Spectrum+ 48k repair
Re: Spectrum+ 48k repair
I haven't read the whole thread, but did you change the capacitors? With problems like these, you might as well start there. That way you can rule that out as a potential problem.
Re: Spectrum+ 48k repair
Recapping was the first thing i did.
Re: Spectrum+ 48k repair
Hi everyone, i got 2,98 volts on the pin 1 of the lower ram. The other voltages were good.
Re: Spectrum+ 48k repair
That should be -5V, so that's obviously not good! No wonder your lower RAM isn't working.
I was looking at how the voltage generation circuity functions just the other day, but it's already evaporated out of my head...
The alternative to fixing the -5V generator is to fit a lower RAM replacement board, which doesn't need -5V.
I was looking at how the voltage generation circuity functions just the other day, but it's already evaporated out of my head...
The alternative to fixing the -5V generator is to fit a lower RAM replacement board, which doesn't need -5V.
Re: Spectrum+ 48k repair
I already have the lower ram replacement board soldered in
- Ast A. Moore
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Re: Spectrum+ 48k repair
And what do you get on the collector TR4?
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
The ULA warms up so much that it's painful to press your finger against it for over 5 seconds.
Re: Spectrum+ 48k repair
My probes are too big to get in there. But i'll try.
Re: Spectrum+ 48k repair
Almost 9 volts
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Re: Spectrum+ 48k repair
I don’t have a working issue 2 board to hand at the moment, but the ULA in an issue 1 board (soldered in) is similar. From being left switched off at a room temperature of about 20°C, and then turning it on, I can hold my finger on the central area of the ULA chip for only 37 seconds before it gets uncomfortable, then a few seconds later I have to remove my finger.
Once it has been on for a while, I can only hold my finger on the centre section for about five seconds.
It’s normal for these ULA chips to run hot. The internal temperature of a silicon chip can rise to around 100°C to 125°C and they will still work.
Part of the reason that this design of chip gets so hot, is that internally it operates at a voltage much lower than +5V. Around all four edges of the silicon chip inside the plastic package, there are lots of series pass regulators. Each of which produces lots of heat on their own. Plus there are lots of bipolar transistors switching at high speeds, these form the bulk of the digital circuitry, all of which produce a fair amount of heat as well.
For comparison, most modern chips use CMOS transistors, which run much cooler. In fact, a CMOS chip that is NOT running at a very high clock speed is cool to the touch.
So don’t worry about the temperature of the ULA.
Mark
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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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Re: Spectrum+ 48k repair
The -5V supply (pin 1 on the lower RAM sockets) should be between -4.45V and -5.1V.
Can you please post up the actual voltages you get on the +5V, +9V and +12V rails please.
Do you still have a heatsink on your 7805 voltage regulator? If yes, the machine screw holding it in place nice and tight? Or have you fitted a more modern DC/DC converter switching type?
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.
“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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Re: Spectrum+ 48k repair
On pin 13 of the ULA in an issue 1 board, I get 2.9V soon after power up, with the voltage rising slowly a little bit.
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.
“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
Pin 9 5.01 volts, pin 8 12.14 volts, pin 1 4.80 volts (lower ram)
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Re: Spectrum+ 48k repair
Those voltages are all fine
Mark
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Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
“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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Re: Spectrum+ 48k repair
Strange
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Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer later in the year.
“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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Re: Spectrum+ 48k repair
@Slauri
Can you please post a photo of your Spectrum board as it is now.
Mark
Can you please post a photo of your Spectrum board as it is now.
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.
“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
Everything I have replaced:
1)electrolytic capacitors
2)the entire lower ram
3)zilog z80 cpu
1)electrolytic capacitors
2)the entire lower ram
3)zilog z80 cpu
Re: Spectrum+ 48k repair
I don't know what to do.
- 1024MAK
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Re: Spectrum+ 48k repair
Can you please take a close up photo, under good light, of the underside area of the board where the 4116 DRAM chips are.
Mark
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.
“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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Re: Spectrum+ 48k repair
I’ve enhanced your picture and marked a few areas that I suspect might be solder bridges/shorts:
Perhaps Mark will be able to see more. I’d remove the lower-RAM board and inspect the traces on the logic board underneath it.
Perhaps Mark will be able to see more. I’d remove the lower-RAM board and inspect the traces on the logic board underneath 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.
Re: Spectrum+ 48k repair
I've cleaned the board multiple times with alcohol. Those bridges weren't there before. Maybe they have come from my workdesk? I have not cleaned it for a while. Some of those may look like bridges but they are just reflections of the soldering mask that has melted away due to my bad soldering skills.