STE V1 32Mhz booster - hoping to get some ideas on this..

[oraclejedi]

Hey all,

Hope this is right place to ask for some help.

I have a 520STE. UK Spec. The board is stamped CA4003290 but then just "REV". Not A, or B or whatever.

It has an internal blitter. U405 is a TI SN74F257N.

I put the dual TOS mod in and that worked great.

I then added the 2016 revision of the Rev 1 STE 32Mhz booster following the @rubber_jonnie guide, except I socketed my install in a similar fashion to tt_fh's install.

The STE starts up no problem in either TOS. It can read and write floppy disks and the Ultra Satan. When in 32Mhz mode Gembench reports speed pretty much exactly as expected.

But the screen starts to wobble. A little at first and then more violently. And as time progresses, the vertical sync starts to go. This was the same in 32Mhz mode and 8Mhz mode.

I removed the accelerator and put the original CPU back in. The system was rock solid. No problems.

I then put the accelerator back in again, and this time soldered it, removing the socket. Same problem as before. The screen wobbles.

I have tried various lengths/routes/guages of 32Mhz wire and even though some seemed to help at first, pretty soon the screen starts wobbling again.

Some more notes:

This is a 2016 dated booster. There is no C1 or R1 on the board as shown here: https://www.exxosforum.co.uk/forum/viewt ... 514#p41514

The SIL resistor packs are still present on the motherboard.

I have tested different video cables and monitors. No difference. I have also tried composite output. Same problem.

I started with an Exxos PSU but have since switched to a re-purposed Falcon PSU. This change made no difference.

The machine is UK spec but I am in Seattle. I have 110V PSUs. I have tried using the 50hz/60hz switcher but the problem is exhibited in all scenarios.

I have tried different RAM. The original 1MB of RAM exhibited all manner of issues. The current 2MB was borrowed from another STE and seems fine. All RAM tests pass, and the image is not exhibiting the types of problems seen with parity RAM.

The video upgrade was not done. The machine has never exhibited ghosting and doesn't now. The problem is image stability.

I am considering tf_hh's idea of replacing the with a 74AHCT257, but the wobble is not related to IO operations. It does seem to get worse with time (heat?).

Has anyone got any ideas on what to try next? I have been focusing on the 32Mhz wire to U405 but why would that cause issues in 8Mhz mode? Would replacing U405 be the logical next step?

Would appreciate some expert help if anyone has ideas....

Thanks!

Graham

[Icky]

The first question I would ask is have you done all the mandatory fixes to your STE.

https://www.exxosforum.co.uk/forum/viewt ... =17&t=1585

[oraclejedi]

Thanks for the link to that list.

Looking through:

1 & 2 are done.

3 & 4 address issues with the floppy. no issues with the floppy here.

5 - the CPU was supplied in the 32Mhz kit.

6 & 7 are Falcon specific.

8 - no ghosting but it is an image stability issue.

9 - sounds the closest to the issue experienced. I am thinking a full recap of everything on the STE might be the next logical step.

10 - my floppy is clean. honest.

11 - reset circuit seems to be working as expected

12 - bus resistors. omg those SIL packs are now underneath a soldered in accelerator board. maybe step 1 here is to try to remove the accelerator, and if it survives removal put the socket back in. none of the sample motherboards is an STE with internal blitter but I expect the external blitter example is pretty close. it might need some experimentation to see if such a change helps or hurts.

thanks again.

[Icky]

12 - bus resistors. omg those SIL packs are now underneath a soldered in accelerator board. maybe step 1 here is to try to remove the accelerator, and if it survives removal put the socket back in. none of the sample motherboards is an STE with internal blitter but I expect the external blitter example is pretty close. it might need some experimentation to see if such a change helps or hurts.

You could put some SIL resistors in parallel on the underside of the board that would be a simple fix.

If you have 10K SILs then placing a 2K7 in parallel would give you around 2K1
If you have 4K7 SILs then placing another set of 4K7 in parallel would give you around 2K3

I have done this in the past to save desoldering and soldering on these old boards.

[rubber_jonnie]

12 - bus resistors. omg those SIL packs are now underneath a soldered in accelerator board. maybe step 1 here is to try to remove the accelerator, and if it survives removal put the socket back in. none of the sample motherboards is an STE with internal blitter but I expect the external blitter example is pretty close. it might need some experimentation to see if such a change helps or hurts.

You could put some SIL resistors in parallel on the underside of the board that would be a simple fix.

If you have 10K SILs then placing a 2K7 in parallel would give you around 2K1
If you have 4K7 SILs then placing another set of 4K7 in parallel would give you around 2K3

I have done this in the past to save desoldering and soldering on these old boards.

+2 for this.

[Badwolf]

Just double check your booster doesn't already have parallel pull-ups on it. From the image on the webstore I'd suggest it does:



A simple multimeter resistance check from one of the address or data lines (say D4 at pin 1 [where the dot is] to make it simple) to the 5V rail should do the trick.

BW

[rubber_jonnie]

Just been discussing this issue, can you check to see if you have 2.2K SILs on the booster, they should be marked 222.

Check the Addendum here for more information: https://www.exxosforum.co.uk/forum/viewt ... 2GU#p50402

If you do have the 222 SILs on the booster, then the mainboard SILs can just be removed. You can wiggle them until the break off.

[Icky]

Also @oraclejedi a picture of your board and booster would greatly help us to see any other areas and your progress.

[oraclejedi]

Thanks for the insights everyone,

Here are a couple of pics of the accelerator in the machine. There are SIL resistor packs on the accelerator board itself. If I am understanding things right, this means I should now remove the SIL packs from the motherboard.(P101 thru P105 - leave P100 in place).

20220330_102130.jpg

20220330_102126.jpg

[rubber_jonnie]

You need to check the booster SIL packs are 2.2k before you do anything.