HB-F9S v9938 partially dead?

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Van Daemos

Paragon (1952)

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02-01-2016, 00:07

Quote:

I've tryed CHKSPD.COM on blueMSX and it reports 3.57 mhz. Is that the correct CPU freq?

That is the normal CPU frequency for MSX

Van blackmsx

Expert (77)

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02-01-2016, 00:29

So then the measuring program should be accurate enough...

Now I need to see what is making my machine to run at 4.05mhz. Any ideas?

Perhaps should I open a new topic?

Van Grauw

Ascended (10064)

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02-01-2016, 00:55

I think a malfunctioning M1 wait signal as was suggested earlier sounds like a probable cause for such a difference. From the perspective of a speed test running on the CPU, absence of the M1 wait will make it appear faster, by something around 10% sounds about right, depending on the test.

Due to this improved speed, it would access the VDP too fast causing graphics corruption, especially in screen mode 0. Try changing to screen 1 (twice) and see if the issues disappear (it accepts faster access speed), I think that would be a good test to confirm that CPU speed is the issue.

[Edit: Also, insert a game cartridge and see if the music plays at a higher pitch than usual, by a couple of semitones. Compare with Youtube. If it doesn’t, the crystal itself is operating at the correct frequency.]

Another theoretical possibility would be a crystal malfunction I guess, but although I’m not really a hardware type of person who would know about this, I don’t think a crystal would malfunction in a way that makes it run faster? I’ve never heard of such a thing at least. It seems more likely that it would just stop working.

No need for a new topic, I don’t think…

Van blackmsx

Expert (77)

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02-01-2016, 01:35

Grauw wrote:

Due to this improved speed, it would access the VDP too fast causing graphics corruption, especially in screen mode 0. Try changing to screen 1 (twice) and see if the issues disappear (it accepts faster access speed), I think that would be a good test to confirm that CPU speed is the issue.

[Edit: Also, insert a game cartridge and see if the music plays at a higher pitch than usual, by a couple of semitones. Compare with Youtube. If it doesn’t, the crystal itself is operating at the correct frequency.]

Yes, as I said before screen mode 1 works fine, so all points to the wrong CPU speed.

XTAL speed is reported at 21.48 which is the same as in BlueMSX, so I belive is ok.

Van Grauw

Ascended (10064)

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02-01-2016, 01:50

I wouldn’t rely too much on the numbers reported by CHKSPD, I don’t know how it measures that speed (and such a round number too), it’s more of an indication, and the Z80 is not always fed from the same clock as the VDP. The sound pitch test would still be good to do, because that is definitely using the same crystal as the CPU.

But anyway, it indeed sounds like a missing M1 wait. Good case there’s some issue between the Z80 and the S1985, either on the path of the M1 signal to the S1985 or of the wait signal to the Z80. Worst case it is a problem with the S1985, and you would have to rebuild the M1 wait logic manually with the help of a 7474 IC (see page 30 of the Z80 user manual).

Van blackmsx

Expert (77)

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02-01-2016, 11:13

I tested the sound with King's Valley and it seems ok compared with a video from youtube.

Then I'll try to build the wait circuit you suggested. Thanks for all the help!

Van sd_snatcher

Prophet (3471)

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02-01-2016, 12:31

blackmsx wrote:

Both pins (38 and 32) from the S1985 are connected to the CPU. There is a 1k resistor (R121) connected between CPU pin 24 and VCC but the resistance measures about 700 ohms.

R121 is a 1K/±5% resistor (gold band), so it's way out of the specification. Try replacing this resistor first.

After you removed the resistor from the PCB, try to measure it again separately and to measure if there's still any resistance between the pin-24 of the Z80 and Vcc. Just to rule out that there's no other factor influencing this change in the resistance.

Van blackmsx

Expert (77)

afbeelding van blackmsx

02-01-2016, 12:48

sd_snatcher wrote:

After you removed the resistor from the PCB, try to measure it again separately and to measure if there's still any resistance between the pin-24 of the Z80 and Vcc. Just to rule out that there's no other factor influencing this change in the resistance.

Yes, the resistor on the board is 1K but when I measured the resistance get 700-750 ohms.

Anyway, yesterday I did what you are suggesting. I took out the original 1K resistor and I put a new one. Both resistors (original and replaced) measure 1K when are unconnected and 700-750 ohms when they are soldered.

I measured also the resistance between WAIT and VCC with R121 unconnected and it gives about 880 ohms.

sd_snatcher wrote:

R121 is a 1K/±5% resistor (gold band), so it's way out of the specification. Try replacing this resistor first.

Do you mean to change the 1K resistor for other value?

Van sd_snatcher

Prophet (3471)

afbeelding van sd_snatcher

02-01-2016, 13:06

Quote:

Do you mean to change the 1K resistor for other value?

No. If there's still an 880 Ohm resistance after you removed R121, so there's something else influencing the /WAIT line. You have to look for that.

Van blackmsx

Expert (77)

afbeelding van blackmsx

02-01-2016, 16:03

What should be the value between /WAIT and VCC when R121 is removed?

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