Broken interesting Spectrum

Lardo Boffin
Posts: 658
Joined: Sat Nov 26, 2016 1:42 am

Re: Broken interesting Spectrum

Post by Lardo Boffin » Tue Nov 07, 2017 11:08 pm

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!

197FA385-6508-4135-9F50-09B5C0C8E56E.jpeg
197FA385-6508-4135-9F50-09B5C0C8E56E.jpeg (4.34 MiB) Viewed 256 times

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?

F80A1A56-FD17-4728-BCFF-CCC096A43A6C.jpeg
F80A1A56-FD17-4728-BCFF-CCC096A43A6C.jpeg (3.11 MiB) Viewed 256 times

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
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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1024MAK
Posts: 1801
Joined: Mon Sep 26, 2011 9:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Broken interesting Spectrum

Post by 1024MAK » Wed Nov 08, 2017 12:10 am

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

Lardo Boffin
Posts: 658
Joined: Sat Nov 26, 2016 1:42 am

Re: Broken interesting Spectrum

Post by Lardo Boffin » Wed Nov 08, 2017 7:15 am

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
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

Lardo Boffin
Posts: 658
Joined: Sat Nov 26, 2016 1:42 am

Re: Broken interesting Spectrum

Post by Lardo Boffin » Fri Nov 10, 2017 9:43 am

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!
081D5003-15A6-4D2F-9120-ECCDFD01867B.jpeg
081D5003-15A6-4D2F-9120-ECCDFD01867B.jpeg (3.39 MiB) Viewed 212 times

Lardo
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

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Paul
Posts: 880
Joined: Thu May 27, 2010 7:15 am
Location: Germanys west end

Re: Broken interesting Spectrum

Post by Paul » Fri Nov 10, 2017 11:15 am

Lardo Boffin wrote:
Fri Nov 10, 2017 9:43 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
Posts: 1801
Joined: Mon Sep 26, 2011 9:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Broken interesting Spectrum

Post by 1024MAK » Fri Nov 10, 2017 11:07 pm

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

Lardo Boffin
Posts: 658
Joined: Sat Nov 26, 2016 1:42 am

Re: Broken interesting Spectrum

Post by Lardo Boffin » Fri Nov 10, 2017 11:31 pm

1024MAK wrote:
Fri Nov 10, 2017 11:07 pm
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.
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

Lardo Boffin
Posts: 658
Joined: Sat Nov 26, 2016 1:42 am

Re: Broken interesting Spectrum

Post by Lardo Boffin » Sat Nov 11, 2017 11:36 am

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!

DAEFF1E4-6773-4C75-A8B9-DED18535CF4D.jpeg
DAEFF1E4-6773-4C75-A8B9-DED18535CF4D.jpeg (717.35 KiB) Viewed 171 times
ZX81 iss 1 (bugged ROM, kludge fix, normal, kit)
Iss 3 with ZXVid, another in nearly perfect box
TS 1000 iss 3, ZXPand AY, ZX8-CCB & ZX-KDLX
TS 1500
TS 2000
Spectrum 16k (iss 1 s/n 1499)
Spectrum 48k
Toastrack + DIVMMC future

User avatar
sirmorris
Posts: 2698
Joined: Thu May 08, 2008 4:45 pm
Location: oxon, uk

Re: Broken interesting Spectrum

Post by sirmorris » Sat Nov 11, 2017 7:52 pm

Nice work (as always ; )
--=== ZXpand+ ... A more moderner all-in-one upgrade solution for ZX81 ===--
* SD/MMC storage * 32K Hires-capable RAM * AY sound chip * Joystick port * Serial *
* BASIC enhancements - plug & play * Reset button * Auto-boot facility *

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