Poly800 first eight keys muddled with button actions

Pulling out your hair? Don't know what to do or where to go? Ask in here.
Forum rules
READ: VSE Board-Wide Rules and Guidelines

If your Help request has been solved, please edit your first post in order to select the Image Topic Icon to let others know your topic has been solved.
TimeOut4Fun
Newbie
Newbie
Posts:7
Joined:Tue May 18, 2021 2:47 am
Gear:Farfisa VIP-600
Poly800 first eight keys muddled with button actions

Post by TimeOut4Fun » Tue May 18, 2021 3:38 am

Hoping someone can shed some light on this.
I bought this mk1 poly800 knowing full well it had issues.
That said, when i first obtained it, the first 8 keys were triggering other functions,
and it needed to have the patches programmed, which was a little tricky getting the tape in level right,
but I was able to get it partially programmed and check the rest of the functionality.
The first 8 keys are misbehaving but all the others work fine.
and the joystick and sequencer and numerical and patch parameter buttons were working too, but....
I thought it must be a problem with the keyboard and switch scanning system
so I replaced IC34, a 3 to 8 line demultiplexer- 40H138, with a modern cmos equivalent
at that point the joystick and the sequencer buttons were no longer responsive.
And the original problem persists - the first 8 keys still activating other functions.
C1 does appear to function normally , C#1 starts the sequencer,
D1 disables both poly mode and hold mode, D#1 stops the sequencer,
E1 appears to now be triggering the extreme of the joystick pitch bend down
F1 is enabling the Tape mode, and F#1 is cycling the program step up function
and G1 appears to play a different patch than what is selected and a different pitch than the key would
indicate (it plays a low C) with the extreme of the vcf applied to it.

I should note that most of those 8 keys are also playing the appropriate note in addition to the other functions they are activating, with the exception of F1 which makes no sound since tape mode is enabled when depressed, and G1.

After replacing IC34, and still having issues I replaced IC33, a 3 state octal buffer- TC40H240(also part of the key and switch scanning system), which did not change anything.
Any suggestions for what to try next, or why replacing the demux caused more problems?
Thank you in advance.

TimeOut4Fun
Newbie
Newbie
Posts:7
Joined:Tue May 18, 2021 2:47 am
Gear:Farfisa VIP-600

Re: Poly800 first eight keys muddled with button actions

Post by TimeOut4Fun » Thu May 27, 2021 6:10 pm

Also replaced IC 29, the address decoder, but that made no difference.
Just to rule out a problem with the new demultiplexer chip, since I had lost the joystick and sequencer button functionality after replacing it initially, I put the original 40H138 back in IC 34, but still no change.
Does anyone think I might have a problem with the CPU? or am I barking up the wrong tree...
Thx

User avatar
madtheory
Supporting Member!
Supporting Member!
Posts:5488
Joined:Mon May 01, 2006 12:45 pm
Real name:Tomas Mulcahy
Gear:Wurlitzer Opus 1536, Model F, Morovdis Arpeggiator, Maplin My First EQ, Jeff Wayne Thunderchild rack, Thermostat, Buck Owens' Moog.
Location:Cork, Ireland
Contact:

Re: Poly800 first eight keys muddled with button actions

Post by madtheory » Fri May 28, 2021 12:05 pm

The first thing to do would have been to check how it works via MIDI in. If it functions normally that way then you know it's not the CPU, it's somewhere between keyboard matrix and where that and front panel logic are input to CPU. Doesn't seem symptomatic of a buffer, as you have ascertained by replacing that. I'd be looking at any mux/ demux chips there but it's more likely a failed capacitor upsetting a chip than a chip itself. You won't know until you have datasheets and have done a bunch of testing. Try to avoid shotgun chip replacement. Figure the thing out logically. It will take days :)

TimeOut4Fun
Newbie
Newbie
Posts:7
Joined:Tue May 18, 2021 2:47 am
Gear:Farfisa VIP-600

Re: Poly800 first eight keys muddled with button actions

Post by TimeOut4Fun » Sat May 29, 2021 2:51 am

Thanks MadTheory,
The notes in question function properly when receiving external MIDI, so I'll rule out the CPU.
I will look more closely at the decoupling caps in the keyboard panel switch input circuit.
Here is the area I've been focusing on
AFAICT the kbd and panel switch inputs are fed directly to the CPU via the 40h240 buffer output address 0-7
poly800keyboard-switch.jpg
poly800 kbd switch input circuit

User avatar
madtheory
Supporting Member!
Supporting Member!
Posts:5488
Joined:Mon May 01, 2006 12:45 pm
Real name:Tomas Mulcahy
Gear:Wurlitzer Opus 1536, Model F, Morovdis Arpeggiator, Maplin My First EQ, Jeff Wayne Thunderchild rack, Thermostat, Buck Owens' Moog.
Location:Cork, Ireland
Contact:

Re: Poly800 first eight keys muddled with button actions

Post by madtheory » Sat May 29, 2021 9:38 am

Ya good call on the decoupling caps. If that doesn't throw up an issue, you'd need a logic analyzer to see what is going in and out of the 40H240. It's possible for a chip to partially fail. You could take it out and test it on the bench to rule it out (rather than simply replacing it) because the replacement may be faulty too.

Personally I would not give this the time, I'd simply use it via MIDI. Well personally I would take any Casio home keyboard over a Poly 800 but that's just my personal taste :lol:

User avatar
meatballfulton
Moderator
Moderator
Posts:6189
Joined:Wed Apr 13, 2005 9:29 pm
Gear:Logic Pro X

Re: Poly800 first eight keys muddled with button actions

Post by meatballfulton » Sat May 29, 2021 3:04 pm

I'm with Madtheory. When I had a Poly 800, I always played it from my Motif's keyboard.
I listened to Hatfield and the North at Rainbow. They were very wonderful and they made my heart a prisoner.

