(A500+) Ctrl + Amiga + Amiga does not work.

[rkauer]

 Checking again the keyboard circuit, the reset line/wire is connected to the pin #8 of the 74LS27 chip on the kb board.

[Protek]

rkauer wrote:
 Checking again the keyboard circuit, the reset line/wire is connected to the pin #8 of the 74LS27 chip on the kb board.

So, stating the obvious here, swapping the chip does the trick?

[rkauer]

Protek wrote:
So, stating the obvious here, swapping the chip does the trick?

 If the chip is faulty, yes.

 Better check the line with a multimeter first (at dc voltage measurement). When the Ctrl+L-Amiga+R-Amiga is pressed, the chip logic issues a "0" (zero) voltage to that pin.

 Simple case of open the Amiga, keep everything in place, turn it on and measure the voltage level on the pin (with and without the key combination pressed). Just be careful to not short the pins on the chip. Better measure the voltage right on the red wire.

[sim085]

rkauer wrote:
 If the chip is faulty, yes.

By ‘chip’ do you mean the ‘transistor’? Sorry for my ignorance but I am not an electronics expert :$ I have also found an image of the A500+ keyboard internals. I found the (red) wire I have to test on this image but cannot identify the transistor. Does anyone have a pointer on where this transistor can be found on the A500+ keyboard?

Regards,
Sim085

[Protek]

sim085 wrote:

rkauer wrote:
 If the chip is faulty, yes.

By ‘chip’ do you mean the ‘transistor’? Sorry for my ignorance but I am not an electronics expert :$ I have also found an image of the A500+ keyboard internals. I found the (red) wire I have to test on this image but cannot identify the transistor. Does anyone have a pointer on where this transistor can be found on the A500+ keyboard?

Regards,
Sim085

The chip contains the transistor. Just look for '74LS27'. :-)

Looking from the picture at Amiga Hardware, it seems that the chips aren't socketed, so soldering is needed. I guess, I'll just swap the whole controller board.

[amigaksi]

>Does anyone have a pointer on where this transistor can be found on the A500+ keyboard?

I think you need to narrow it down to that first before you swap transistors or chips.  First you should connect pin 3 of the keyboard connector to GND (pin 6 of the same connector is GND or shield as someone suggested and Pin 1 is on the left when you look at the motherboard from the front).  If it resets, it's the wire coming from the keyboard or some component on the keyboard.  You still don't have to replace the entire keyboard, as you can simply install your own switch to reset using Pins 3 and 6.  I had the opposite case happen to me where the reset key was always down (zero volts) so amiga would not boot at all.  Simply cutting the wire going to pin 3 made everything work (except the reset).  Eventually, the whole keyboard got replaced with a simulated one, but that may not be an option for you.

[sim085]

Hi again,

Just wanted to thank everyone for all the help given to me so far I will reply here with anything new I find regarding the problem!!

Thanks to everyone again.

Regards,
Sim085

[sim085]

rkauer wrote:
Using a wire jumper (with Amiga turn on), short it to the thin shield somewhere. The Amiga must reboot. If so, you have the reset transistor burned (just change it to another equivalent)

I tested this out the other day and my A500+ did reboot when I short it to the thin shield. Thus means that the reset transistor is burned! Does anyone know from where I can buy an equivalent transistor?

[sim085]

Hi again,

I opened my amiga today and I do not have any chip marked as '74LS27'. However I have one marked as 'HD74LS27P'. Is this the same chip? Also since this is a chip and not just a transistor is it still easy to find?

[rkauer]

sim085 wrote:
Hi again,

I opened my amiga today and I do not have any chip marked as '74LS27'. However I have one marked as 'HD74LS27P'. Is this the same chip? Also since this is a chip and not just a transistor is it still easy to find?

 Yes, HD is the manufacturer "code", 74LS27 is the chip code (a TTL-LS chip) and P means some sort of revision. But prefer to swap the TRANSISTOR before change the (inexpensive) TTL, since it's easier to do.

 The transistor (one of those funny black things with 3 legs under it) can be replaced by a BC547 series. Just notice the BC547 have the pins "backwards" compared with the 2SC1815 (C1815 on the transistor itself). The middle pin have the same function. The probable culprit is branded "Q2" on the keyboard board.

[Protek]

rkauer wrote:
 Yes, HD is the manufacturer "code", 74LS27 is the chip code (a TTL-LS chip) and P means some sort of revision. But prefer to swap the TRANSISTOR before change the (inexpensive) TTL, since it's easier to do.

Yes, there seems to be some actual transistors there. Since chips usually have transistors integrated into them, I drew a wrong conclusion, when you talked about the reset line connected to the pin 8 of 74LS27. :oops:

[sim085]

I think I know for which transistor you mean. So this transistor does not have any specifications? I just ask for a BC547 and they would have even though they where used back in 1991!?

[zipper]

At least BC547A, 547B, 547C listed in a shop quickly glanced.

[sim085]

Thanks for your reply. What I meant is if these Transistors are still called with the same name as back then.

I live in Malta and therefore I was hoping I could buy one of these from a local store rather then order them from another country. To buy them I would need to know the name

I will try to ask for a 'BC547' transistor. If they don't have then I'll try for the others you mentioned if they are the same type.

ps: found this good article on transistors here:
http://www.4p8.com/eric.brasseur/vtranen.html

[weirdami]

(A500+) Ctrl + Amiga + Amiga does not work.

I think the problem is with your (A500 key.

[sim085]

weirdami wrote:

(A500+) Ctrl + Amiga + Amiga does not work.

I think the problem is with your (A500 key.

I tried the keys from workbench and individually they all seem to work. I then used a multimeter to check if current is passing properly from the red wire and it is. I then Using a wire jumper (with Amiga turn on), short it to the thin shield and the Amiga reboot. From the other posts they told me that if this happened then it meant that the transistor burned and that I had to change it to another equivalent.