Circuitbenders Forum
Circuitbenders Forum => Parts, Components, Unbent machines & Junk => Topic started by: Circuitbenders on June 15, 2009, 04:20:49 PM
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I've got a Korg Poly800 mk2 that refuses to do anything ither than produce filtered noise. I've been lead to believe that this is a fault with the firmware eprom.
I've taken a dump of the eprom in there which was labelled as an HN4827128G-25 and then erased it, and that worked fine. When i click 'blank test' on my willem programmer software it comes up that the device is blank and if i read it every entry is FF.
I've got a dump of a working Poly 800 mk2 .bin file off the net but thats labelled as being from a 27C128 eprom and won't write to the eprom i have. I don't know if this is because the one i have is damaged and can't be written to, or because its the wrong kind of eprom for that file.
Is the HN4827128G-25 actually compatible with a 27C128 .bin file or has the person who uploaded it just labelled it wrong? It seems unlikely there would be different eproms in different Poly 800 mk2's. If the eprom i have is actually damaged an can never be written to, should i be getting hold of a 27C128, trying to track down a HN4827128G-25, or looking for some eqivalent thats easier to get hold of?
If anyone has a Poly 800 mk2 and has faciliies to take eprom dumps could you do me a copy and send it to me?
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The actual type of EPROM isn't important to the image. You can use a 27C128 just fine. What *is* important is that you select the correct type of EPROM when you're burning, because a 27C128 requires a different programming voltage from a 27128.
If the EPROM you have only reads back 0xFF then either it has been erased or it is knackered.
You can use any EPROM that is 128kbits or larger, but for a 27C256 (for example) you'd need to burn the image twice (low half and high half), or strap the extra address line low.
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so in theory an image that appears to have been taken from a 27C128 should write fine to a 27128, which i'm assuming is what my HN4827128G-25 actually is, as long as i have 27128 selected when i write it?
I'm hoping that the eprom i have is reading FF because its erased. It did have a load of data on it until i erased it with my UV box but i can't seem to write to it for some reason, it does verify as OK but that doesn't seem to mean that much. Could trying to write to it as a 27C128 have damaged it in any respect or would it just not write?
Typically i have a few 27C256's but I think i'll have a hunt through some parts boxes for another 27128 before attempting to use one of those.
(EDIT)
I've just read on some wiki article that C eproms need 6V to write and non C ones need 5V but i've written plenty of 27C256's fine at 5V, in fact i only just noticed that my programmer has a jumper to select between 5V, 5.6V and 6V. Is it really that important?
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Yes, extremely important. Also the programming voltage applied to the Vpp pin must be right - for an oldskool 27128 EPROM it must be 21V, for a 27C128 or 27128A it must be 12.5V. Too high a Vpp will zorch the chip, too low will leave it utterly nonplussed by your attempts to gain its attention.
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for an oldskool 27128 EPROM it must be 21V.
Ahhhh, thats got it, i was trying to do it at 12.5v.
I've managed to rewrite the firmware to the eprom and stuck it back into the Poly800 and its made no difference whatsoever. I guess its either something else thats causing the problem or the eprom isn't working quite as it should, although i'm guessing i wouldn't actually be able to write to the eprom and it wouldn't work as far as it does if it was that knackered.
Back to the drawing board. :-\
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Hi
I am in the middle of repairing a KORG POLY800 II at the present time. This one has died although all voltages are present on the main circuit board and the main cpu appears to be giving some activity with some signals lost. I have just ordered a MSM80C85 OKI uP and also the TIMER/MEMORY PIO chip 81C55 this should bring this thing back to life. My question is, where can you get the EPROM .bin file for the main eprom?? can anyone help?? Semi Company "LITTLE DIODE" Provided the uP and the PIO chips. I have a multi programmer called GALEP and hopefully use this to burn the new software onto a replacement eprom.
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You might want to look at the Poly 800 Yahoo! group. The .bin files for the various flavours of Poly 800 are out there.
Are you sure it's the CPU and PIO that have failed? They're normally pretty reliable. How did you test them?
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What are the exact symptoms of whats gone wrong? I've repaired a few Poly's now and the problems are almost always something in the power supply or some logic IC dying.
I've uploaded the poly800 mkII main eprom file here if you need it
http://www.mediafire.com/?ndjxebmmgmj (http://www.mediafire.com/?ndjxebmmgmj)
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Thankyou so much for the POLY 800II eprom bin!!!
I have two service manuals, POLY800 & POLY800II. For some reason the output waveforms are omitted from the poly800II manual. As the cpu section is almost identical i used the waveform data from the 800 manual. The 800II in question is giving no sound and no display. I was amazed at how complex the the power circuit is in this thing!!. I have tested every aspect of the power section and this appears to be ok. 5V Lines are present and also -5v line is present, nothing being pulled low. The +/- Supplies are also correct for the analogue sections. Using a 20Mhz scope i checked the communication between the cpu and pio and it would seem as though one of the timing lines is missing also one of the reset lines is missing. With the cpu removed reset line works. Most of the resets are generated by external circuits. I managed to get the pio and cpu very cheaply so i will try this. I will post and tell you how i get on.
THANKS AGAIN!!
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I've had a problem with the timing clocks missing before, where one of the clocks for the M5232 was missing but in that case it did start up but neither DCO would make any sound.
The issue on mine was is with one of the logic IC's at IC16, IC17, or IC18 which generate the clock
One of the weird things i've had with a poly800mkII was with a version of the main board with EMI in the serial number which appeared to have both an analogue and a digital ground, unlike most versions. As far as i could make out the grounds were linked via the shielding under the board so if the board wasn't screwed into place with the shielding connected to the ground then the thing just wouldn't start up.
