Korg Poly800/EX800 Users

HCT sometimes works in place of HC but not always due to speed.

From Wikipedia...

The CMOS–TTL logic level problem
Interconnecting any two logic families often required special techniques such as additional pull-up resistors, or purpose-built interface circuits, since the logic families may use different voltage levels to represent 1 and 0 states, and may have other interface requirements only met within the logic family.
TTL logic levels are different from those of CMOS – generally a TTL 
output does not rise high enough to be reliably recognized as a logic 1 
by a CMOS input. This problem was solved by the invention of the 74HCT 
family of devices that uses CMOS technology but TTL input logic levels. 
These devices only work with a 5V power supply. They form a replacement 
for TTL, although HCT is slower than original TTL (HC logic has about 
the same speed as original TTL).


________________________________
From: Martin Ator <cyllall@yahoo.com>
To: "korgpolyex@yahoogroups.com" <korgpolyex@yahoogroups.com>
Sent: Thursday, September 8, 2011 5:35 PM
Subject: Re: [korgpolyex] Tape in Switch doesn't show load on display when activated


  
Ahh, I think now it might actually have been an HCT not an HC, that I tried first. Part number is a little worn



________________________________
From: Michael Hawkins <korgpolyex800@...>
To: "korgpolyex@yahoogroups.com" <korgpolyex@yahoogroups.com>
Sent: Thursday, 8 September 2011, 19:03
Subject: Re: [korgpolyex] Tape in Switch doesn't show load on display when activated


  
What was exact part no. manufacturer for the one that you had in there that didn't work?



________________________________
From: Martin Ator <cyllall@yahoo.com>
To: "korgpolyex@yahoogroups.com" <korgpolyex@yahoogroups.com>
Sent: Thursday, September 8, 2011 9:57 AM
Subject: Re: [korgpolyex] Tape in Switch doesn't show load on display when activated


  
Thanks for your help.

I just got a 74HC240 with a closer spec to the original and it works now.

Martin


________________________________
From: Martin Ator <cyllall@...>
To: "korgpolyex@yahoogroups.com" <korgpolyex@yahoogroups.com>
Sent: Wednesday, 7 September 2011, 17:55
Subject: Re: [korgpolyex] Tape in Switch doesn't show load on display when activated


  
If I ground pin 13 of IC 33, I can get TAPE to show on the display. If I measure the voltage at pin 13 and hit the TAPE Enable switch I can only detect a voltage change of a few millivolts.


________________________________
From: Martin Ator <cyllall@...>
To: "korgpolyex@yahoogroups.com" <korgpolyex@yahoogroups.com>
Sent: Tuesday, 6 September 2011, 23:30
Subject: Re: [korgpolyex] Tape in Switch doesn't show load on display when activated


  
Hi,
I've checked all wires/buttons/switches and they are working. I just programmed in a patch from scratch and tried to write it to memory, but the program enable switch does nothing, and consequently the write button does nothing, but both are working fine as switches/buttons.

This is a machine with some very slight battery damage which corroded the legs on IC33. I'm just checking the pcb now, and it looks like there has been some soldering going on with  DTC 5 so this could have been damaged by excessive heat?. If this was a normal transistor it would be easy to check. I suppose I can look for some voltages changing.
The step up jack worked, so this must mean that DTC 4 is OK?. 

Sequencer write isn't working.
I'll keep looking.
Thanks
Martin



________________________________
From: Michael Hawkins <korgpolyex800@...>
To: "korgpolyex@yahoogroups.com" <korgpolyex@...m>
Sent: Tuesday, 6 September 2011, 21:46
Subject: Re: [korgpolyex] Tape in Switch doesn't show load on display when activated


  
Check the "UP" parameter button and the "4" on the keypad.

If they are OK then check the "Step Up" jack and the "Program Enable" switch functions.

If all of the above are working then simply check the Tape Enable switch itself.

If "Up" and "4" are OK then check the continuity of the wire in connector CN3 wire 11A.

Mike



________________________________
From: cyllall <cyllall@yahoo.com>
To: korgpolyex@yahoogroups.com
Sent: Tuesday, September 6, 2011 2:45 PM
Subject: [korgpolyex] Tape in Switch doesn't show load on display when activated


  
Hi Everyone,
My tape in switch doesn't do anything, so I can't load in the sounds by tape. It should show load on the display. Is the voltage comparator or one of the DTC transistors to blame? Anyone had a similar problem? I don't know if I can test those DTC transistors with a DVM and I don't have an analogue meter.The switch itself works fine but the schematic is difficult to read exactly what's going on. Does the signal end up at any of the Enable pins on any of the chips? I could work backwards then, which might be easier to find the fault.
Everything else seems to work OK.
Thanks
Martin