Atari 600xl green and beige screen

[The Mr. Video]

I looked for Red/brown screen in my docs. It said the following:

U2 thru U5, U18, U19, U28, U30. and I would guess Antic or GTIA U7 and U17.

All those mean swapping chips with known good ones.

 

U2 Decoder ; 74LS138

U3 Memory manager

U4 OS ROM

U5 BAS ROM

U18 CO17097

U19 CO61850

U28 Latch 74LS37S

U30 And/Or inverter 74LS51

 

That's not much help, but what I researched about it.

You could take out the BAS ROM and see if you still get the red/brown screen.

It would boot to a blue screen.

I'd start with the OS ROM, Antic and GTIA.

 

If you have socketed chips, that would help a lot.

 

I just tried it, taking the BAS out of a good board. It boots to the self test like you said.

Um...I said it didn't boot to the self test screen.

[russg]

Um...I said it didn't boot to the self test screen.

OK, I'd start with the OS ROM chip if you could. You need a working board to

test from. Which you don't probably have. So, I guess you're sorta stuck.

[The Mr. Video]

Ok so my new power supply came in and now when I turn the computer on I get a white screen even if a cartridge is connected.

[+mytek]

Ok so my new power supply came in and now when I turn the computer on I get a white screen even if a cartridge is connected.

 

Sounds very similar to some of initial boot-up problems we were seeing in the XEL project. In our case it came down to the reset circuit not keeping the CPU in a reset condition long enough to get past any instabilities in the power circuits such as capacitors charging up. The 600XL has a circuit that does this power-up momentary sustained reset just for that purpose. It consists of an inverter IC (U14) and a diode (CR3), resistor (R44), and capacitor (C44). C44 would be a likely culprit since it's an electrolytic capacitor which could have dried up. It's value is 47uf, and probably anything of this value (or even a bit larger) rated for 16 VDC or higher would work.

 

In case you are interested, the circuit works by charging up the capacitor via a 56 K resistor (R44) connected to the 5 VDC power bus, until it reaches a point where the 74LS14 inverter IC's gate input sees a high enough voltage to switch from a logic '1' to a logic '0' on it's output, which is sent through another inverter gate (in order to get the correct logic state required) connected to the CPU's Reset input. The charging of the capacitor takes a small amount of time, so this holds the CPU in Reset during this time (Reset initially will = 0 VDC). The diode is reverse connected across the 56 K resistor so that when power is removed from the bus (power switch OFF) it allows the 47uf capacitor to drain, thus getting it ready for the next power-up cycle (power switch ON).

 

- Michael

Edited June 3, 2017 by mytekcontrols

[The Mr. Video]

Sounds very similar to some of initial boot-up problems we were seeing in the XEL project. In our case it came down to the reset circuit not keeping the CPU in a reset condition long enough to get past any instabilities in the power circuits such as capacitors charging up. The 600XL has a circuit that does this power-up momentary sustained reset just for that purpose. It consists of an inverter IC (U14) and a diode (CR3), resistor (R44), and capacitor (C44). C44 would be a likely culprit since it's an electrolytic capacitor which could have dried up. It's value is 47uf, and probably anything of this value (or even a bit larger) rated for 16 VDC or higher would work.

 

In case you are interested, the circuit works by charging up the capacitor via a 56 K resistor (R44) connected to the 5 VDC power bus, until it reaches a point where the 74LS14 inverter IC's gate input sees a high enough voltage to switch from a logic '1' to a logic '0' on it's output, which is sent through another inverter gate (in order to get the correct logic state required) connected to the CPU's Reset input. The charging of the capacitor takes a small amount of time, so this holds the CPU in Reset during this time (Reset initially will = 0 VDC). The diode is reverse connected across the 56 K resistor so that when power is removed from the bus (power switch OFF) it allows the 47uf capacitor to drain, thus getting it ready for the next power-up cycle (power switch ON).

 

- Michael

Ah, gotcha. I'll be sure to give that a try later.

[The Mr. Video]

Um, where is C44?

