Korg Poly 800 wont turn on after battery replacment

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Korg Poly 800 wont turn on after battery replacment

Postby demon » Thu May 04, 2017 1:28 am

Ive had this Korg since somewhere around 1984. I got it for christmas when i was 12 or 13. Its been in the closet for a long time. My son wanted to get it out. he is very talented and can play damn near anything. We plugged it in and it turned on but had no sounds . I remembered the cassette tape that came with it but I have no idea where that is so i went on line and found tis awesome site and was able to download the sounds and the manual. Followed the instructions and messed with the volume and it worked! we were so excited! I went to the store and bought c batteries for it and put them in but as soon as he turned it off the memory was gone. so back to the forums and found that the poly 800 2 has a watch battery for memory inside. I pulled it apart and this one has the battery. Got a new battery today and attempted to solder the batt in like it came without a batt holder. I realize it was probably a bad idea to try and solder on the new battery. any way the battery still had 3 volts and i soldered it back in the Korg no prob. slid the c batteries in and the switch was already on . it was lite up. I turned it off and it wouldnt turn back on . no lights at all. tried plugging it in and nothing. pulled it back apart to check the new soldered in batt so i just pulled it out . i read on someone else's post that it wont light up without the batt so we just held some wires on another new batt and i touched them to the soldered spots. still nothing. We are so bummed! any idea what I can do?
Last edited by demon on Thu May 11, 2017 1:36 am, edited 1 time in total.
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Re: Korg Poly 800 wont turn on after battery replacment

Postby Rasputin » Thu May 04, 2017 3:20 am

Batteries without soldering lugs can explode if you try to solder them in. You're lucky that didn't happen. In the future I highly suggest getting a proper holder to solder in and then future battery changes will be effortless. You also won't have to worry about a mini-bomb exploding in your face.

But enough public service announcement lecturing and on to the troubleshooting...

My rules of troubleshooting are:

1) Get the proper tools. You've got at least a soldering iron, but do you have a multimeter?
2) Get as much info as you can -- finding the schematics and service manual, if possible. Asking for help here was a good idea. Here are the schematics and service manual:

Original model: https://drive.google.com/open?id=0B3OQk ... Wl4RndWMEU
Mark II: https://drive.google.com/open?id=0B3OQk ... VNqU3Zxd2M

Since you have a lithium battery, I'm pretty sure you've got the Mark II, but I've included the original as well, just for giggles.

3) Think about what stupid thing(s) I did that could have broken it or made the existing problem worse :)

Are you sure you got the polarity correct when you installed the new battery? How was the behavior the first time it was turned on with the battery replacement? How long did you use it for before switching it off?

How did you remove the old battery? By desoldering or cutting the leads? I ask because each method has its pitfalls. If you tried to cut the leads with snips then there's a chance you accidentally cut a trace. If you desoldered it then you could have lifted a pad or overheated a nearby component.

Also, did you wrap the new battery and wire leads with electrical tape or some other insulator? If you left it free floating in the synth then there's no telling what it could have touched and shorted out.

Do the C batteries still have the proper voltage? Are you sure the AC adapter you used was the correct voltage, amperage and polarity?

As far as more technical troubleshooting goes, the places you'll want to look are mainly the power input, the RAM, and then the CPU. After you verify that your batteries and power supply are all correct and working, you'll need to see that the power is making its way to the proper places inside the synth. Obviously if the power isn't making it to the ICs then the synth won't work at all, so power is the place to start your investigation.

A good place to check for +5VDC being present on the board would be the CPU. If there is no voltage there then you've got an issue. You should have an Intel 80C85, and you'll want to look at pin 40. That's the input for the CPU's supply voltage.

You'll also want to check that the RAM which holds the patches is getting power from the coin battery. This should be NEC 4464C [64K] (I think).

On the RAM chip, pin 28 should be its supply voltage input. This should be +5VDC when the synth is powered on. Even when powered off, the lithium coin battery should be keeping the RAM alive, so there should be voltage present at that chip. That's a good way to troubleshoot if the coin battery is working or installed properly because the RAM should at least stay at the same voltage as the lithium battery which is 3.2VDC or so, but anything 2+ volts is okay. The RAM will keep the patches correctly as long as the battery doesn't fade below 2V and as long as the mainboard is not disconnected.

If the RAM doesn't have voltage present from the battery, check that the battery voltage is making it to and through D15 which is a diode that should be close to the coin battery. If it's on one side but not the other then that diode is probably shot. If it's making it past the diode then check to see if the battery voltage is making it to the header that leaves that PCB. If so, then make sure it makes it through the ribbon cable and onto the other PCB.

It's possible that if you reversed the lithium battery polarity then the RAM chip is toast. It is designed to handle up to +7V, but only a half volt in the negative range, so a flipped battery would bring it into -3V range which might kill it. Not an impossible part to get, and not super expensive ($15-20, maybe less if you hunt) but replacing it will be a challenge unless you have lots of experience in desoldering DIPs.

