Broken interesting Spectrum

Lardo Boffin
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Joined: Sat Nov 26, 2016 2:42 am

Re: Broken interesting Spectrum

Post by Lardo Boffin »

I replaced the two transistors (still one cap to go but I am an optimistic kind of guy), did some voltage tests and look what we have here!

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I think the screen says it all!

To do:-
One last cap
New regulator
Composite mod

There is a bit of a strange start up so not sure if anything else is amiss?

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This appears immediately before the screen goes black and the (C) 1982 message. It is only visible for a split second and took a number of attempts to photo!

Lardo
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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1024MAK
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Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Broken interesting Spectrum

Post by 1024MAK »

Keep in mind that on power on, the RAM may well contain random data. Or if you have just quickly powered down/up, it may still contain some old bits of data. The ULA will immediately display whatever it finds in the display RAM. Next, the CPU reads the code from the ROM. One of the first things it does, is to set the border to white. It then proceeds to do a memory check. The purpose of this check is to see how much RAM the system has. It is not a proper memory test. It is this test that causes the screen to go black, then to have red vertical stripes.
If the CPU makes it past this part of the ROM code, it sets up the system, the end result being the copyright message.

There is a video on YouTube showing a ZX Spectrum starting up, click here

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Broken interesting Spectrum

Post by Lardo Boffin »

Good to hear it’s probably ok thanks.

Are there any Spectrum games with a good ‘attract’ mode? That way I can switch it on and let it go for a few hours for a good soak test.

I ordered one of these:-

http://blog.retroleum.co.uk/smart-card-for-zx-spectrum/

It has a RAM test so will run that as well when it arrives.

Lardo
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Broken interesting Spectrum

Post by Lardo Boffin »

The RAM tests in the retroleum smart card passed ok. That card is awesome for £26!

Any thoughts on the polarity of the remaining cap?

Still RF but Manic Miner doesn’t look too bad!
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Lardo
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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Paul
Posts: 1511
Joined: Thu May 27, 2010 8:15 am
Location: Germanys west end

Re: Broken interesting Spectrum

Post by Paul »

Lardo Boffin wrote: Fri Nov 10, 2017 10:43 am Any thoughts on the polarity of the remaining cap?
You could try with a volt meter.
I guess the Ring indicates minus. If you unsolder it and have a look at its bottom side. If the ring would indicate plus there should be a plus sign somewhere.
In theory, there is no difference between theory and practice. But, in practice, there is.
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1024MAK
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Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Broken interesting Spectrum

Post by 1024MAK »

Your board has the Sinclair recommended upgraded DC/DC converter (inverter) circuitry.
The screen print under the 1uF capacitor will likely have a diode number.
If it is the one that I think it is, it smooths the -5V supply. So the positive lead should connect to the 0V rail and the negative lead should connect to the -V rail.

But I will have to check, as life is rather busy, I won't have time until Tuesday...

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Broken interesting Spectrum

Post by Lardo Boffin »

1024MAK wrote: Sat Nov 11, 2017 12:07 am Your board has the Sinclair recommended upgraded DC/DC converter (inverter) circuitry.
The screen print under the 1uF capacitor will likely have a diode number.
If it is the one that I think it is, it smooths the -5V supply. So the positive lead should connect to the 0V rail and the negative lead should connect to the -V rail.

But I will have to check, as life is rather busy, I won't have time until Tuesday...

Mark
No rush thanks. I remember seeing a D number underneath the capacitor while looking for identifying features. Not near it now to check what the number was but will have a look.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
Lardo Boffin
Posts: 2160
Joined: Sat Nov 26, 2016 2:42 am

Re: Broken interesting Spectrum

Post by Lardo Boffin »

It’s nearly fully refurbed so I decided to replace the face plate and put a new keyboard on - I much prefer the original grey ones to the later dark blue (even though they do work better in artificial light). It looks pretty well!

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ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
sirmorris
Posts: 2811
Joined: Thu May 08, 2008 5:45 pm

Re: Broken interesting Spectrum

Post by sirmorris »

Nice work (as always ; )
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