Various tweaks and fixes from video ghosting to audio fixes etc.
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Post by exxos » Thu Jan 31, 2019 4:13 pm

I opened up this thread to list mostly mandatory fixes. While some may or may not agree with these fixes, I personally are classing them as mandatory and you heed my warnings for this! So if you want to keep your machines in tiptop condition with all the currently known fixes and patches, then please take note of all below!

1) All machines - PSU needs recapping.
There is enough evidence over the years to show this should now be mandatory for all machines. Not only do some STE machines failed to boot with 4MB RAM in them because of aged power supplies, the faults can be even worse where voltage spikes can kill machines like Falcons. Looks after your PSU!

2) STE - Parity SIMMS - do not use them!
There has been undeniable proof that some parity simms are not stable in STE machines in particular when the power supply is failing or a accelerator is used. While people may not generally have issues on a stock machine this does not mean there are not issues. So do not use parity simms in any circumstances unless you remove the parity chip from them.

3) STE ,STFM,MEGA ST, (likely other machines effected) DMA Pull up on databus needed.
As people know I have invested best amounts of time to investigating DMA issues. While this is a huge complex topic with various faults, I am passing it mandatory to add a 10K pull up network to the DMA databus. This will solve, and even prevent, future issues with hard drives and floppy drives.

4) STE ,STFM,MEGA ST, (likely other machines effected) 1772 PULL UPS.
The 1772 Has a set of inverters on its output which connect the floppy drive. The original Atari drives had internal pull-up resistors however, other compatible drives such as the MPF920 (and possibly others) do not have the resistors and should be fitted to the Atari directly.

5) STE - Change the CPU for HC type to fix DMA issues.
Changing the STE to a HC type will help solve a lot of DMA related issues. In general write issues with ultrasatan or other hard drives. These are a lot cheaper than replacing the DMA chip itself with a 001 (or "good DMA") which are rather expensive and are generally not in sockets.

6) Falcon - buffer patch.
Adding the clock buffer patch will solve stability issues with the Falcon. It is possible further fixes may be required relating to this topic.
http://www.exxoshost.co.uk/atari/last/f ... /index.htm

7) Falcon - Bulk capacitance.
Changing the 4700uF capacitor one of my capacity kits has been known to solve some SDMA audio related issues. Not only that, my capacity kit will help eliminate voltage spikes coming from the power supply is generally kill the Videl first.

8) STE - Video Ghosting FIx.
The STE and indeed MSTE, suffer from a ghosting problem in the video. Luckily I found a really simple fix this.
http://www.exxoshost.co.uk/atari/last/V ... /index.htm

9) STFM video sync problem
These machines seem to suffer from the video going out of sync intermittently or constantly. Some fixes for this are listed below which generally involve recapping the video circuit.
http://www.exxoshost.co.uk/atari/last/S ... /index.htm

10) All machines - clean your floppy drive!
Such a simple thing and is really done. Of course with floppy head cleaner kits being hard to find or stupid prices, we can easily clean the heads with a little bit of IPA. This will solve a lot of issues reading from floppies.
http://www.exxoshost.co.uk/atari/last/f ... /index.htm

11) ST/F/M/E - Reset fix
Reset circuit is malfunctioning due to bad design and 30 year old bad caps. Machines fail to reset on power up and often need the reset button to be pressed to start the machine.

12) ST/F/M/E - Bus resistors
Bus resistors can cause all sorts of random issues. Plugging in a cartridge can make the machine unstable, changing the brand of the CPU or ROM's can cause various malfunctions. The bus resistors need to be changed for 2.2K to resolve the issues. Most STF/M machines had 10K resistors on the address and databus, these should be replaced with 2.2K. Similar with STE where early machines had 10K and some mixed 4.7K. These need to be replaced with 2.2K.
More information will follow in due time.

A lot of parts can be obtained from my webstore.
4MB STFM 1.44 FD- VELOCE+ 020 STE - 4MB STE 32MHz - STFM 16MHz - STM - MEGA ST - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - HxC - CosmosEx - Ultrasatan - various clutter

https://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
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Post by tzok » Sat Feb 09, 2019 3:13 pm

a.d. 4) Gotek units have internal 1k pull-ups on shugart bus, so no need to make this mod for them.

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