sk-1 auto power off mod

[tuckertota]

Hi, i've tried to disable the auto power off but cannot seem to figure it out. I followed the instructions:

http://electro-music.com/forum/phpbb-files/sk1_apo_bypass_414.pdf

After making the adjustments, the keyboard worked, but still shut off after 7 minutes. I read this on these forums:

http://www.circuitbenders.co.uk/forum/index.php/topic,717.0.html

Somebody mentions that it only prevents the analog section of the keyboard from turing off, so it look like it's on, but when you press the keys you get nothing. This is what is happening to me.

Does anybody know how to successfully disable the sk-1's auto power off?


Thanks..

[djsynchro]

http://www.electri-fire.com/

have a good browse around this dude's site the answer is on there if I remember well

[tuckertota]

Yea, this is where i first got the information. The link i attached is the same tutorial but with people's comments. Some people say they have the same problem as me, the keyboard works but still shuts off after 7 minutes. After searching a bit, i think the definitive answer is that it can't be done. The mod seems to keep the keyboard on, but the processor shuts down no matter what. It probably has a built in timer of sorts. Some people claim to have accomplished disabling the auto-power-off, but they never say how.

[C M O S]

Hi, Just had a look at the schematic for the SK1 and you are correct in your assumption that the 7minute APO signal is under main cpu control. The cpu in question is the MSM6283.01GS LSI. The cpu pin responsible for the APO is PIN 86. At switch on this pin will be held high, if the CPU senses no activity in 7 minutes this pin goes low. This pin connects to TR2's base in the power supply section biasing the transistor into conduction thus switching the supply to the keyboard on. Hope this gives you some kind of clue as to possible control of APO. Here is a link to the service manual download. It is for the tandy concertmate version but still an SK1, this also may help.

http://www.electro-music.com/forum/topic-11486.html

ENJOY

[C M O S]

Looking at many websites and reading many replies on forums it would seem all that is being done here is bias of TR2 forcing the power section to supply current to the analogue & digital sections the problem with this is the cpu will go into sleep mode regardless of power supply condition. Power light will be on but keyboard will not work. Another approach would be to build a small circuit that could be powered from the sk1 supply lines and put it inside the case. If the cpu is looking for activity then at maybe 6 minutes apart a pulse could be applied somewhere in the circuit automatically fooling the microprocessor into thinking it's seen activity keeping the thing running. A small cmos 4060 timer circuit could constructed to supply the needed delayed pulse. Pulse could be current limited then injected at the correct area........JUST A THOUGHT!!!!!!!!!