Rolling Screen running RomWBW

[Larry Critchfield]

I am looking for some help Please !!!. I pulled out my box of RC2014 blank boards from around 2018 and started building this puzzle about three weeks ago. I had bought a set of Scott Bakers white CPU, SIO/2 and 512kRamRom boards plus others from different makers. I have his modified RomWBW V2.7.1 files that have a 512KB smb_sio.rom. I burned the rom and it does not work as expected. It Id's itself, lists my sio 1 and 2 , 2 ram discs and 2 rom discs then repeats over and over and over. I know it is supposed to be asking to load or select something so I think the problem is software.

I built a new rom from Scotts files with the same results.
I do not have the skills to look at the binary and see where it goes bad. I think it jumps to the next screen write but gets bounced right back to the start. And I can not prove it, I have Small Computer Monitor and basic running using different ram and rom boards but that does not help me.  

On the 512k RamRom board I have replaced every chip on the board. I have installed some of the chips into my Micro8088 and all is good.
I ohmed the pull down resistors ( all 10k on this board ) and checked the paths from backplane to the chips. All check good.

I looked at the newest RomWBW and there is no SMB board to choose from when building the rom ? What do other people with this 512k RamRom board use?
I think Scotts only changes were locations for some of his extra cards which I don't have so some other roms should work (says me but so far they do not )  I did not log the roms that I did try.
So I have a 40 pin backplane with 8 sockets fed 5 volt. ( I tried both a switcher and a transformer based power supply )  , Z80 cpu board, SIO/2 board and the 512kRamRom to run RomWBW.
 
I greatly appreciate any help. I have been searching for an answer to this issue with no luck.

[Willy De la Court]

How are you powering the setup?

This really looks like a reset problem due to power dipping below a certain threshold and generating a reset signal.is there a DS1233 on the power board.bus?

[Larry Critchfield]

CPU board has a surface mount power monitor reset device 4 leg. I can not think of the number. Expensive little thing. I thought of the reset line and talked myself out of that because of the board running basic in a printing loop for an hour with the other rom and ram board. I will put my scope on the reset and see how it looks. I will report back, wouldn't that be easy to fix !!  

[Steve Cousins]

Willy makes a good point. If your system has a voltage supervisor (eg. DS1233) it could be tripping. Try removing one of the optional modules to reduce the power consumption and see if that fixes it. The floppy disk interface would be a good candidate.

Another approach is to remove all optional modules so you have a minimal system. If it then runs okay, add one module and try again, until you find the problem module.

Steve

[Larry Critchfield]

Willy, Steve. I am using a 5 volt switcher plugged into the backplane. The reset makes sense. It is a MAX811.  I only have 3 cards in the back plane. cpu, sio and 512k ramrom. Reset is solid, I pulled the ramrom and installed 32k ram and 32k rom boards . I took an image of Small Computer Monitor running on the new rom. I took a pic of the reset and the 7.37mhz clock at 1 volt per div. I looked at the mreq, rd and tx, each pulsing in time with the repeated start. I think I should see a ripple in the reset line.

I want to see what you think. I am running it now with a 5 volt transformer regulated power supply, Same thing

Can I run anything on the RamRom board without bank switching like SMC ?? If the 512k RamRom was not switching banks would it default to 32k rom at 32k ram ? I somehow don't think so. Be too easy

[Larry Critchfield]

System Clock Image - 1 volt per division

Reset Image  - 1 volt per division

Small Computer Monitor Running with different boards

[Larry Critchfield]

I removed the Max811, added 2.2K pullup on Reset line.

Same PROBLEM. So it's either the 512KRamRom board or its in a software loop.

This board uses the same address as Spencer's.

I have tried a few different roms but only one shows activity. Prints a C on the screen after every reset.

Hit enter and it prints the same ascii character to the screen over and over.  

Any ideas ?

[Willy De la Court]

Short on one of the addresslines/datalines on the ramrom board check all solder joins

[Larry Critchfield]

Thank you, I am on it !! These circuit boards with the silk covering all but the solder pads look nice but are difficult to visually inspect/ trace.

Via's so small It's hard to believe it is possible. I must lay one out with these wire sizes. Routing should be less difficult than it used to be..  

[Larry Critchfield]

512kRomRam Board FIXED !!!!!

It was A16 on the Rom chip. A16 is ONE (1) of SEVEN (7) Banking Bits created from the Data bus. D2 = M[A16] coming from the 74HCT670 chip pulled low by a 10k resistor. Problem was the Socket itself. That Rom had been pulled many times and the pin lost its shape. Not a quality socket to start with. Reshaped the pin to provide pressure again. I will replace it as soon as I can find my new small tip for the desoldering gun. Put it somewhere so I wouldn't lose it.

Thank you Willy and Steve for your help. I was banging my head on the desk.
Now to get Steve's SCM slipped in there !!

Larry

[Willy De la Court]

Very nice it is still happening to me with some solder joints so usually I check them thoroughly.

Have fun with the rest of the build.