So... yeah, keep us informed as to your progress.
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Re: Korg Poly 800 wont turn on after battery replacment

Postby madtheory » Thu May 04, 2017 8:47 am

Excellent advice from Rasputin. Especially "3) Think about what stupid thing(s) I did that could have broken it or made the existing problem worse " IMO that's number 1!! So make sure you did not disconnect any flying leads of the boards to the body of the synth, and between boards. Reseat any ribbon connectors.

Hopefully you didn't overheat components near the battery.
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Re: Korg Poly 800 wont turn on after battery replacment

Postby demon » Thu May 04, 2017 9:53 am

I can't tell you how grateful I am for the help! There's hope! I have a multimeter but I'm much better using it on cars to figure stuff out than electronics. But I am good at following instructions. My son was plugging in the power cord while i was putting in the c batteries. I had the batteries in first and that's when it lit up cause the switch was all ready on so then I shut it off and turned it right back on and it didn't light up. I can't remember if he had it plugged in right then or not and our power cord has the connector on the end that can be reversed for polarity. I don't think it was backwards but its possible. It was only on for a few seconds when we tried to turn it back on after the coin batt swap. It says korg poly 800 and doesn't say 2 anywhere. I've read that the 2's had the coin batt and not the originals but this has the batt and its an original. The first thing I did when it wouldn't turn back on was check the polarity of the coin batt
I even took a pic of the old one before I pulled it to make sure I didn't screw things up. It was right. I pulled the yellow band off the old one and put it on the new batt as well. Nothing was touching anywhere. I made sure of that. Right now the coin batt is out. I will get a holder for it and put it back in. I guess I have to have it in to make it work anyway right? As soon as I get home I will check those things for the power supply. Thanks again. Really appreciate the help
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Re: Korg Poly 800 wont turn on after battery replacment

Postby demon » Thu May 04, 2017 9:56 am

Also when I soldered the batt in and removed the old one I did it very quick so i don't think it overheated and where else. Soldering to the batt was difficult , and stupid as h**l, but soldering back to the solder was super easy
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Re: Korg Poly 800 wont turn on after battery replacment

Postby Weirdofromouterspace » Thu May 04, 2017 10:58 am

demon wrote:It says korg poly 800 and doesn't say 2 anywhere. I've read that the 2's had the coin batt and not the originals but this has the batt and its an original.


Only the very first specimens of the Poly-800 (I) didn't have the coin battery, they added it shortly later on. So that's perfectly normal and in no way unusual. Mine has it as well.

You can see the differences between the Poly-800 and the Poly-800 II here - the II is somewhat darker and bears more blue rather than green:

http://www.vintagesynth.com/korg/poly800.php
Don't forget to TURN ON THE SYNTHESIZER. Often this is the reason why you get no sound out of it. - ARP 2600 manual, 1971
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Re: Korg Poly 800 wont turn on after battery replacment

Postby madtheory » Thu May 04, 2017 11:32 am

demon wrote: I can't remember if he had it plugged in right then or not and our power cord has the connector on the end that can be reversed for polarity. I don't think it was backwards but its possible.

OK get the service manual as Rasputin suggested. Check the power input circuit. We will hope it has a protection diode and that has been killed. Easy to replace that. However, if it doesn't have a protection diode you're looking at some fairly high level circuit diagnostics around the supply input, and you'll be praying that nothing further down the line took a hit.
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Re: Korg Poly 800 wont turn on after battery replacment

Postby Weirdofromouterspace » Thu May 04, 2017 12:28 pm

madtheory wrote:OK get the service manual


Link service: https://elektrotanya.com/korg_poly_800. ... nload.html
There are other sources as well :).
Don't forget to TURN ON THE SYNTHESIZER. Often this is the reason why you get no sound out of it. - ARP 2600 manual, 1971
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Re: Korg Poly 800 wont turn on after battery replacment

Postby Rasputin » Thu May 04, 2017 1:59 pm

Weirdofromouterspace wrote:
madtheory wrote:OK get the service manual


Link service: https://elektrotanya.com/korg_poly_800. ... nload.html
There are other sources as well :).


Like the links I already posted above ;) But hey, there's no such thing as overkill when it comes to hosting. Never know when something will be taken offline, right?

Additional hints for the OP:

If it is the original model and not the mark ii then the RAM will be a 16K Hitachi HM6116 chip instead of the NEC, but the principle still stands -- VCC is pin 24 and supposed to be at 3~5V.

The CPU is also slightly different but pin 40 is supposed to be 5V, so that's all the same too.

There is a protection diode. I believe it is D2. I would look there and also carefully at Q1 which is a transistor.

Edit: Mooger just cross-posted me, ha. Pay attention to him :)
Last edited by Rasputin on Thu May 04, 2017 2:10 pm, edited 2 times in total.
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Re: Korg Poly 800 wont turn on after battery replacment

Postby Mooger5 » Thu May 04, 2017 2:07 pm

Can anyone find the memory backup cell in that schematic. I think that version doesn´t feature the update, as it looks like the backup is done by the power batteries. The coin cell should be located before point F pictured above the memory chip IC21. Diode D15 must still be there to prevent the cell from being "recharged".

