Vintage Synth Repair

Update. After leaving the DX7 getting dust on a shelf for months (leaving my workbench for other synths to fix), I finally found the issue; the 10/16 tantalum close to the battery was open. Once replaced, boots up fine. Tantalums are really the plague of old synths...

--- In vintagesynthrepair@yahoogroups.com, "GB" <grantbt@...> wrote:
>
> Maybe try a few reset chips instead of the cap. You can get them in TO-92 transistor packages and DIP too.
> 
>   ----- Original Message ----- 
>   From: alesisfusion8hd 
>   To: vintagesynthrepair@yahoogroups.com 
>   Sent: Sunday, March 11, 2012 9:57 PM
>   Subject: [vintagesynthrepair] Re: Looking for DX7 service manual
> 
> 
>     
>   Hi Narfman,
> 
>   no the 6805 doesn't get warn.
>   I plugged another 10uF in parallel (giving 20uF), but no change.
>   I tried with another power supply (and another keyboard); still the same.
> 
>   What buzzes me is /RES seems to reach +5V in 10ms; the datasheet says it should stay low for 100ms. That's why my manual reset works.
> 
>   Strange thing: I wanted to sinc my one-trace small scope to the +5V (to precisely measure the time between power on and RES). I made a small BNC cable (coming from an old network cable), but the cable had a short I was not aware of. I took my supply from CN6 (pin 1=+5V, pin 4=GND). When I plugged it to my working DX7, I had the exact same behaviour.
> 
>   --- In vintagesynthrepair@yahoogroups.com, "narfman96" <narfman96@> wrote:
>   >
>   > Good troubleshooting! Does the 6805 get warm? Since all the resets come from the same timing cap you could try a 22uf and see if the extra settling time helps. I found the 6805 on Ebay. Not sure if it's the same package... 
>   > 
>   > --- In vintagesynthrepair@yahoogroups.com, "alesisfusion8hd" <babouche369@> wrote:
>   > >
>   > > Just a follow up. I nailed down my issue to the Sub-CPU 6805 (IC 13) which sometimes does not boot up the right way. When I reset it by grounding pin 28, everything runs smoothly.
>   > > My guess is the condition on power up does not reset the sub-CPU long enough (the 63B03 boots every time; less sensitive? ). That's the best case. The worst case is a defective 6805.
>   > > I changed the 10 uF cap of the Initial Clear, but no success. I'll take a chance and change the 4700 uF on the PSU, or simply switch it with my other DX7.
>   > > 
>   > > --- In vintagesynthrepair@yahoogroups.com, "alesisfusion8hd" <babouche369@> wrote:
>   > > >
>   > > > Thanks man, the tuning procedure is exactly what I was missing. 
>   > > > 
>   > > > I've cleaned up all the connectors (on main board and sub boards); it didn't solve my issue, but it's a good start. I've also tipped on all chips & components to track any dry joint (I'd this issue on a Kurzweil 1000).
>   > > > The issue really resides in the digital part during the init phase. Happily, I've got another DX7, in working condition; I can make some comparisons.
>   > > > 
>   > > > 
>   > > > --- In vintagesynthrepair@yahoogroups.com, "z3sound" <z3sound@> wrote:
>   > > > >
>   > > > > 
>   > > > > hi 
>   > > > > there was no complete Service manual for DX7 (first edition)
>   > > > > on the internet.but now it is 
>   > > > > i just upload the complete DX-7 first service manual in Files
>   > > > > hope it will help......
>   > > > > 
>   > > > > --- In vintagesynthrepair@yahoogroups.com, Kashayar Dashtdar <vdashtdar@> wrote:
>   > > > > >
>   > > > > > Hi my friend.
>   > > > > > 
>   > > > > > Unfortunately there is no complete Service manual for DX7 (first edition)
>   > > > > > on the internet.
>   > > > > > 
>   > > > > > Try these :
>   > > > > > 
>   > > > > > 1- Replace all the electrolytic capacitors in the power supply board.
>   > > > > > 2- Send a fresh sound bank from the PC to the keyboard using a midi
>   > > > > > interface.
>   > > > > > 
>   > > > > > I hope it will make your dx7 work properly.
>   > > > > > 
>   > > > > > Good luck.
>   > > > > > Ciro
>   > > > > > 
>   > > > > > On Tue, Mar 6, 2012 at 8:49 AM, alesisfusion8hd <babouche369@>wrote:
>   > > > > > 
>   > > > > > > **
>   > > > > > >
>   > > > > > >
>   > > > > > > Hi group,
>   > > > > > >
>   > > > > > > I recently bought a first generation DX7 for $ 50. Problem on startup:
>   > > > > > > sometimes starts up OK, sometimes keeps looping, sometimes seems OK but
>   > > > > > > actually frozen.
>   > > > > > > When it starts up OK, I found only garbage in the internal memory, but it
>   > > > > > > works with the cartridge. It does not memorize my settings, and main output
>   > > > > > > seems dead (headphone OK). I've suspected and replaced the battery cell.
>   > > > > > > I was able to run the self tests up to test #5 (analog inputs), but I have
>   > > > > > > no foot controller to complete this stage.
>   > > > > > > I checked the PSU and the voltage source on the main board (+2.5V, +7.5V
>   > > > > > > and +5AV) and everything is OK.
>   > > > > > > I suspect a signal is missing on the sub-CPU (6805), or a defective RAM.
>   > > > > > > I picked up the schematic and the service manual on Dave Benson's site,
>   > > > > > > but it seems to be altered after page 20. All other services manual I found
>   > > > > > > on the web has the same issue. Does anyone have a full copy of it?
>   > > > > > >
>   > > > > > > Thanks,
>   > > > > > > François
>   > > > > > >
>   > > > > > > 
>   > > > > > >
>   > > > > >
>   > > > >
>   > > >
>   > >
>   >
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