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Assistance with fixing bad DIY job on Poly800 AC and battery

Assistance with fixing bad DIY job on Poly800 AC and battery

2016-08-31 by jkbarnes@...

Hey guys,


I picked up an old Poly800 with a couple problems. The tuning slider didn't work, the pitch bend on the joystick didn't work, and the unit won't accept AC power. It does run off batteries just fine.


When I cracked the case I found that someone had done a really poor job of installing a battery mod. They soldered in a 1/2 AA Lithium Ion battery but managed to get about 3/4 inch of excess solder from the negative pad of the battery across 5-6 of the traces. They also removed the component at C88. I desoldered the battery and wicked up the excess solder and found that one of the traces was broken (the one immediately below the negative pad in the attached picture). I repaired the trace and got continuity. The tuning slider and pitch bend then started working!


However, I have 2 issues now that I can't seem to sort out myself.


1. Whenever I turn the power off to the synth for longer than about 10 minutes, it loses all its programming. This happens WITH the C-cells still in it. I believe this has something to do with component C88 being removed but I'm not sure. I have ordered the Hawk800 + Atomahawk mods. My understanding is that the mods negate the need for any sort of battery powered memory so do I even need to fix this issue? If so can someone help me ID that component? I'm having a hard time reading the schematic....


2. AC power won't work. Component D2 has been reduced to ash near the AC adapter. There also appears to be some more ham-fisted soldering and I can't tell if there is more wrong than just the burnt component. Can you guys take a peek at the attached picture and let me know what you think? Do I just need to replace component D2? I picked up some 9.1v zener diodes but can someone confirm that this is the proper component?



Thank you,


-J

Re: [korgpolyex] Assistance with fixing bad DIY job on Poly800 AC and battery [2 Attachments]

2016-08-31 by Gordonjcp

On Wed, Aug 31, 2016 at 10:53:11AM -0700, jkbarnes@... [korgpolyex] wrote:
>
> 1. Whenever I turn the power off to the synth for longer than about 10 minutes, it loses all its programming. This happens WITH the C-cells still in it. I believe this has something to do with component C88 being removed but I'm not sure. I have ordered the Hawk800 + Atomahawk mods. My understanding is that the mods negate the need for any sort of battery powered memory so do I even need to fix this issue? If so can someone help me ID that component? I'm having a hard time reading the schematic....
>

The circuit diagrams are readily available (but pretty damn poor quality).

C88 is a 47μF 16V electrolytic, on the diagram it's beside the 6116 memory IC.

The value is not critical. It provides a bit of power to IC21 when there is no mains supply and no battery. The voltage probably isn't too critical either, but at least 16V will be "about right".

>
> 2. AC power won't work. Component D2 has been reduced to ash near the AC adapter. There also appears to be some more ham-fisted soldering and I can't tell if there is more wrong than just the burnt component. Can you guys take a peek at the attached picture and let me know what you think? Do I just need to replace component D2? I picked up some 9.1v zener diodes but can someone confirm that this is the proper component?

D2 is a protection diode that links the centre pin of the on/off switch and the "sleeve". It's "backwards" because it should conduct when you put a positive-centre power supply in to stop the rest of the circuit getting zapped.

Guess what's most likely happened?

So to solve that problem you're likely to need to check out Q1, D4 and friends which is a 9V regulator in the *negative* rail coming from the power supply.

--
Gordonjcp MM0YEQ

Re: [korgpolyex] Assistance with fixing bad DIY job on Poly800 AC and battery [2 Attachments]

2016-08-31 by jkbarnes@...

Gordon,

Thank you. Do you know if I still need to replace C88 if I am installing the Hawk and Atomahawk mods?


I figured someone reversed the polarity. :) Man, they must have had a bad time with their little DIY project. I'll check the suggested components tonight.

Happen to know the specs on D2? I bought 9.1v zener diodes I think they are 1W... gotta check when I get home.

I'm also very wary of the solder job someone has done with the black wire coming off the barrel. Where it is soldered to the board looks like it may have been soldered onto two connections or maybe over another component. Does that wire look like it's at least soldered to the proper pads to you? I keep trying to read the schematic but I can't figure it out.

Re: [korgpolyex] Assistance with fixing bad DIY job on Poly800 AC and battery

2016-08-31 by Gordonjcp

On Wed, Aug 31, 2016 at 12:42:50PM -0700, jkbarnes@... [korgpolyex] wrote:
> Gordon,
>
> Thank you. Do you know if I still need to replace C88 if I am installing the Hawk and Atomahawk mods?
>

No idea, the man himself will tell you that :-)
>
> Happen to know the specs on D2? I bought 9.1v zener diodes I think they are 1W... gotta check when I get home.
>

It's not a zener. Something like a 1N4001 will be fine, it's not really important.

> I'm also very wary of the solder job someone has done with the black wire coming off the barrel. Where it is soldered to the board looks like it may have been soldered onto two connections or maybe over another component. Does that wire look like it's at least soldered to the proper pads to you? I keep trying to read the schematic but I can't figure it out.

I think the list strips attachments. You could post it to imgur or similar.

--
Gordonjcp MM0YEQ

Re: [korgpolyex] Assistance with fixing bad DIY job on Poly800 AC and battery

2016-09-02 by Michael Hawkins

No, you won't need the cap once you install the HAWK. However,...

I do recommend trying to tidy up your little mess completely and make sure that everything works exactly as it should before you install the HAWK.

Two reasons.

1) It's alot easier to troubleshoot problems with the HAWK when everything works as it should. There's nothing worse than trying to help someone troubleshoot a HAWK installation when they tell me that there were other problems already present in the Poly.

2) If anyone ever decided to remove the HAWK, they would end up inheriting those problems.

/Mike


From: "jkbarnes@... [korgpolyex]" <korgpolyex@yahoogroups.com>
To: korgpolyex@yahoogroups.com
Sent: Wednesday, August 31, 2016 3:42 PM
Subject: Re: [korgpolyex] Assistance with fixing bad DIY job on Poly800 AC and battery

 
Gordon,

Thank you. Do you know if I still need to replace C88 if I am installing the Hawk and Atomahawk mods?


I figured someone reversed the polarity. :) Man, they must have had a bad time with their little DIY project. I'll check the suggested components tonight.

Happen to know the specs on D2? I bought 9.1v zener diodes I think they are 1W... gotta check when I get home.

I'm also very wary of the solder job someone has done with the black wire coming off the barrel. Where it is soldered to the board looks like it may have been soldered onto two connections or maybe over another component. Does that wire look like it's at least soldered to the proper pads to you? I keep trying to read the schematic but I can't figure it out.