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 Forum index » DIY Hardware and Software » The Repair Shop
K2600 (Kurzweil) display and the elastomeric connection
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kkissinger



Joined: Mar 28, 2006
Posts: 1354
Location: Kansas City, Mo USA
Audio files: 42

PostPosted: Tue Nov 11, 2014 8:50 am    Post subject: K2600 (Kurzweil) display and the elastomeric connection
Subject description: Fixed!!!!
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Well, I am writing this post with egg on my face...

I am trying to recover from a botched repair attempt on my Kurzweil's LCD display.

From what I know now, the problem is the power supply (inverter) for the display's backlight however I didn't discover this until I examined my display screen.

The connections from the PCB to the screen are accomplished with an elastomeric connector. To add to the fun, a ribbon cable came loose from the end of the screen -- and it is some kind of heat-applied cable (no solder).

Well, I hope I can put this back together and get it to work. So here are some questions:

1) how do I align the PCB screen with the underlying circuit board? Or, is the alignment that critical?

2) how do I re-attach the ribbon cable to the end of the PCB? I think it may be some kind of heat-sensitive thing -- but not sure on it.

Anyway, if I can "recover" from this error, then I may be able to fix the power supply and be up-and-running again.

I don't think the synth is worth having serviced by a repair shop however my attempts to identify a repair shop for this (relatively old) synth hasn't worked out so well. If I fail on this repair I will probably declare the keyboard as FUBAR and get on with my life.

Any help or advice will be appreciated!

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Last edited by kkissinger on Thu Sep 29, 2016 7:41 pm; edited 1 time in total
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kkissinger



Joined: Mar 28, 2006
Posts: 1354
Location: Kansas City, Mo USA
Audio files: 42

PostPosted: Mon Nov 17, 2014 7:28 am    Post subject: Reply with quote  Mark this post and the followings unread

Hello to all!

Well, I checked with Sweetwater and confirmed that replacement LCD displays are hard to find.

My plan is to attempt a repair -- although I'm not holding out great hope that I will get it working again.

My next plan is to see if I can find another Kurzweil synth (sometimes they are relatively cheap) and see if I can scrounge the parts that I need from it.

Anyway, I will update this thread with information as I move ahead with all of this. Of course, any advice will be appreciated!

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kkissinger



Joined: Mar 28, 2006
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Location: Kansas City, Mo USA
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PostPosted: Thu Jul 16, 2015 2:52 pm    Post subject: Update on my Kurzweil K2600
Subject description: Making progress! Jumping into SMD!
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I've had little time to work with the K2600 (it is currently in pieces) however I managed to find schematics to it!

Turns out that I had to replace two voltage regulators and a capacitor on the power supply board. This brought the backlight and fan back to life.

In addition to my original LCD board, I acquired another one.

However, on one of my attempts to install a new LCD device I had mis-wired the ribbon cable and it looks like I fried the driver chip for the LCD card. (The reason that I think I fried the device is that my oscilloscope shows digital input to the device but no digital output from it. The symptoms are consistent with the data flow as depicted on the schematic.

Well, the chip is inexpensive (i.e., 50 cent) however it is a surface mount device so this provides me the incentive (and excuse) to acquire an SMD rework station. I just ordered an infrared unit and some heat tape (I already have tweezers, etc) and I'm looking forward to making the repair AND setting the stage to do more SMD work in the future.

One of my first DIY SMD projects will be to mount SMD transistor pairs on boards so that I can use them in through-hole circuits. (This part is available as SMD but no longer available as a thru-hole part.)

I have really missed the use my K2600 and hope that I will have some good news to add to this thread soon.

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kkissinger



Joined: Mar 28, 2006
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Location: Kansas City, Mo USA
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PostPosted: Wed Jul 29, 2015 6:13 pm    Post subject: Reply with quote  Mark this post and the followings unread

Just discovered yet another "gotcha" with this repair: the parts list (from the service manual) specified an SOP-20 for the transceiver chip however once I pulled the PCB out I discovered that the SOP-20 is too small! Indeed, the actual part is an SO-20 shape. So.... the project is on hold at the moment while I wait for the correct part to be delivered to me.

This repair job is certainly testing my persistence. Smile

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kkissinger



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Location: Kansas City, Mo USA
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PostPosted: Fri Sep 16, 2016 5:21 am    Post subject: The repair continues Reply with quote  Mark this post and the followings unread

At the electro-music conference, I spoke with Dan Grey (who himself is an expert on digital circuit boards) and he gave me some valuable advice on how I can proceed to troubleshoot and repair my K2600.

