1040 STF showing occasional rogue pixels

[PhilC]

Sounds like you've either broken a couple of joints or joined some together with the reflow, very easy to do by accident with smd stuff.

Best grab a large magnifier or usb scope by the sounds of things.

Good luck.

[sandord]

Apparently, RAM access has fallen down to 50% of regular ST performance. On the upside, the rogue pixels don't show up anymore. But, I see the occasional flash in the bottom 20% of the screen in Metrocross. It's rather subtile, more like a few lines dim during a single frame. The dimmed area in the picture below is not what I am talking about btw

IMG_20180929_125222.jpg (273.25 KiB) Viewed 3764 times

[sandord]

Sounds like you've either broken a couple of joints or joined some together with the reflow, very easy to do by accident with smd stuff.

Best grab a large magnifier or usb scope by the sounds of things.

Good luck.

I didn't do any SMD soldering, only refreshed legs on the bottom of the PCB. I've checked all of them with a magnifying glass, none appear to be joined or anything. I'm now reflowing anything that looks suspicious.

[sandord]

I saw another bad pixel at the bottom of the screen when running YAART.

So basically, we're now stuck with an ST that still has memory problems and now runs at only 50% memory speed. Yay

[Steve]

I don't understand how this thread is 53 posts long now, as far as I can tell all you needed to do was replace the faulty ram.

[czietz]

Exxos pointed me to this thread. It is correct that YAART does not test the ca. 2.5 kB of screen memory where the status is displayed. It'd increase the program's complexity significantly if it were to test these last bytes of memory with the same coverage as the rest. Yet, I'll think about what I can do to improve YAART in that regard.

I've seen that Exxos pointed you to a program that (specifically?) tests the screen memory -- without any status output. Did that program find any errors?

[sandord]

I don't understand how this thread is 53 posts long now, as far as I can tell all you needed to do was replace the faulty ram.

Well, for one this has been a learning experience for me. Besides that, it's not economical for us to replace the RAM in this machine. Since I'm not capable to replace the j-leaded RAM chips myself (I don't have any SMT soldering experience) we'd have to send it to a repair shop. I could of course fit in an Exxo's solderless memory upgrade kit but that'll set us back for nearly the price of two STs.

Moreover, I'm not yet convinced that 'simply' replacing the RAM will fix the problem. Since I haven't been able to detect any memory problems using 4 different testing utilities, I'd suggest that something else might be going on. As a side node: my friend managed to spot a memory fault in YAART a month or so ago but since I got my hands on this machine, I haven't seen any faults as I mentioned.

Now that the machine seems to run at 50% ram access speed (according to GemBench), I'd first like to know if that could even be the result of faulty RAM or possibly something else in the machine. Running at this lower speed, most memory problems have disappeared but it renders the ST pretty useless due to the now much lower performance.

[sandord]

Exxos pointed me to this thread. It is correct that YAART does not test the ca. 2.5 kB of screen memory where the status is displayed. It'd increase the program's complexity significantly if it were to test these last bytes of memory with the same coverage as the rest. Yet, I'll think about what I can do to improve YAART in that regard.

Thanks for checking this out.

I was just thinking, isn't it an option to relocate the screen memory during the test or even randomly at the beginning of the test, as a transparent (ptagmatic) solution? Or simply cover the last 2.5 kb of the screen as well and clean up the rubbish before displaying the stats as an option? I'm sure you know best how to solve this though.

I've seen that Exxos pointed you to a program that (specifically?) tests the screen memory -- without any status output. Did that program find any errors?

I ran the specific program and it didn't report any errors either.

[exxos]

Exxos pointed me to this thread. It is correct that YAART does not test the ca. 2.5 kB of screen memory where the status is displayed. It'd increase the program's complexity significantly if it were to test these last bytes of memory with the same coverage as the rest. Yet, I'll think about what I can do to improve YAART in that regard.

Maybe just allow the screen to fill with whatever patten its testing, and just pause the text output during that time, and just display the text when not testing screen memory ? We don't need the text to display 100% of the time really.. and testing screem mem is only a few seconds...

[rubber_jonnie]

Apparently, RAM access has fallen down to 50% of regular ST performance. On the upside, the rogue pixels don't show up anymore. But, I see the occasional flash in the bottom 20% of the screen in Metrocross. It's rather subtile, more like a few lines dim during a single frame. The dimmed area in the picture below is not what I am talking about btw


IMG_20180929_125222.jpg

It may not make a difference, but your reference machine is an STE with TOS 2.06 and Blitter enabled, it may be worth looking at the reference you're comparing against just to be doubly sure of your readings.