A Grand Day Out

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rubber_jonnie
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Re: A Grand Day Out

Post by rubber_jonnie »

stephen_usher wrote: Tue Feb 06, 2024 12:17 pm
rubber_jonnie wrote: Tue Feb 06, 2024 10:30 am So should be back together and fingers crossed with a working tape deck soon. What's interesting is that it seems like the external cassette connections appear to rely on the internal cassette deck for the amp circuit, which surprised me a bit.
Why duplicate the circuitry? Sounds like a smart thing to do as then the computer only needs a single input and doesn't need extra circuitry itself.
I'd agree to some extent, but if you remove the cassette unit, which is a modular part, the on board cassette ports will cease to work and won't have any options for program loading/saving.

And both inputs fail if the cassette unit fails. I suppose it was probably always cheaper to just replace the cassette module than start digging into the mainboard.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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stephen_usher
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Re: A Grand Day Out

Post by stephen_usher »

The alternative would be to move the amp onto the motherboard, which gives similar problems if that circuit fails.

Of course, the designers never thought that someone would want to run the machine without the tape drive fitted as that's how it would always be supplied.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
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rubber_jonnie
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Re: A Grand Day Out

Post by rubber_jonnie »

stephen_usher wrote: Tue Feb 06, 2024 1:59 pm The alternative would be to move the amp onto the motherboard, which gives similar problems if that circuit fails.
Indeed, it is problematic, so I do prefer it this way, just 2 screws and a plug to get the unit out for disassembly
stephen_usher wrote: Tue Feb 06, 2024 1:59 pm Of course, the designers never thought that someone would want to run the machine without the tape drive fitted as that's how it would always be supplied.
Indeed.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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PhilC
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Re: A Grand Day Out

Post by PhilC »

Any luck then @rubber_jonnie
If it ain't broke, test it to Destruction.
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rubber_jonnie
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Re: A Grand Day Out

Post by rubber_jonnie »

PhilC wrote: Tue Feb 06, 2024 7:24 pm Any luck then @rubber_jonnie
Not today I'm afraid, work was uber busy and then I had training, and I'm up in the morning at 05:30 to go into the office, so early night tonight.

May be Thursday before I can take another look, but still waiting on the uPC358C's anyway. I did manage to give the whole machine a good clean though and it looks great.

Very good build quality compared to other contemporary machines.

Just a bit weird from the OS situation, even BASIC needs loading from tape.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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rubber_jonnie
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Re: A Grand Day Out

Post by rubber_jonnie »

I have put the demon OSI600 to one side, so I will be looking at the MZ-700 next, see if I can figure out at which point the cassette input fails.

More on this later.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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rubber_jonnie
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Re: A Grand Day Out

Post by rubber_jonnie »

Well thats a bit weird.

The MZ-700 has a great service manual, puts others to shame and gives these waveforms and tells you the test points to look for them:

Screenshot 2024-02-09 at 00.00.32.png
Screenshot 2024-02-09 at 00.00.32.png (1.06 MiB) Viewed 212 times

Said test points can be found here on the schematic:

Screenshot 2024-02-09 at 00.02.02.png
Screenshot 2024-02-09 at 00.02.02.png (1.47 MiB) Viewed 212 times

And the PCB has a decent silkscreen making part location and therefore test points, easy to find.

The trouble is, I get zero signal at TP 1. Just nothing. I did move on to look at TP 2 & TP4 , but given there was nothing at TP1, I wasn't surprised I found nothing, since TP1 was flat.

I will compare with another cassette deck to see what the resistance should look like for the head, as even connecting the scope directly to the head read nothing, so that feels suspect.

It doesn't quite answer the question of why the external cassette doesn't work, though if it is using the same circuit on the cassette and that is bad, then all bets are off.

There is 5v at the op amp, before anybody asks. Bit of a head scratcher.
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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HigashiJun
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Re: A Grand Day Out

Post by HigashiJun »

I've been away for a 5 day business trip abroad only to discover that our fellow member @rubber_jonnie got two retro machines meanwhile...

:D
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stephen_usher
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Re: A Grand Day Out

Post by stephen_usher »

Don't go away again, he'll get more! ;-)
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.
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rubber_jonnie
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Re: A Grand Day Out

Post by rubber_jonnie »

stephen_usher wrote: Fri Feb 09, 2024 10:32 am Don't go away again, he'll get more! ;-)
You know me so well :)
Collector of many retro things!
800XL and 65XE both with Ultimate1MB,VBXL/XE & PokeyMax, SIDE3, SDrive Max, 2x 1010 cassette, 2x 1050 one with Happy mod, 3x 2600 Jr, 7800 and Lynx II
Approx 20 STs, including a 520 STM, 520 STFMs, 3x Mega ST, MSTE & 2x 32 Mhz boosted STEs
Plus the rest, totalling around 50 machines including a QL, 3x BBC Model B, Electron, Spectrums, ZX81 etc...
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