7MHz MSX Upgrade - Trouble Shooting

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By Colemu

Hero (535)

Colemu's picture

14-01-2013, 12:03

RetroTechie wrote:

You did read those generic instructions about replacing slow ROM or RAM chips with faster ones if needed, did you Colin? Wink

I replaced these a while back, 27C512 EPROM for ROM's X3 (Atmel I think it was), AS6C4008 SRAM.

Quote:

Oh, last bit: with /SLT30 on a diode input, you should be able to disconnect floppy controller /CS signal from other diode input. In fact I'd recommend that, especially for testing (just try software that doesn't need the floppy after it's loaded, load it @ 3.58 MHz, when loaded switch to 7 MHz, play game & see if machine does anything weird).

Games etc work fine in the machine once they are loaded at 7MHz, as long as they don't need floppy access.

I am currently using the following config:
820 ohm resistor betweem /SLT30 signal and Turbo diode. Also a 820 ohm resistor between Turbo diode and earth (this seems to add some stability). This lasts about 1h 30mins before the system starts to reset whilst loading, the longest I have managed so far.

By Colemu

Hero (535)

Colemu's picture

14-01-2013, 14:11

RetroTechie wrote:

Better yet: replace the ROM with a faster EPROM (eg. ~100 ns part). Unless you have an EPROM programmer yourself & know how to rewire the IC socket, I'd skip that. Also removing that 560 pF capacitor is not an option.

Thanks for this info!

I increased the resistor between /SLT30 signal and diode on Turbo unit to 1.2K ohm (to slow it down further). It has been working for about 2 hours so far. If I have any further problems, I will replace the EPROM with a faster one as you suggest. I know how to do this and have a programmer. Smile

This? http://www.ebay.co.uk/itm/Atmel-AT27C512R-One-Time-Programma...

By RetroTechie

Paragon (1563)

RetroTechie's picture

14-01-2013, 16:59

A 150 ns. EPROM usually works fine @ 7 MHz, 120 ns. is safer, any faster just adds more safety margin. Better stay away from One Time Programmable parts though... Wink (= UV EPROM without the glass window to erase it). If there's already 150 ns. or faster in there, no need to change.

Colemu wrote:

I increased the resistor between /SLT30 signal and diode on Turbo unit to 1.2K ohm (to slow it down further).

Arrgh.. you don't want to slow things down, you want the 7 MHz to respond as quickly as possible to "from 7 back to 3.58 MHz" signals.

I suggest you remove that additional resistor to ground, and try lower values as series resistor. For example 47-100-220-470 Ω. Take lowest that works, and try E12 values around that. When you've found lowest value that works, backpedal 20-50% up (next value or 2 steps up in E12 range). Just do some quick tests for each value (the only thing to test is floppy I/O with 7 MHz on), reserve more time-consuming tests for when you've settled on a value.

FWIW: I don't have a clue why things work at first & then go unstable after an hour or more. This would suggest it juuuussst works, and eg. temperature changes change the situation. Or the 7 MHz board you got is a dud... Evil Things are absolutely stable (including floppy access, and stay that way after hours!) @ 3.58 MHz?

By Colemu

Hero (535)

Colemu's picture

14-01-2013, 18:17

RetroTechie wrote:

A 150 ns. EPROM usually works fine @ 7 MHz, 120 ns. is safer, any faster just adds more safety margin. Better stay away from One Time Programmable parts though... Wink (= UV EPROM without the glass window to erase it). If there's already 150 ns. or faster in there, no need to change.

150 ns, I'm sure that's what's in there (can't check as my SRAM is piggybacking it)

Quote:

Arrgh.. you don't want to slow things down, you want the 7 MHz to respond as quickly as possible to "from 7 back to 3.58 MHz" signals.
I suggest you remove that additional resistor to ground, and try lower values as series resistor. For example 47-100-220-470 Ω. Take lowest that works, and try E12 values around that. When you've found lowest value that works, backpedal 20-50% up (next value or 2 steps up in E12 range). Just do some quick tests for each value (the only thing to test is floppy I/O with 7 MHz on), reserve more time-consuming tests for when you've settled on a value.