He also examined the schematic with me and explained the buss structure and suggested that I acquire a logic analyzer and probes.

Well, I found a 16-bit logic USB logic analyzer on Ebay (not overly-expensive) and I should have it in my hands in a week or so. Also, I found a troubleshooting checklist in the K2600 service manual -- I am not sure why I missed it before -- that suggests what parts I need to check that can cause a blank display screen.

The K2600 is really an awesome machine and I hate to "trash" it for nothing more than a bad display because everything else is working on it.

OK, that's all for now -- I will update this thread whenever I have some kind of "breakthrough". Of course, I appreciate any suggestions!

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kkissinger



Joined: Mar 28, 2006
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Location: Kansas City, Mo USA
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PostPosted: Thu Sep 29, 2016 7:38 pm    Post subject: Fixed!!!! Reply with quote  Mark this post and the followings unread

Though I had replaced the display, the new display was blank.

Well, actually, it wasn't really blank -- rather the PNP transistor for the display's constant current source (on the scanner card) had blown. The solution was simply to replace the transistor.

What was happening was, with the blown transistor, the current was so high that every pixel on the LCD was "on" (even the ones that should have been "off"). The current is set by a contrast control pot. Once I replaced the faulty transistor, the display worked and the contrast control worked.

I was able to make zero progress on all of this until I acquired a complete set of schematics for the K2600. I feel very fortunate that I was able to get them.

Anyway, I am rejoicing today -- I was so afraid that I'd NEVER get this keyboard working again. And to think, the fix was to replace a seventeen-cent transistor.

party time!

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blue hell
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Joined: Apr 03, 2004
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PostPosted: Fri Sep 30, 2016 2:14 am    Post subject: Reply with quote  Mark this post and the followings unread

Great you found that!
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also .. could someone please turn down the thermostat a bit.
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varice



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PostPosted: Fri Sep 30, 2016 3:07 pm    Post subject: Re: Fixed!!!! Reply with quote  Mark this post and the followings unread

kkissinger wrote:
...I was so afraid that I'd NEVER get this keyboard working again. And to think, the fix was to replace a seventeen-cent transistor.

party time!

Congratulations! Good to know that you were successful in making the repair.

kkissinger wrote:
...I was able to make zero progress on all of this until I acquired a complete set of schematics for the K2600. I feel very fortunate that I was able to get them...

Yes, that sure helps. Were you able to get the schematics directly from Kurzweil, or did you have get them from someone else?

Many years ago, I had a serious problem with my Prophet-5. Fortunately, Sequential Circuits offered the service manual including schematics for sale so that I could do my own troubleshooting and repair. I thought at the time that the price was a bit high, but it turned out to be a good investment. More recently, it seems that manufacturers are more reluctant to provide service manuals/schematics. I’ve had to resort to getting them from third parties on the internet (if I could find them).

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kkissinger



Joined: Mar 28, 2006
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PostPosted: Fri Sep 30, 2016 6:00 pm    Post subject: Re: Fixed!!!! Reply with quote  Mark this post and the followings unread

varice wrote:
Were you able to get the schematics directly from Kurzweil, or did you have get them from someone else?


I found them for sale (hard-copy format) from an Ebay seller. It took a while for the K2600 schematics to pop up on my searches.

My thought is that in the future -- before I purchase used equipment -- I will first make sure that I can acquire a service manual and schematics to assure that I can keep the equipment running.

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DES



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PostPosted: Sat Oct 01, 2016 10:37 am    Post subject: Reply with quote  Mark this post and the followings unread

Congratulations! Very Happy
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Danno Gee Ray



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PostPosted: Thu Oct 06, 2016 6:39 pm    Post subject: Reply with quote  Mark this post and the followings unread

Well Done Kevin!

Seems youare more expert than I.
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kkissinger



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PostPosted: Thu Oct 06, 2016 7:43 pm    Post subject: Reply with quote  Mark this post and the followings unread

Danno Gee Ray wrote:
Well Done Kevin!

Seems youare more expert than I.


Thanks Dan. However, you are WAY beyond me with SMD and digital circuits. Thank you so much for your advice that enabled me to replace that tiny, tiny, tiny transistor. Smile

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