Zx Spectrum +2 128K black/grey screen. First use in 25 years!

surferneil
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Joined: Mon Aug 30, 2021 10:58 am

Re: Zx Spectrum +2 128K black/grey screen. First use in 25 years!

Post by surferneil »

Hi Mark,

My apologies. I checked that pin 11 again and it was a solid 5.02V. I was not pressing hard enough on my ground.

I have lots of 3.5mm leads. Male to male or male to female.

I have basic soldering skills and I do have a soldering iron.

I don't have a logic probe unfortunately. I might be able to borrow one. Or are the £10 ones from Hong Kong on Ebay any good?!


Neil.
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1024MAK
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Re: Zx Spectrum +2 128K black/grey screen. First use in 25 years!

Post by 1024MAK »

Connect up your audio lead from the tape/sound socket on the ZX Spectrum +2A to a suitable audio amp. Although the ZX Spectrum +2A is mono device, the tape/sound socket is a stereo type, with the same mono signal on both channels. Power on, then see if you can hear the keyboard clicking sound if you use the cursor up or down keys. You may need to turn up the volume. If you hear the keyboard clicking sound, then the Z80A, ROM and RAM are working.

There is a very simple logic probe design here: Build Your Own Simple Transistor Based TTL 5V Logic Probe ;-)

The cheap logic probes from China do often work, but the quality of the construction is often terrible, so they don’t last long :(

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.
surferneil
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Joined: Mon Aug 30, 2021 10:58 am

Re: Zx Spectrum +2 128K black/grey screen. First use in 25 years!

Post by surferneil »

Hi Mark.

I will have the use of a logic probe by Thursday hopefully.

I have connected up an amp. I checked by playing a tape which was very loud. There are no clicks when I press on the cursor up or down or indeed any of the keys.

So I guess that means either one or all of the Z80A, ROM and RAM aren't working ?!

Neil.
surferneil
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Re: Zx Spectrum +2 128K black/grey screen. First use in 25 years!

Post by surferneil »

Mark, I am now the proud owner of a logic probe! Are there any simple checks that I can do on the Z80A, ROM and RAM? Many thanks for your time.

Neil.
probe.jpg
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Re: Zx Spectrum +2 128K black/grey screen. First use in 25 years!

Post by 1024MAK »

To use your logic probe, first select TTL mode. Select pulse mode. Connect the red supply lead to a suitable +5V point. Connect the black lead to a suitable 0V point. You may need to use some leads with smaller clips on to link it up.

Test the following Z80 pins:

Pin Function
6 clock. pulsing rapidly, so both the logic high and logic low LEDs should show at half brightness.
16 /INT (should be pulsing at about 50Hz)
17 /NMI (should be high)
18 /HALT (should be high)
19 /MREQ (should be pulsing)
21 /RD (should be pulsing)
22 /WR (should be pulsing)
25 /BUSRQ (should be high)
26 /RESET (should be high, except for a very short time after power is applied, or when the reset button is pressed and released)
27 /M1 (should be pulsing)
28 /RFSH (should be pulsing)

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.
surferneil
Posts: 11
Joined: Mon Aug 30, 2021 10:58 am

Re: Zx Spectrum +2 128K black/grey screen. First use in 25 years!

Post by surferneil »

Hi Mark,

Many thanks as always for your time. Most of the tests were correct, apart from the two highlighted.

Just to check though. I assume that when it should be pulsing you should get both lights on?

On the 16 pin it was red (high) on and on the 19 pin it was green (low) on.

Fascinated to hear your thoughts. Really enjoying the testing and have been having a lesson on basic computing with my son which is great!!

Neil. (in sunny Devon)


6 clock. pulsing rapidly, so both the logic high and logic low LEDs should show at half brightness. Yes. Red and Green about half brightness, no beep
16 INT (should be pulsing at about 50Hz) No. Red bright, Beep.
17 NMI (should be high) Yes. Red, high, beep.
18 HALT (should be high) Yes. Red, high, beep.
19 MREQ (should be pulsing) No. Green, low beep.
21 RD (should be pulsing) Yes. Red and green. Beeping.
22 WR (should be pulsing) Yes. Red and green. Beeping.
25 BUSRQ (should be high) Yes. Red beeping.
26 RESET (should be high, except for a very short time after power is applied, or when the reset button is pressed and released) Yes. Perfect. Went green with RESET and then immediately to red.
27 M1 (should be pulsing) Yes. Red and green. Beep.
28 RFSH (should be pulsing) Yes. Red and green beep.
surferneil
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Re: Zx Spectrum +2 128K black/grey screen. First use in 25 years!

Post by surferneil »

I've been enjoying my new Logic Probe!!
Spectrum Chips copy.jpg
Checked out the four chips on the bottom of the board. No idea if this is helpful!

H=HIGH L=LOW B= BOTH (pulsing?)


One other thing that I have noticed now that I turn the machine on after it is connected it that you get a black rectangle with a pink border for about half a second when you power up and then it goes to a dark grey screen with no border.

Thanks Mark.
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