I tried the lowest one I had (220 ohm) 1st of all but it was unstable. I'll have to get some lower ones and try them...

Quote:

FWIW: I don't have a clue why things work at first & then go unstable after an hour or more. This would suggest it juuuussst works, and eg. temperature changes change the situation. Or the 7 MHz board you got is a dud... Evil

The computer is stable regardless, only with floppy access does it become unstable sometimes. i.e. when it starts resetting itself, I can load program at 3.58MHz and switch back to 7 and use for as long as I want (as long as no further floppy access is required).

Quote:

Things are absolutely stable (including floppy access, and stay that way after hours!) @ 3.58 MHz?

The computer is stable at all times at 3.58MHz (inc. floppy access), it's been on all day with no problems.

By Colemu

Hero (535)

Colemu's picture

14-01-2013, 20:59

Removed the resistor to ground as advised, only 220 ohm resistor from pin 12 to Diode now.

Doesn't reset at random, boots ok with no disk in drive. Tries to load with disk in drive, but usually blank screen. I think the resistance is too high...

Will order some more resistors and get checking, lowest 1st as you suggest.

I will let you know how I get on Smile

Update: put another 220 ohm in series, and disks now load. Value must be higher than 220 ohm. As above, will play around and let you know the results

By Colemu

Hero (535)

Colemu's picture

17-01-2013, 16:41

I ended up changing the EPROM for another one of the the same type, as the one I had in there did not pass verification.

All works fine now! Big smile

Must have been a dodgy EPROM Tongue

Thanks again all....

By Colemu

Hero (535)

Colemu's picture

23-01-2013, 01:27

I've been using the computer for a while now, and it's working flawlessly. Smile

The only issue I have is with the FM PAC.

It's strange that, in the Cartridge slot that has a constant 3.58MHz (computer running at 7MHz), it works fine on some games, but not others.
I think the difference is:
Games the access the sound chip directly work fine,
Games that use MSX Music bios, don't.

I was just wondering if anyone can explain this? And, can it be fixed? Question

By Colemu

Hero (535)

Colemu's picture

24-01-2013, 15:42

For anyone that's interested, here is a video of the finished modded MSX2 playing the Turbo-R game remake ASO.
Runs slower than on TR and has a few glitches, but I'm amazed it works at all!
here: http://www.youtube.com/watch?v=XtdX5JHvtB4

By Protoman

Resident (44)

Protoman's picture

12-11-2016, 16:37

Hello! Very nice work!! Smile I have a HB-F1XV MSX2+ that I just installed a Z84C0010PEC Z80 10Mhz as well, but I'm having the blank screen/ freezing issue when switching the turbo on after wiring the VDP 3.58Mhz CLK signal directly to pin 30 of the S1985, after lifting the pin from the board trace. I also upgraded the memory to 512K SRAM (I followed the SRAM guide from Tabajara Labs, amazing site!) and I have SRAM pin 22 (/CE) wired to the S1985 pin 53 (/SLT3-3.0)...

You said,

Quote:

At first this didn't work, but I remembered that my SRAM was wired up to CAS. I figured it wouldn't work in DRAM config, do wired my memory up to SLT33. It worked like a dream!

So you wired (/CE) pin 22 of the SRAM to SLT33, which is pin 56 of the S1985? I'm confused about how this would affect the SRAM operation mode since according to the schematic, pin 53 is /SLT3-3.0 and pin 56 is /SLT33... but aren't they both different slot addresses only?

Thank you!!! Big smile

By Protoman

Resident (44)

Protoman's picture

12-11-2016, 17:22

Okay, I just tried switching PIN 22 (/CE) of the SRAM to pin 56 (/SLT33) with no change in system behavior... the MSX2+ still freezes when the turbo is enabled with the S1985 pin 30 connected to the VDP CLK signal. :/ I'm REALLY curious how you got your similar system HB-F1XD to work with the corrected PSG sound! Smile

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