AY sound issue with Just Speccy 128k

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Toki
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AY sound issue with Just Speccy 128k

Post by Toki » Mon May 07, 2018 3:13 pm

Hello there!

Bit of a long shot, but here goes...

I bought one of Zaxon's Just Speccy 128k boards a couple of years ago, and have used it a fair few times for playing games. However, I've only just spotted an issue with it, in that there is no sound from the AY chip, and sometimes a little bit of distortion and the odd quiet beep.

Hadn't noticed until now as I've been playing mostly 48k games and have never owned a 128k. Was trying out a few demos over the weekend though and this is when the problem has become apparent.

Any ideas where I should start looking? Are there any diagnositc programs for the Speccy that would test the AY chip? Could it be as simple as replacing the AY?

Many thanks.
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Ast A. Moore
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Re: AY sound issue with Just Speccy 128k

Post by Ast A. Moore » Mon May 07, 2018 4:46 pm

In 128 BASIC:

Code: Select all

PLAY "c","e","b"
This will fire all three AY tone generators at the same time.
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Every man should plant a tree, build a house, and write a ZX Spectrum game.

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chequered flag
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Re: AY sound issue with Just Speccy 128k

Post by chequered flag » Mon May 07, 2018 5:30 pm

Hello

I have two js128. My first has a green PCB and it is perfect. My second has yellow PCB and had an awful AY output. The problem was four resistors way out of spec. This is what Zaxon wrote to me.
About Ay, check resistors 60,64,63 and 65 it is 4k7 ? Some time ago i wrong put res 470R in my storage box and in one or two boards i fit 470R , correct is 4k7.
Yellow, Purple, Red, is the right colors: 4k7 = 4.7 kohm
Yellow, Purple, Brown, is the wrong one: 470R = 470 ohm = 0.47 kohm

PCB layout here.
http://www.eightbitclone.com/just.html

Resistors just left of Speccy.pl on PCB.

Hope this helps.
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Re: AY sound issue with Just Speccy 128k

Post by Toki » Mon May 07, 2018 6:03 pm

Ast A. Moore wrote:
Mon May 07, 2018 4:46 pm
In 128 BASIC:

Code: Select all

PLAY "c","e","b"
This will fire all three AY tone generators at the same time.
No sound at all when I do this :(
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Toki
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Re: AY sound issue with Just Speccy 128k

Post by Toki » Mon May 07, 2018 6:06 pm

chequered flag wrote:
Mon May 07, 2018 5:30 pm
Hello

I have two js128. My first has a green PCB and it is perfect. My second has yellow PCB and had an awful AY output. The problem was four resistors way out of spec. This is what Zaxon wrote to me.
About Ay, check resistors 60,64,63 and 65 it is 4k7 ? Some time ago i wrong put res 470R in my storage box and in one or two boards i fit 470R , correct is 4k7.
Yellow, Purple, Red, is the right colors: 4k7 = 4.7 kohm
Yellow, Purple, Brown, is the wrong one: 470R = 470 ohm = 0.47 kohm

PCB layout here.
http://www.eightbitclone.com/just.html

Resistors just left of Speccy.pl on PCB.

Hope this helps.
Many thanks for this, I was really hopeful that this would be the issue!

Unfortunately it looks like my board has the correct resistors. Or, should that be fortunately?!


Image
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chequered flag
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Re: AY sound issue with Just Speccy 128k

Post by chequered flag » Mon May 07, 2018 6:34 pm

The resistors seems to be correct.

Because I have no electronics measurement instruments but I do have two js128 I would swap suspected chips (AY chip?) and see if the fault moves to the other machine. That is my reason for two identical computers.

Zaxon has also offered to take my PCB back for repair, but in the end I replaced the resistors myself and it worked.

Maybe contact Zaxon for advice and/or repair?
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Re: AY sound issue with Just Speccy 128k

Post by Toki » Mon May 07, 2018 7:22 pm

Great, thank you.

I already had to send my board off once as it wasn’t working when I first got it.
It was quite costly and postage to France took an absolute age... So I think I’ll try and get hold of an AY chip from somewhere.
I do have one in my Speccy +2, but unfortunately it’s not socketed and I don’t fancy messing with it.
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chequered flag
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Re: AY sound issue with Just Speccy 128k

Post by chequered flag » Mon May 07, 2018 7:30 pm

I got some demos on the SD card that came with my js128.
Run the mescaline demo mescaline_128_plus2.tap and compare it to this video on youtube



that is a good test of the ay-chip.
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Re: AY sound issue with Just Speccy 128k

Post by Toki » Mon May 07, 2018 7:57 pm

Yeah, no sound at all from that, until about 60 seconds in when I just got a loud blast of static.

I found an AY chip for £5, so I’ll see if that fixes anything when it arrives.

Will let you know the outcome, thanks for your help!
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Re: AY sound issue with Just Speccy 128k

Post by Toki » Thu May 10, 2018 7:10 pm

Hmmm... No luck with the new chip unfortunately.

Think I’ll have a careful look over the board this weekend for issues, and then I’ll have to get in touch with Zaxon.
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