Spectrum+ 48k repair
Re: Spectrum+ 48k repair
There was modifications on the joystick/sound unit too.
Re: Spectrum+ 48k repair
Hi,
I have now removed the old cpu from the pcb. I don't remember, that is the resistor on the left side of the cpu supposed to be connected to the +5v leg of the cpu. I'll put a picture here so you can get better understanding of what i mean. I just want to be sure.
![Image]()
I have now removed the old cpu from the pcb. I don't remember, that is the resistor on the left side of the cpu supposed to be connected to the +5v leg of the cpu. I'll put a picture here so you can get better understanding of what i mean. I just want to be sure.
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Ast A. Moore
- Rick Dangerous
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Re: Spectrum+ 48k repair
Yes, the resistor is supposed to be there. Here’s one of the pictures I referenced to earlier:
Every man should plant a tree, build a house, and write a ZX Spectrum game.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Re: Spectrum+ 48k repair
Of course the resistor is supposed to be there, i know it, but is it supposed to be connected to the +5v leg through a solder blob?
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1024MAK
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Re: Spectrum+ 48k repair
Yes
Mark
Mark
Standby alert “There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
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1024MAK
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Re: Spectrum+ 48k repair
ZX Spectrum Issue 1 and 2 boards
Extra resistor near the CPU.
This is R73, a 1kΩ resistor connected between +5V and ULA pin 32 / R24 / C67 (D14).
From the service manual:
Extra resistor near the CPU.
This is R73, a 1kΩ resistor connected between +5V and ULA pin 32 / R24 / C67 (D14).
From the service manual:
Markservice manual wrote:This modification is required for efficient operation of certain machine code software and should be implemented on all units. It has been implemented in manufacture for all ULAs 5C112-2 and later.
D14 replaced by C67 (100pF)
R24 changed from 3k3 to 1k
R27 changed from 680R to 470R
R73 (1k) added between IC1/32 and +5V
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.
Re: Spectrum+ 48k repair
This diode snapped in half at some point when desoldering the lower ram chips. Can somebody tell the specs?
![Image]()
![Image]()
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Morpheus
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Re: Spectrum+ 48k repair
Looks like a 47nf capacitor used on the Speccy and not a diode if it came from C4?
R Tape loading error, 0:1
Re: Spectrum+ 48k repair
Never seen a capacitor like that.
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Ast A. Moore
- Rick Dangerous
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Re: Spectrum+ 48k repair
They were pretty common back in the day. A ceramic cap will do just fine in its place, though. Don’t sweat it.
Every man should plant a tree, build a house, and write a ZX Spectrum game.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
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1024MAK
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Re: Spectrum+ 48k repair
I picked up some 100nF (I think) capacitors like that from a surplus supplier (Greenweld) many years ago.
Anyhoo, the machine should still work with it missing. I do however recommend you fit a modern 47nF or 100nF multilayer ceramic as a replacement.
Mark
Anyhoo, the machine should still work with it missing. I do however recommend you fit a modern 47nF or 100nF multilayer ceramic as a replacement.
Mark
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.
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Ast A. Moore
- Rick Dangerous
- Posts: 2641
- Joined: Mon Nov 13, 2017 3:16 pm
Re: Spectrum+ 48k repair
And it doesn’t hurt to combine several capacitors of different values in parallel, say a 47nF and a 1µF one. Each capacitor will operate at a different frequency, because their efficiency is very frequency dependent. In some cases, however, it’s mostly gilding the lily.
Every man should plant a tree, build a house, and write a ZX Spectrum game.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
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Morpheus
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Re: Spectrum+ 48k repair
Did anyone ever fit the 220nf capacitors on the lower RAM to help with the “jailbars” ?
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Ast A. Moore
- Rick Dangerous
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Re: Spectrum+ 48k repair
Every man should plant a tree, build a house, and write a ZX Spectrum game.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
-
Morpheus
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- Location: Hurworth-On-Tees, UK
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Re: Spectrum+ 48k repair
Thinking more in terms of the 48KB models rather than the 128K/+2 but interesting nonetheless.
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Ast A. Moore
- Rick Dangerous
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Re: Spectrum+ 48k repair
Will also work nicely on a 48K Speccy.
Every man should plant a tree, build a house, and write a ZX Spectrum game.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
-
1024MAK
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Re: Spectrum+ 48k repair
On a 16K/48K/+ replace C5 to C8 with 470nF or 1uF multilayer ceramic capacitors
Mark
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.
Re: Spectrum+ 48k repair
Hello people, I know what broke the ZX spectrum. The power supply i mentioned earlier should be outputting 9 volts. I took out my multimeter to test the voltage. And guess what? THAT POWER SUPPLY WAS ALREADY OUTPUTTING SOLID 14 VOLTS!
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Ast A. Moore
- Rick Dangerous
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- Joined: Mon Nov 13, 2017 3:16 pm
Re: Spectrum+ 48k repair
If it’s an unregulated power supply, it’s normal for it to show a higher voltage with no load. Even if it is regulated and outputs 14V under the rated load, that alone shouldn’t have killed your Speccy. The 7805 voltage regulator inside the Spectrum can easily handle input voltages ranging from about 7–8V to 36V. So, no, a 14V input DC voltage wasn’t the primary cause of your computer’s fault.
Every man should plant a tree, build a house, and write a ZX Spectrum game.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
-
1024MAK
- Bugaboo
- Posts: 3115
- Joined: Wed Nov 15, 2017 2:52 pm
- Location: Sunny Somerset in the U.K. in Europe
Re: Spectrum+ 48k repair
A 48K ZX Spectrum draws between 600mA and 700mA (with no expansions connected). 700mA is half the rated capacity of the Sinclair ZX Spectrum 9V 1,4A PSU.
The output of the PSU is required not to drop below 9V at the full load current of 1.4A. The output voltage is not specified at other output current levels.
When connected to a ZX Spectrum, the PSU output voltage is usually between 10V and 12V. You can measure this on the left hand leg / pin of the 7805 voltage regulator chip. Use the metal heatsink tab as the 0V/GND/ground point for your meter.
If the PSU you have been using has similar characteristics, then it is unlikely to have damaged your Spectrum. However, issue 2 boards really don’t like an input voltage of 11.9V or greater (unless they have had their on board DC/DC converter circuitry upgraded).
Mark
The output of the PSU is required not to drop below 9V at the full load current of 1.4A. The output voltage is not specified at other output current levels.
When connected to a ZX Spectrum, the PSU output voltage is usually between 10V and 12V. You can measure this on the left hand leg / pin of the 7805 voltage regulator chip. Use the metal heatsink tab as the 0V/GND/ground point for your meter.
If the PSU you have been using has similar characteristics, then it is unlikely to have damaged your Spectrum. However, issue 2 boards really don’t like an input voltage of 11.9V or greater (unless they have had their on board DC/DC converter circuitry upgraded).
Mark
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.
Re: Spectrum+ 48k repair
Nevermind, my universal power supply has a 9 volt option too.
Re: Spectrum+ 48k repair
The power supply might actually be the culprit, because the picture is much different after swapping out the entire lower ram and the cpu. It still shows garbage but is it normal for the ULA to heat up in the center in under 30 seconds?
Re: Spectrum+ 48k repair
Oh, it heats up in under 15 seconds.