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You are correct, the shielding is also a earth bridge. I made sure that this was fitted correctly although you can get caught out by this. Sorry i am posting messages on the circuit benders forum regarding the repair of a poly800, there are probably other forums that can help. I am looking at adding some bells and whistles once this thing is repaired though.
THANKS!!!!!!!!!
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Managed to import the poly800II EPROM bin file to the GALEP programmer, have looked at the code and all is good!
Going to do a comparison of the original backup just to see if the code is the same. 27c128 EPROM i could not find in my workshop managed to purchase one on ebay £1.40!!! Going to cook and burn the chip monday.I will let you know if you like if there is life!!
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If you have a 27C256 or 27C512 EPROM then you can use that by blowing the image either twice or four times, blowing it so it sits in the top 128kbits of the EPROM, or ensuring that the extra address lines are pulled low when you plug it into the Poly 800.
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I suppose i could have done that as i have a surplus of 256,512,1001 eprom variants. It is down to the sophistication of your programmer and software i suppose. I could have copied the data several times and pasted the data at certain areas within the chip. I did not think though that £1.40 was bad for a 27c128 . I am still waiting for the chip to be delivered, as soon as i see sight of it i will post the outcome. I know it has been said that the uP and PIO in the poy800 II are bomb proof but every test i have undertaken has proved that it cannot be anything else at fault. All resets and voltages are present including all the clocks. The outcome of the comparison was device mismatch at quite a few memory areas meaning that the bin file is an update or my original data is corrupt. There is a ref sticker over the eprom window, i will post this when i get home.
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Cleared the data from the eprom i bought from ebay, burned the poly 800II data to the chip ,installed in the synth and low and behold.......DEAD!. Have not recieved the cpu or the pio as of yet, as soon as these are recieved i will post results. The original poly800 eprom's number was 851006. I have read many times on the web that the eproms in the poly become corrupt and lose data.. I do not think this is the case with this synth. :-\
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To be honest i didn't think it would be. :-\
I think that dump was from a 851005 chip. I do have a 851006 eprom as well somewhere but i can't really see it making much difference.
If theres any readings you need from a working Poly800 mkII i do have one here i could test for you.
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Close inspection of the power supply in the POLY800II i can now see how things function but if anybody knows the circuit in question am i right in saying that the -5v supply line is generated by using a HARTLEY ocillator?? If not is there anyone out there that can explain how this part of the circuit works?? I can see that this must be an ocillator of a sort because there is a stable DC feeding into the centre tap. On the seconary side there are four diodes creating a reversed bridge of which the output is fed through an ELEY choke then the final -5. Transistor Q7 clamps the centre tap of the coil being shunted by D7. The value of D7 is not clear in the schematic (68IL ZENER). D794 although using a meter this device checks ok but when mounted in the board the transistor overheats. There does not seem to be any information on the choke/transformer.
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The wee oscillator thing for the -5 supply seems reasonable. If the transistor is overheating, it's possible that something is loading down the -5V rail - check you didn't put the zener in "backwards" with the anode to positive ;-)
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Thankyou for your reply gordon.
The ZENER in question has not been removed from the board, i know that sometimes cold checks just don't cut the mustard, got to remove the component and test with suitable dropper on the the bench. Got a nice forward drop on it though so i am assuming that this component is ok. The Drive transistor responsible for the switching is quite a hefty power type driving the coil under some kind of resonance. What the korg designers have added after the -5v is developed is a small smoothing choke rated at a few uH, with this component taken off the board it allows you to completely isolate the -5 supply line, when i do this the transistor does not overheat meaning there is a load elsewhere. Only problem is the -5v supply line with no load condition is now at -2.86v which is obviously incorrect. The analogue circuits require a 10V P/P swing to work. Close inspection of the schematics show that even some of the MC4051 Multiplexer chips use this supply line also. You mentioned in previous posts that most of the problems you have experianced with the poly800 are with the supply lines, what type of problems have you experianced gordon??? Everything regarding power seems to be ok on the circuitboard apart from this -5 line and i cannot believe that this line alone will render the poly800 dead. I have voltages just about everywhere else and i would have expected some activity. Do you have any information or spare eley resonance choke as i believe the over heat may have caused a small short in the coil??? I have seen better circuits for the development of a -5v supply line, why korg have done it this way is beyond me.
THANKYOU FOR YOUR HELP
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Normally the 4051s either don't switch at all or get stuck on one output. I've never heard of them drawing excessive current but I suppose it's not impossible.
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i'm afraid i will join this club :-[
got a broken poly800 mk1 in a trade. the guy said it stopped working after doing the battery mod
(not the one described in this site, but another one) i discovered he forgot to cut a trace, so i did that,
but it didn't help anything. the situation is like this : no display (sometimes strange symbols) at the output
only filtered noise. the moogslayer mod, already there, does function.. :-\
i am very much afraid that the firmware has been whiped..
any ideas ?
would it be possible to hack the thing into a filterbank or something, to still use the analogue part of it or something?
cheers nochtanz
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Check for the voltage and the clock signals going into the main synthesis chip. It sounds like you might not be getting proper power to the M5232 to me.
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so there's hope still.. thanks! i'll have to wait for aproval of poly800 groups membership, so that i can check pinout of the m5232 ::)
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Also make sure the shielding is connected everywhere that it should be. As is says somewhere else in this thread, there is an analogue and a digital ground which should be connected together via the shielding underneath the board. I think i had exactly the display issues you describe while installing some mods on a mkII due the shielding connecting intermittently.
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Check for the voltage and the clock signals going into the main synthesis chip. It sounds like you might not be getting proper power to the M5232 to me.
hmm i checked the volages on the M5232, and they're allright :-\
have to check the shielding a bit better, but so far it seems ok too.. couldn't find a digital ground connection tough