[+Stephen]

Um, where is C44?

Give me a few moments - I am trying to stitch together the silkscreen diagram from the FSM for you.

[The Mr. Video]

Update: I decided to feel the chips again, this time I left the computer on a little more than last time, and I noticed that some of the chips are getting hot. The chips circled in the picture are the ones getting hot.

[+DrVenkman]

The big ones are GTIA, ANTIC, thr 6502C cpu, and POKEY. The little one is the MMU chip. They all get warm on most systems, the MMU, 6502 and GTIA especially.

 

Did you ever check the reset circuit capacitor mentioned above?

[The Mr. Video]

The big ones are GTIA, ANTIC, thr 6502C cpu, and POKEY. The little one is the MMU chip. They all get warm on most systems, the MMU, 6502 and GTIA especially.

Did you ever check the reset circuit capacitor mentioned above?

The Capacitor for that just came in today, will replace the old one later.

[The Mr. Video]

Sounds very similar to some of initial boot-up problems we were seeing in the XEL project. In our case it came down to the reset circuit not keeping the CPU in a reset condition long enough to get past any instabilities in the power circuits such as capacitors charging up. The 600XL has a circuit that does this power-up momentary sustained reset just for that purpose. It consists of an inverter IC (U14) and a diode (CR3), resistor (R44), and capacitor (C44). C44 would be a likely culprit since it's an electrolytic capacitor which could have dried up. It's value is 47uf, and probably anything of this value (or even a bit larger) rated for 16 VDC or higher would work.

 

In case you are interested, the circuit works by charging up the capacitor via a 56 K resistor (R44) connected to the 5 VDC power bus, until it reaches a point where the 74LS14 inverter IC's gate input sees a high enough voltage to switch from a logic '1' to a logic '0' on it's output, which is sent through another inverter gate (in order to get the correct logic state required) connected to the CPU's Reset input. The charging of the capacitor takes a small amount of time, so this holds the CPU in Reset during this time (Reset initially will = 0 VDC). The diode is reverse connected across the 56 K resistor so that when power is removed from the bus (power switch OFF) it allows the 47uf capacitor to drain, thus getting it ready for the next power-up cycle (power switch ON).

 

- Michael

I noticed that the capacitor on the board is rated 10 volts. And the on I bought is rated 16 volts. Is this ok?

[+DrVenkman]

I noticed that the capacitor on the board is rated 10 volts. And the on I bought is rated 16 volts. Is this ok?

 

Absolutely fine. Voltage rating on the cap is just the maximum it is rated to handle. 16V is fine.

 

That said, the capacitor installed might not be bad. Did you actually measure the voltage rise on the positive side? If it gets to about 4.7 - 5 V, it's probably fine.

[+mytek]

 

Absolutely fine. Voltage rating on the cap is just the maximum it is rated to handle. 16V is fine.

 

Agreed. I should have said 10V or higher, since that is a 5V regulated circuit.

 

- Michael

[The Mr. Video]

Ok so I replaced the capacitor and it still boots to a white screen even if I hold down the option button.

[The Mr. Video]

Update: After installing the 64K mod, it either boots to a white screen or a purple screen.

[+DrVenkman]

Ok so I replaced the capacitor and it still boots to a white screen even if I hold down the option button.

 

 

Update: After installing the 64K mod, it either boots to a white screen or a purple screen.

 

Did you ever get the stock 16K machine to boot? If not, why did you do a 64K upgrade? You need to figure out why that machine isn't working before you mod it further. Otherwise you're probably just wasting time.

[The Mr. Video]

Update:Just got me a working 600XL mother board off Ebay, so when it gets delivered, I'll be able to start swapping chips.

[The Mr. Video]

Update:I got it to work! I think there was something wrong with the Sally chip, but now I have another problem, the keyvoard is broken. sometimes it just doesn't do anything, other times the A key sticks. The only thing that works all the time are the side-silver keys, I'm wondering if the connector is broken.

Edit:I don't think the help key works either.

Edited July 13, 2017 by The Mr. Video