GAL16V8 as stopgap for dead video ULA

[dominicbeesley]

And or mix ups with the invert jumper vs invert bodge wire

[dominicbeesley]

Sorry. I posted that before I had finished typing.... depending on what version of the video you have you may need jumper S26 in either East, West or you may need the 'bodge wire'. Or you may have the bodge wire and it has fallen off.

Which part number ula do you have?

D

[Danto1]

rev 7, ula ferranti, when I find time I will check what you wrote, thanks

[KGE]

Added DISEN delay circuit and accompanying GAL logic, updated schematic

[1024MAK]

rev 7, ula ferranti, when I find time I will check what you wrote, thanks

No "bodge' wire required and hence the board must not have it fitted.
Link S26 should be fitted as per the service manual, 'West'.

Mark

[dominicbeesley]

I did fmend up with a machine that had a no bodge required ula fitted and S26 fitted and the bodge wire fitted.... that didn't work...I can't remember the exact symptoms but it had me going until I realised the problem... it was of course me that had caused the problem randomly swapping ula's about

[Danto1]

For me it looked like it was working fine at first, but after checking the floppy drive something went wrong. Now only a dash is displayed and no sound when turned on. when entering mode 7, only a line appears, the rest of the modes are ok. I checked everything you wrote, there are ic15 signals, I didn't find anything damaged, I replaced all systems and cleaned the contacts, except the video hive because I have a second BBC, but there is vc2023. can replace the socket in the 6845. I found a damaged 17.7345 MHz quartz, I have already ordered it, but I think it is only for RF. I have an RGB cable.

[1024MAK]

The 17.7345 MHz quartz crystal is only for the PAL colour encoder circuitry, which on a machine from the factory, is only used for the RF/UHF TV output. It does not affect the RGB output or the monochrome composite video output on the BNC socket.

If MODEs 0 to 6 work correctly, then as said above, it does narrow the problem down rather a lot.

It's unlikely to be the 6845, as that is needed for MODEs 0 to 6 as well as MODE 7.

Have you checked IC27, IC36, IC39 and IC40?

Mark

[Danto1]

Unfortunately, I checked ic27, ic36, ic39, ic40 and they are OK on the tester. I think I still need to replace the base in IC2(6845), because the quartz next to it is rusty, although I had previously sprayed the reed switch and cleaned it. It's a pity that I don't have a way to check the ferranti hive.

[Danto1]

Unfortunately, I checked ic27, ic36, ic39, ic40 and they are OK on the tester. I think I still need to replace the base in IC2(6845), because the quartz next to it is rusty, although I had previously sprayed the reed switch and cleaned it. It's a pity that I don't have a way to check the ferranti hive.

[KGE]

Unfortunately, I checked ic27, ic36, ic39, ic40 and they are OK on the tester. I think I still need to replace the base in IC2(6845), because the quartz next to it is rusty, although I had previously sprayed the reed switch and cleaned it. It's a pity that I don't have a way to check the ferranti hive.

It might be wise to start a new thread for your specific problem so others can find it too.

[Danto1]

Yes, you're right, sorry for cluttering up, but I suspect I have to use your diagram, it's a video after all, thanks

[KGE]

Yes, you're right, sorry for cluttering up, but I suspect I have to use your diagram, it's a video after all, thanks

No problem, just giving others the chance to chime in too on your ULA problem

[Danto1]

the ivert signal, I don't know yet where it should be connected to the ULA lens, it is not in the diagram.

[KGE]

the ivert signal, I don't know yet where it should be connected to the ULA lens, it is not in the diagram.

The invert signal is not implemented, if needed you can add it in the logic of GAL1, it has input pins to spare.

[Danto1]

Ok, thanks , but you didn't install the decoupling capacitors.

[Danto1]

And one more question, is this replacement videoul a ferranti 5c094 or can it also be checked as 2023.

[Danto1]

Well, I checked it myself, it doesn't work perfectly, but ok, tested instead of 2023. I designed the PCB somehow, thanks

[Danto1]

But something is wrong, text mode is ok, graphic mode doesn't work. whole screen green or other color. I gave these 4 resistors 0R. Have you tested this latest 74hc74 chip on the original hardware?

[KGE]

But something is wrong, text mode is ok, graphic mode doesn't work. whole screen green or other color. I gave these 4 resistors 0R. Have you tested this latest 74hc74 chip on the original hardware?

0 Ohm might heat up the SRAM chip output buffers when outputting data (most of the time).
Replace them with something like 10k or so. They are just there to keep the unused data lines from floating when writing.

And yes, this picture is from the protoboard with the LS74 in place. Have you connected the set and reset pins? With a LS74 it is not a big deal if these pins are left floating but HC is 'allergic' to that.
Check with an oscilloscope if available to see what is going on.

Text mode (MODE7) is easy as it is generated by the SAA chip, all other modes have to go through the SRAM palette.

[Danto1]

Set and reset are not connected. I'm self-taught in electronics, I don't know much about circuit design, etc. It's one thing to repair it according to the diagra . I suspect that the set to pin 4 and the reset to pin 6 of the 74ls74 system. Or so? because in the diagram it is pin 4 to vcc.

[wiggy]

0 Ohm might heat up the SRAM chip output buffers when outputting data ...

It might also collapse the internal rails of the chip, probably impacting the other outputs and possibly affecting its operation. Or maybe just melting the poor thing.

[Danto1]

resistors changed, ttl 74 changed to LS. I have an oscilloscope where I can measure these signals at the RGB output from SRAM

[Danto1]

RESET connected to vcc according to your diagram, where should SET be connected? . In my BBC Micro II, vc2023 is partially damaged again, it heats up terribly, I installed a large heat sink and the colors are not the same in text mode. I will use this module there, but the graphic mode does not work

[Danto1]

Something is probably wrong with the jed file for gal20v8. No signals at the output to ls175. I programmed several systems and the same thing, I also replaced the memories. I can also send the gerber file to pcb. You can check if the je file is ok, thank you