exxos's Atari, Amiga & retro forum

Just killed Bench6. Appears the machine is pretty solid. :)

:bravo:

Found a issue.. serial failed cart loop back test.. tried with terminal and out works as seen on the diagrom output but it doesn't take input from the terminal. Midi works fine.

@Icky , @exxos I've got a board issue. It looks like rs232 in should go to pin 7 of the MAX238 but its now connected to pin 20 which is an output. I lifted pin 20 out of the socket and connect pin 7 and 20 together on the board and it now works.

derkom wrote: 04 Dec 2019 19:28 Nice work @PaulJ! There go my dreams of competition glory. :lol:

Now that you have a working system, could you do me a favour and check the resistances between video DAC pins 7 and 8, 31 and 32, and 43 and 44 (i.e. three pairs)? I suspect something is up with mine there and would like to compare. Thanks!

EDIT: Oh yeah, and can you tell me how hot your DAC is getting? Mine's hot, right around pain threshold. Wondering if that's normal.

Derkom, do you have a pinout for the STV8438? The PDF I have shows it in a dip case only. Also I'm not sure resistance will tell you much, how about some scope images?

derkom wrote: 04 Dec 2019 19:28 Nice work @PaulJ! There go my dreams of competition glory. :lol:

Now that you have a working system, could you do me a favour and check the resistances between video DAC pins 7 and 8, 31 and 32, and 43 and 44 (i.e. three pairs)? I suspect something is up with mine there and would like to compare. Thanks!

EDIT: Oh yeah, and can you tell me how hot your DAC is getting? Mine's hot, right around pain threshold. Wondering if that's normal.

Found it, looks like one direction is ~5.0 megohm and reversing the meter leads is ~5.4 megohm. Your better off looking at active signals than resistance readings. :D

PaulJ wrote: 05 Dec 2019 03:28 Found it, looks like one direction is ~5.0 megohm and reversing the meter leads is ~5.4 megohm. Your better off looking at active signals than resistance readings. :D

Okay, but there are three pairs of pins, one pair associated with each of R, G, and B, and what I'm actually interested to know is whether they're different. Were your readings ~5 MΩ for all three? This is what I see on my three pairs:

MUX_B0 -> BS : 3.76 M
MUX_G0 -> BS : 55 k
MUX_R0 -> BS : 1.2 M

I agree that looking at signals is a more instructive avenue, but this was just a quick test that made me go "hmmmm".

Here is the datasheet for the QFP version of the DAC: https://www.exdwh.com/data/STV8438CV.pdf

PaulJ wrote: 05 Dec 2019 02:54 @Icky , @exxos I've got a board issue. It looks like rs232 in should go to pin 7 of the MAX238 but its now connected to pin 20 which is an output. I lifted pin 20 out of the socket and connect pin 7 and 20 together on the board and it now works.

Looks like I renamed the pin (where I would have had to delete the line to create a new one) and put it back on the wrong pin :(

derkom wrote: 05 Dec 2019 07:28

PaulJ wrote: 05 Dec 2019 03:28 Found it, looks like one direction is ~5.0 megohm and reversing the meter leads is ~5.4 megohm. Your better off looking at active signals than resistance readings. :D

Okay, but there are three pairs of pins, one pair associated with each of R, G, and B, and what I'm actually interested to know is whether they're different. Were your readings ~5 MΩ for all three? This is what I see on my three pairs:

MUX_B0 -> BS : 3.76 M
MUX_G0 -> BS : 55 k
MUX_R0 -> BS : 1.2 M

I agree that looking at signals is a more instructive avenue, but this was just a quick test that made me go "hmmmm".

Here is the datasheet for the QFP version of the DAC: https://www.exdwh.com/data/STV8438CV.pdf

Well my measurements were all approx. the same. The outlier was 43 & 44 where I got 5.6 and 6.1 megohm. So my measurements all ranged from 5.0 to 6.1 megohm. From my experience this is pretty mush a valueless measurement. It really depends on the ohm meter making a measurement through a semiconductor. The readings are significantly different though so you will have to draw your own conclusion. Like you said you may have fried the chips. Did you use hot air or soldering iron. I used a soldering iron which I'm comfortable with. I've tried hot air and have no faith in my ability to use it. Blowing the small components away or sitting there forever cooking things. I'll stick with a iron and leaded solder. TF did an excellent video on SMT soldering techniques. I don't have the link any longer but if you as him I'm sure he could point you in the right direct. :D

PaulJ wrote: 05 Dec 2019 02:54 @Icky , @exxos I've got a board issue. It looks like rs232 in should go to pin 7 of the MAX238 but its now connected to pin 20 which is an output. I lifted pin 20 out of the socket and connect pin 7 and 20 together on the board and it now works.

I guess that explains why my serial dont work.