7MHz MSX Upgrade - Trouble Shooting

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By RetroTechie

Paragon (1563)

RetroTechie's picture

11-01-2013, 17:36

Colemu wrote:

Soldered free diode to PIN 12 of IC13 (as this confirmed same point as PIN53 of S1985) but computer won't boot? Question

Wtf.. Question can't think of any ttl-level signal on a diode input that would prevent the computer from booting. At worst it would run @ 3.58 MHz continuous, or switch speeds at a high rate. But if it was running before, it should keep doing so no matter what you hook up to a diode. Maybe that particular diode was fried with soldering? Try another diode input (& solder quicker this time Wink ) just to be sure.

Quote:

I notice that the IC10 TWS2793NL (I'm assuming this is the integrated chip you mentioned?) has a CLK input. Would I be able to just feed this with a constant 3.58MHz signal instead?

No that's the floppy controller. Clock input for that is some multiple (2 or 4 MHz?) of the floppy data transfer rate, don't mess with that. You can hook up the /CS for that chip to a diode input, but in my experience that's not enough for TMS2793-equipped machines. Again: software delays (floppy motor startup, head settling time & other crap like that).

The integrated something I meant is the ROM: BIOS/Basic ROM, subROM, diskROM etc all in one chip (most likely a 128 KB one).

By Colemu

Hero (535)

Colemu's picture

11-01-2013, 18:18

RetroTechie wrote:

You can hook up the /CS for that chip to a diode input, but in my experience that's not enough for TMS2793-equipped machines. Again: software delays (floppy motor startup, head settling time & other crap like that).

Removed from PIN12 of IC13 and hooked up to /CS PIN3 of TMS2793 and works perfect! Big smile
Over the Moon! Thanks mate! Smile2

Re. the keyboard problem I mentioned to you (outside this thread), i.e. keys 01234567 not working. I replaced RB4 resistor array with original value 3.3k, but made no difference.
I wonder if the 1,746,267 times I've removed and replaced the keyboard has work one of the contacts? Question

By Colemu

Hero (535)

Colemu's picture

11-01-2013, 19:19

Update: Whilst switched on I played about with the ribbon cable coming from the keyboard and they started working again. Looks like there is now a break somewhere in the plastic ribbon cable. Not suprising really the amount of times it's been in and out!

Anyway, I packed some wires behind it and they are working. Hope it holds out! (fingers and toes crossed!)

I want to say a HUGE thank you to RetroTechie for getting me through this upgrade, the 512k upgrade, and the V9958 upgrade. I never for a second thought I'd get through one of them, never mind 3! I wouldn't have either if it wasn't for you my friend... Big smile

You should be wearing your underpants on the outside, and maybe a cape too! LOL!

Thanks again for all your help!!!!!!! Hannibal

By Colemu

Hero (535)

Colemu's picture

11-01-2013, 21:09

Well it lasted a while, but then same symptoms.
I guess you were right again, /cas isn't enough.

I'll try PIN12 again using another diode.

My comments still stand, just a tiny bit further to go.........

Update: tried that, boots, but disk access problems... Question
Uploading a video to show you whats happening

Here: http://www.youtube.com/watch?v=TG-Jz25ppDk

By Colemu

Hero (535)

Colemu's picture

12-01-2013, 01:31

Here is a video of free diode on Turbo connected (directly) to PIN53 of S1985

Yes its a clean solder (verified with Multimeter): http://www.youtube.com/watch?v=zq0vdA187Ec

Any ideas would be welcome...

FYI: (taken from enclosed instructions)
Philips VG8230/00 - free diode goes to U41 pin13 (74LS32)
Philips VG8235/00 - free diode goes to U8 pin13 (74LS139)
Philips VG8235/20 - free diode goes to TP10
Philips NMS8245 - free diode goes to TP10
Philips NMS8250 & NMS8255 - free diode goes to IC155 (74LS32) pin2
Philips NMS8280 - free diode goes to IC155 (74LS32) pin2
Sony HB-F700P & HB-F700D - free diode goes to IC16 pin 10 (SN74LS00N, from schematic)
Sony HB-G900P & HB-G900D - free diode goes to IC144 pin9 (SN74LS08N, from schematic)
Sony HB-G900AP - free diode goes to IC133 pin9 (SN74LS08N, from schematic)

Don't know if this helps??

