Moderators: Mug UK, Zorro 2, Greenious, spiny, Moderator Team
troed wrote:Replacing TOS with known good chips is always an easy start. Verify the jumpers are in the correct position for the chips used.
czietz wrote:No, the ROMs from an STF will not work in an STE.
There is not that much you can do without measuring instruments. You could try to carefully remove and reinsert socketed ICs in case the contacts are bad due to corrosion. You could try replacing the power supply (e.g. by one from the STF, they are compatible). Other than that you'll quickly end up in a situation where a multimeter or even an oscilloscope is required, I'm afraid.
Which kind of monitor are you using? Is it some kind of modern LCD / TV that will show you whether a video signal is present? Iirc, right after power-up you should see a 60 Hz color mode.
mlynn1974 wrote:What are the states of the following pins?
HALT: pin 17
BERR (Bus error): pin 22
I am thinking that HALT will be low and BERR may be high.
As mpattonm says it would be wise to check the clock signal first.
mlynn1974 wrote:I would suspect that the ROMs are at fault. I am not familiar with the STs physical ROM chips but I have seen arcade guys on YouTube with hardware to calculate checksums for EPROMs. That would tell you if they are bad or not. If either of them are bad then you should replace them with known working TOS 1.06 or 1.62 ROM Chips as stated.
markjw wrote:...and take a look at the reset circuit to see what it is doing.
markjw wrote:ok, got myself a logic probe - results are:
BERR - HIGH
HALT - LOW
RESET - LOW
mpattonm wrote:markjw wrote:...and take a look at the reset circuit to see what it is doing.
I guess you have already answered your own question:markjw wrote:ok, got myself a logic probe - results are:
BERR - HIGH
HALT - LOW
RESET - LOW
Both RESET and HALT are "active low" signals, meaning your CPU is stuck in reset condition. Have you checked reset switch circuity, as czietz suggested (http://www.atari-forum.com/posting.php?mode=quote&f=15&t=34368&p=356632#pr353396)? Reset pushbutton is very common point of failure.
Once you have that rulled out, I would start removing all socketed chips sharing XRESET line (consult schematic i.e. here: http://www.gossuin.be/images/schemasata ... 600dpi.pdf) one by one to see which one is holding the line down. If it comes down to CPU and its getting VCC and clock all right, your CPU is most likely faulty. That would actually be the best case scenario, as unlike Atari custom silicon, they are dirt cheap and easy to get.
EDIT: I would order replacement CPU in any case, as replacing your stock CPU with HC variant for 2.2USD is always a good idea. Even if the original turns out not to be the root cause of your problem.
https://www.aliexpress.com/item/MC68HC0 ... 86143.html
markjw wrote:EDIT - interesting, 555 @ U104 is getting hot (hadn't noticed that before) - appears to be no output on PIN3 (OUTPUT) and outputs on U210 are low. When the Reset button is pressed I get HIGH on the 555 OUTPUT
Users browsing this forum: No registered users and 3 guests