difference, others say it doesn't matter - just a thought while uploading this PCM-70 Service Packet for the PCM-70 !

Regards
TheLastByte

https://www.gearslutz.com/board/attac...1&d=1382331061
Attached Files
File Type: pdf PCM70 Service Manual.pdf (7.15 MB, 680 views)
Old 21st October 2013
  #11
Gear Maniac
 

Quote:
Originally Posted by TheLastByte View Post

Sounds like you have a front panel button that has gone rogue, the best thing to do, is not touch it if all else is working and if it's really bugging you that you can't program the unit. Use Soundiver Software via System Ex and Midi to Program the PCM-70 then save and reset Algo's and presets easily!
Thanks for the reply. I didn't even know Soundiver was still around. I used it around 20 years ago for my E4X. If I remember, it was Mac only, and I'm not using a Mac anymore. I could probably set up a substitute for Windows.

Mike McRoberts
Old 22nd October 2013
  #12
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Quote:
Originally Posted by mcmike View Post
Thanks for the reply. I didn't even know Soundiver was still around. I used it around 20 years ago for my E4X. If I remember, it was Mac only, and I'm not using a Mac anymore. I could probably set up a substitute for Windows.

Mike McRoberts
Hi Mike,
Your spot on Man, these are quite old programs I.E.... Unisynth (Motu) and Soundiver (Logic 8 was it's last run from memory?) plus I'm sure there are a few other of these style Midi Control Programmable Software packs that do still work under OS X 10.6 Snow Leopard 32 bit or Windows and thus will be able to program the Lexicon PCM-70 from a Midi Source in your Computer. A trip into Google should see you hooked up to the right program! All you need for a Mac/PC is then a System Ex Librarian & Midi connection etc, and these small programs are Free/Shareware and come in hundreds of guises! Yeah...(Big Sigh), I still keep a Rack of EMU samplers, & couldn't think of tossing them out....Lol! The Emulator E4 Platinum w/ "128 Megabytes".....Yeap..128 Megabytes and all options Inc AES & Adat, 64 midi In/Out was near $8000 bucks, though were also fully fledged Synths not just Samplers (Which was the difference Vs Akai IMHO...!)

The point? Really unless a PCM-70 with a busted button is driving you insane and you want to spend time getting the hardware fixed by a tech or yourself, doing the Algo programming via System Ex is just a simple & elegant solution stopping you from messing around the front panel & forking out cash when not required! There are a few programs written for the Eventide H3000 though none where comprehensively written to 100% cover the whole unit, though you can get 90% their if required.

Good Luck!
- TLB -
Old 5th March 2015
  #13
Gear Head
 
drago's Avatar
Hello!

I have a similar problem.

My unit turns on and the audio goes through the entire circuit, but the front panel does not work, the input LEDs work, but the alphanumeric keypad and buttons bypass reg, load, etc do not work.

Someone knows what could happen?

Best!!
Old 9th March 2015
  #14
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Quote:
Originally Posted by drago View Post
Hello!

I have a similar problem.

My unit turns on and the audio goes through the entire circuit, but the front panel does not work, the input LEDs work, but the alphanumeric keypad and buttons bypass reg, load, etc do not work.

Someone knows what could happen?

Best!!
Pull out the EPROM's and make sure you use an Anti-Static Wristband and Pad, them rest them (Ground them) on Anti Static Foam. Ground the PCM-70 and re-Insert EPROM's and see how your PCM-70 is going then. If you can film/capture this with an iPhone/pod/pad etc the better.

Cheers
TLB
Old 4th November 2015
  #15
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Hi all,
for some reason I am now unable to set the memory protection off on my pcm 70 (ver. 2.0), so I am unable to store edited presets anymore on free register slots.
I do follow the procedure described in the manual: I load program 7.0, then select parameter 0.1, then use the rotary knob to select memory protection off. Fact is, when I turn the knob, I get this enigmatic "m protect m (space) e" message. I cannot switch from on to off.
Anyone?
Thank you very much for your help

best regards
Massimo
Old 7th January 2016
  #16
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Hi, I have a similar problem.
I hope this Lexicon PCM Manual can help you.
Old 7th January 2016
  #17
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massimo's Avatar
 

Yes, I did solve the problem by doing the reset (the more radical option, which deletes the user presets) following the manual. While I had experienced the scrambled fonts on the display issue before, and had promptly attributed this to the tension spike as suggested by the manual (and solved this with the less radical reset option), in the case I was describing in my original post the issue presented itself differently and was therefore disconcerting. I am happy to report that this is also solved through a reset.

Best Regards
Massimo
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