By Colemu

Hero (535)

Colemu's picture

12-01-2013, 14:03

A little more info regarding the Turbo install:
Old Z80 removed and replaced by Turbo assembly (Duh)
Trace cut so that only the NTSC decoder (HIC-1) receives the 3.58MHz signal from VDP
Trace cut to remove S1985 from Turbo circuit (pin30) and connected to VDP 3.58MHz signal
Trace cut to remove cartridge 1 from Turbo circuit (pin42) and connected to VDP 3.58MHz signal

All other parts recieving timing from the Turbo circuit.

Currently, one of the free diodes, on the Turbo assembly, is connected (directly) to the /CS pin of TMS2793 as this is the most stable config at the moment. Lasts about 30 mins before Floppy Disk Access problems re-emerge. As all the other MoBo instructions state connections to logic gates (I think), maybe this also needs to be that case with this board? Question

7MHz Works forever if either working from Cartridge or game loaded to memory and no further disk access is necessary.

Update: Added a schottky diode to /CS pin of TMS2793 to add a slight delay, seems to have done the trick! Big smile
Will use the machine today and post resuts for anyone who's interested....

By Colemu

Hero (535)

Colemu's picture

13-01-2013, 00:45

Nope, lasted quite a while but same again.
However!

RetroTechie wrote:

I can't tell from the schematic, but OpenMSX config for this machine says diskROM is in slot 3-0? Don't trust me on that, check using MSXMEM for example! If so, /SLT30 signal can be picked up from S1985 (pin 53, not easy to solder to for beginners), IC13 (74LS32) pin 12, or solder somewhere to the circuit trace in between.

I figured out why this was causing the system to have problems booting etc, it was because the voltage coming from PIN 12 of 74LS32 (i.e. /SLT30 signal) was too high.
I added a 820 ohm resistor between this PIN and a free diode on the Turbo PCB, and what do you know, it works!! I've been running down the street naked I'm sooo pleased Running Naked in a Field of Flowers

Got there in the end, thanks for the advice/guidance it was correct. Just needed a little fiddling, which only I can do since I have the machine oO

I refer back to my previous comments, f*c*ing hero man!! Hannibal
http://www.youtube.com/watch?v=9rvd5F6_pdE (video of working Drive & 7MHz Turbo)

By syn

Prophet (2061)

syn's picture

13-01-2013, 00:45

Wait.. you have a 7mhz MSX2+ with music playing at normal speed and pitch? (its been 20 years since I played quinpl so I cant really tell by that video you posted).

Im kinda noob at msx hardware but I dont think I have evern seen this before?

By Colemu

Hero (535)

Colemu's picture

13-01-2013, 00:57

Hi Syn,

it is a MSX2 that I upgraded to MSX2+ by changing the VDP and Basic ROM, then added 512k RAM for good measure.
As I changed the first Cartridge port to output a constant 3.58MHz signal (see earlier in this thread), my MSX Music & SCC music (and any other music cartridge you care to use) plays at the correct speed and pitch at 7MHz. I also hooked up the internal PSG to 3.58MHz so that that also plays at the correct speed & pitch at 7MHz.

Quinpl, great little game, and yes the music plays just as it would at standard speed Cool

By Daemos

Paragon (1951)

Daemos's picture

13-01-2013, 01:04

Quote:

I added a 820 ohm resistor between this PIN and a free diode on the Turbo PCB, and what do you know, it works!! I've been running down the street naked I'm sooo pleased

Never lower voltage by just putting a resistor inbetween. You are creating a lot of current in that resistor right now.
Always make a voltage divider of some kind.

like 5V-------\/\/\/\/----------2,5V
                2 ohm     |
                            |
                          1 ohm
                            |
                         -----
                           --
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