Space firebird boot blank screen

[Lurch666]

Puzzling about your rams.

Even if they are too slow they should show some output shouldn't they?

Floating outputs are either bad chips or maybe the chip select is high?

My video board is working as far as the stars appearing if I plug in the sound board so I know sync and RGB output is good.

As I stated earlier the video signal isn't making it past the SN74198 chips because pin 1 and pin 23 are not showing any activity.

If I ground pin 8 of 2B on the video board I get the graphics I showed on the video in my earlier post and pin 23 of the SN74198 becomes active.

So I'm trying to figure out why those pins are normally inactive on my boardset.

 

[Lurch666]

Just checked the prom at 4I and pin 4 keeps coming up as unconnected in my pinmaster48.

I have some equivalent 74s287 but have now discovered that my pinmaster won't write these so I'm offering them in the free stuff section for anyone who has a compatible programmer.

Have ordered some other proms that my programmer can hopefully manage so will wait for them to arrive and see if a good prom at 4I fixes anything.

 

[Lurch666]

New 4I prom arrived today from yorkshire_spam-thanks again dude.

Unfortunately it's made no difference but it's another fault eliminated.

Next I'm going with patziks suggestion it could be slow ram.

I've ordered some AM93422PC ram in the hope this will cause something to appear on my screen without me having to ground bits of the PCB.

 

[Lurch666]

AM93422PC ram turned up today and.....

No difference.

Exactly the same and I even get the same display if I ground pin 8 of 2B and I thought with better memory the display would be improved but nothing.

Getting frustrated now and it's beginning to look like a shotgun since I've replaced so many chips.

Might as well go around the rest of the video board with the slice and change any chips that look even slightly off.

Going to get this damn thing working even if it kills me (or a least drives me to drink which is a very short journey for me anyway

).

 

[Ronnie Dent]

The ram and rom sockets are not too clever on these boards! I was talking to another clever member regards putting all the game code on one larger rom but not ventured there yet.

 

[patzik]

sorry I wasn’t clear on the 5101’s. If I put these in the board I do get graphics, but they are flaky, so this is why I am thinking the ram is too slow. Where did you find the 93422’s if I may ask? Still need to find some replacements for my 2 boards.

 

[RaveN]

As Ronnie Dent mentions, Space Firebird and DK 3-layer pcbs (and maybe others) have really poor sockets. Space Firebird has quite a few ICs requiring -5v (some RAMs and a 2708 from memory), and when people use a more modern SMPS (that ramps up the 5/12v quicker than the -5v) it can destroy those ICs, something to remain aware of.

Are you now able to read in the entire z80 rom successfully, or is it still failing on the last eprom?

 

[Lurch666]

I don't have -5V connected on my firebird.

It's a bootleg and follows a phoenix pinout where there's no -5V

 

[jonhughes]

Glen

It requires -5v to run

There should be a brown wire on the cpu board parts side seventh pin from the top if the edge connector is on the right. Looks like four ground pins all connected would be pins one to four.jonhughes2021-01-29 19:11:00

 

[Lurch666]

If that's what been causing my problems I'm gonna be facepalming soooooo hard!

Will have to follow the -5V from the 2708 on the soundboard to see where on the edge connector I need the -5V.

Will have to wait till tomorrow though as I've been driven to drink tonight and don't fancy screwing it up if I get it wrong

 

[jonhughes]

I will get you pictures if the brown wire isn’t there. I was scratching my head wondering why you were not getting any where with it because as far as I could remember it was only the graphics board that was faulty.

 

[Lurch666]

Since you told me about the brown wire I didn't need to trace the -5V so just added the -5V but still no change.

Bit of a head scratcher this one.

 

[Lurch666]

Just had another look through the schematics and can't see any ram that requires -5V so I'm assuming it's just the 2708 that needs it.

 

[Lurch666]

Found out today that running it with 4F removed from the video board causes lines of graphics to appear.

How can removing a chip make something appear??

 

[Lurch666]

After my last post I was looking at the schematics (for the 100000
time...) and noticed 4F fed an addresse into 6H and 6G so decided to
check them out again in case I had missed something but they appeared to
be ok.

When I checked pin 13 I got a simple waveform.

This
is the write enable and had noticed this before but hadn't investigated
it but now thinking about it most write enables are toggling more or
less at none linier intervals so that got me thinking.

Checking the LS00 at 2C pin 9 had the same simple waveform but pin 10 was stuck high.

Now I'm pretty sure I had checked the LS74 3E before with my slice
but I must have been mistaken because now it was showing errors on pin 5
and 6.

Swapped it out and......

I FINALLY HAVE GRAPHICS!!!!!!

Still very glitchy so I tried removing the AM93422PC chips and putting in the ones I had before and got much better results:

Still not quite right but much better and it's nice to finally have a breakthrough.

Gonna celebrate with beer.

@patzik:Looks like the 93422 chips weren't up to scratch.Do you still want the link?

Lurch6662021-01-30 16:41:47

 

[Lurch666]

Swapped out the 2114 chips on the CPU board to see if that would let the game run at something more than 4.7V but it's made no difference.

I'm guessing now the graphics could be messed up not because of bad or slow memory but because it just doesn't have enough voltage to run properly but until I can figure out what's causing the code to not run if the voltage is over 4.7V I won't be able to test my theory.

 

[yorkshire_spam]

Awesome progress Lurch - nice one!

 

[Lurch666]

Finally sorted.

We knew that It's very picky about the 8 ram chips on the video board and after trying lots of alternative found these on ebay:

Ebay item number 320528512353 (couldn't get a link working).

They came from America as the five I already had came from a European country that thanks to brexit won't ship to the U.K. any more but they should be fine for you patzic.

All the alternative types (5101,93L422 etc) just weren't fast enough and caused graphic glitches.

Lurch6662021-03-11 09:38:26

 

[patzik]

Great to hear, you found the issue. Yes I noticed this board is really sensitive about what ram is used. i looked at the ebay item and $3 per ic plus $16 shipping, and taxes and import fees from the us just makes it not economical I think. Where in europe did you find them? I see some 350ns ones on eBay from Bulgaria, do you mean those?patzik2021-03-11 19:14:43

 

[Lurch666]

ebay item number:303910778998

These are the ones that won't ship to the U.K. but hopefully you will be OK.

I misread your location and thought you were in Harlem,NY so I was thinking you were American-my bad.