User avatar
madtheory
Supporting Member!
Supporting Member!
Posts:5488
Joined:Mon May 01, 2006 12:45 pm
Real name:Tomas Mulcahy
Gear:Wurlitzer Opus 1536, Model F, Morovdis Arpeggiator, Maplin My First EQ, Jeff Wayne Thunderchild rack, Thermostat, Buck Owens' Moog.
Location:Cork, Ireland
Contact:

Re: Poly800 first eight keys muddled with button actions

Post by madtheory » Sat May 29, 2021 3:12 pm


TimeOut4Fun
Newbie
Newbie
Posts:7
Joined:Tue May 18, 2021 2:47 am
Gear:Farfisa VIP-600

Re: Poly800 first eight keys muddled with button actions

Post by TimeOut4Fun » Sat May 29, 2021 3:54 pm

:giveheart: :giveheart: :giveheart: :drinks:
Love that video!
I just bought it to learn more about synthesizer repair, and the sound brings me back to the roller skating disco of my youth.
"I'm the operator with my pocket calculator
By pressing down a special key it plays a little melody."

User avatar
madtheory
Supporting Member!
Supporting Member!
Posts:5488
Joined:Mon May 01, 2006 12:45 pm
Real name:Tomas Mulcahy
Gear:Wurlitzer Opus 1536, Model F, Morovdis Arpeggiator, Maplin My First EQ, Jeff Wayne Thunderchild rack, Thermostat, Buck Owens' Moog.
Location:Cork, Ireland
Contact:

Re: Poly800 first eight keys muddled with button actions

Post by madtheory » Sat May 29, 2021 4:35 pm

Cool! Please do keep us posted on your progress with it :)

TimeOut4Fun
Newbie
Newbie
Posts:7
Joined:Tue May 18, 2021 2:47 am
Gear:Farfisa VIP-600

Re: Poly800 first eight keys muddled with button actions

Post by TimeOut4Fun » Mon May 31, 2021 9:14 pm

You know actually... when controlling the poly with an external midi kbd, it isn't initially playing properly.
All notes on all patches play with the vcf on full tilt, this happens on the poly 800 stand alone as well . I'm able to get rid of that behavior for both internal kbd and external midi kbd by holding the low g on the poly (which is the erroneous key that always plays a low c with vcf on full tilt) and simultaneously holding several keys in the unaffected portion of the poly kbd.
So my question is.. in its initial state, the poly800 is not functioning 100% properly with external midi control, so does that bring the cpu back into question?

User avatar
madtheory
Supporting Member!
Supporting Member!
Posts:5488
Joined:Mon May 01, 2006 12:45 pm
Real name:Tomas Mulcahy
Gear:Wurlitzer Opus 1536, Model F, Morovdis Arpeggiator, Maplin My First EQ, Jeff Wayne Thunderchild rack, Thermostat, Buck Owens' Moog.
Location:Cork, Ireland
Contact:

Re: Poly800 first eight keys muddled with button actions

Post by madtheory » Tue Jun 01, 2021 1:18 pm

Depends on where the MIDI comes in, does it go through that same buffer chip?

TimeOut4Fun
Newbie
Newbie
Posts:7
Joined:Tue May 18, 2021 2:47 am
Gear:Farfisa VIP-600

Re: Poly800 first eight keys muddled with button actions

Post by TimeOut4Fun » Wed Jun 02, 2021 8:05 pm

No, the 8 bit MIDI data bus is shared by the buffer's output, but not processed by it.
I've highlighted the data bus here in yellow from the MIDI chip to/from the CPU
Poly800MidiDataBus.jpg

User avatar
madtheory
Supporting Member!
Supporting Member!
Posts:5488
Joined:Mon May 01, 2006 12:45 pm
Real name:Tomas Mulcahy
Gear:Wurlitzer Opus 1536, Model F, Morovdis Arpeggiator, Maplin My First EQ, Jeff Wayne Thunderchild rack, Thermostat, Buck Owens' Moog.
Location:Cork, Ireland
Contact:

Re: Poly800 first eight keys muddled with button actions

Post by madtheory » Thu Jun 03, 2021 2:37 pm

OK well I could be wrong but in that case it would seem obvious that the CPU has a problem. Get the data sheet and a logic analyzer and check that it matches up. Before replacing that though, I would look at replacing the EPROM where its instructions are stored. Because that's more likely to have aged than the CPU itself.

TimeOut4Fun
Newbie
Newbie
Posts:7
Joined:Tue May 18, 2021 2:47 am
Gear:Farfisa VIP-600

Re: Poly800 first eight keys muddled with button actions

Post by TimeOut4Fun » Thu Jun 03, 2021 5:10 pm

That sounds like a reasonable approach. I had looked at some of those EPROMs on ebay.
Thank you for your insight.

Now I feel like I am getting somewhere!
Image

User avatar
madtheory
Supporting Member!
Supporting Member!
Posts:5488
Joined:Mon May 01, 2006 12:45 pm
Real name:Tomas Mulcahy
Gear:Wurlitzer Opus 1536, Model F, Morovdis Arpeggiator, Maplin My First EQ, Jeff Wayne Thunderchild rack, Thermostat, Buck Owens' Moog.
Location:Cork, Ireland
Contact:

Re: Poly800 first eight keys muddled with button actions

Post by madtheory » Thu Jun 03, 2021 6:46 pm

:lol:

Post Reply