The main protection diode is D2. Same scheme as the SH-101. In case of accidental reversed polarity the diode creates a path of lower resistance but if it breaks open the reverse DC will flow through the rest of the circuit making a kill until the next weakest link brakes apart. IDK why is this scheme implemented even if the synth is battery powered. Most pedals that I know don´t use any protection because a 9V battery connector is protection enough; you can´t plug a 9V cell in reverse unless using sticky tape or something; no one is that stupid. The pedals that use it though, have the diode connected in series: if the polarity is correct the current will flow; if it´s not, or if the diode breaks open, it won´t. It´s that simple. I´m sure there will be a good explanation, but right now I don´t know why didn´t they use this better protection scheme, even in a battery powered device. What difference should a loss of half of a volt make??

Anyway other possible culprits could be the transistor Q1 and/or zener Q4. If either of them fail the DC won´t have a return path and the synth won´t power on.
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Re: Korg Poly 800 wont turn on after battery replacment

Postby demon » Thu May 04, 2017 11:57 pm

ok finally got home to do this! I dont know what im doing! but i can follow instructions perfectly! I checked the D2 diode first. i do sorta understand that a diode lets the electricity flow one way but not the other. But i dont know exactly how to check the voltage flow thru it . i did check continuity both ways by switching the multimeter leads around....if thats the right way to do it, i dont get continuity either way so im thinking this is it . well maybe. Can you tell me exactly where to put both ends of the multi meter?
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Re: Korg Poly 800 wont turn on after battery replacment

Postby demon » Thu May 04, 2017 11:59 pm

also i tried looking at the schematic you said to download. the way i look at it , it seems that the d2 diode is only for the power cord and not the c batteries? i have the c batteries in it now so if this was the case it should work whether or not the plug is working? just trying to understand. again thanks so much
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Re: Korg Poly 800 wont turn on after battery replacment

Postby demon » Fri May 05, 2017 12:06 am

"Anyway other possible culprits could be the transistor Q1 and/or zener Q4. If either of them fail the DC won´t have a return path and the synth won´t power on."

also how do you test these? i see where they are but have no idea what they are or how they work
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Re: Korg Poly 800 wont turn on after battery replacment

Postby Rasputin » Fri May 05, 2017 1:33 am

demon wrote:ok finally got home to do this! I dont know what im doing! but i can follow instructions perfectly! I checked the D2 diode first. i do sorta understand that a diode lets the electricity flow one way but not the other. But i dont know exactly how to check the voltage flow thru it . i did check continuity both ways by switching the multimeter leads around....if thats the right way to do it, i dont get continuity either way so im thinking this is it . well maybe. Can you tell me exactly where to put both ends of the multi meter?


If your multimeter has a specific diode test then you can measure the actual voltage drop across the diode both ways. Ordinarily, the diode will function as open with the probes in one position (red on one side, black on the other) and then a drop when the probes are reversed.

If the diode is open then it will not pass anything either way. So regardless of probe orientation then no voltage can go through it because it's no longer conductive. It's like cutting a trench across the middle of the highway -- no traffic.

If the diode is shorted then it will have a voltage drop regardless of probe orientation.

Think of it this way: A proper diode is like a door that only opens one way. An open diode is like a locked door. A shorted diode is like a double-action (bi-swing) door that goes both ways. Cue the dating jokes :)

If your meter only has a resistance test (continuity test is just a form of resistance test on most meters, really) then a proper diode will show infinite resistance with the probes one way, and only some resistance the other way.

A bad diode will show the same value regardless of probe orientation because it's either letting nothing through at all (open) or it's letting the same thing through both ways. That can be no resistance or some resistance, it doesn't matter, because the diode is supposed to be asymmetrical by design.

A continuity test just measures resistance as an absolute form. If the resistance is really high then it's counted as no continuity and if it's really low then it's counted as continuity. A lot of meters actually show the resistance anyway when doing a continuity test, so it's just a dumbed down resistance test with typically an audio cue to go with it.
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Re: Korg Poly 800 wont turn on after battery replacment

Postby Rasputin » Fri May 05, 2017 1:43 am

demon wrote:also i tried looking at the schematic you said to download. the way i look at it , it seems that the d2 diode is only for the power cord and not the c batteries? i have the c batteries in it now so if this was the case it should work whether or not the plug is working? just trying to understand. again thanks so much


I think Mooger touched on this idea.

Let's assume that you were powered off the C batteries until the AC adapter was plugged in (with the wrong polarity) a split second before you went for the off switch.

The AC adapter fried the diode and also some other component (Q1?). So now you've tested the protection diode and it looks bad. That doesn't prevent the batteries from working, but a bad Q1 would (which was collateral damage).

So if you fix Q1 then you might get battery operation back, but then D2 needs to be replaced in order for AC power to work too.

These are just general assumptions, but it sounds quite plausible. Based on what you've said so far, that sounds like it could be what happened. And I do agree it sounds like D2 is bad from what you've said about your testing.

Not that this will be electrically conclusive proof, but look at Q1 and give it a smell. Anything make you think it is burnt?

Good news is that if these are the faults, it will be an easy $10 repair for the battery holder, a diode or two, and a couple transistors.
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