Oh, and the voltage source has to be a constant steady voltage, otherwise you are wasting your time.
Mark
Search found 5153 matches
- Fri May 17, 2024 7:09 pm
- Forum: Hardware
- Topic: Spectrum +2 grey dead short
- Replies: 10
- Views: 353
- Fri May 17, 2024 7:02 pm
- Forum: Hardware
- Topic: Spectrum +2 grey dead short
- Replies: 10
- Views: 353
Re: Spectrum +2 grey dead short
Well, you could try using the voltage gradient testing to try to narrow down the area where the fault is. Every conductor (outside of superconductors) has a small resistance, including PCB tracks. Hence if there is a short circuit, there will be a gradual voltage loss (drop) between the source of th...
- Fri May 17, 2024 2:26 pm
- Forum: Hardware
- Topic: Spectrum +2 grey dead short
- Replies: 10
- Views: 353
Re: Spectrum +2 grey dead short
Shorts on the +5V rail are rather tricky to find, because almost everything is connected to it...
How good is your multimeter?
How many digits and what is the maximum count?
What is the lowest DC voltage range?
Mark
How good is your multimeter?
How many digits and what is the maximum count?
What is the lowest DC voltage range?
Mark
- Fri May 17, 2024 12:49 pm
- Forum: Hardware
- Topic: Spectrum +2 grey dead short
- Replies: 10
- Views: 353
Re: Spectrum +2 grey dead short
Which power rail? Do you mean the (nominal) +9V input?
It could be something simple like an item of metal or a solder splash. If a visual inspection under a good light does not find the problem, then if you mean the +9V, remove the 7805 and TR9. Then retest.
Mark
It could be something simple like an item of metal or a solder splash. If a visual inspection under a good light does not find the problem, then if you mean the +9V, remove the 7805 and TR9. Then retest.
Mark
- Wed May 15, 2024 10:21 am
- Forum: Hardware
- Topic: ZX81 Comp. Mod, no Video
- Replies: 16
- Views: 1011
Re: ZX81 Comp. Mod, no Video
They are only fitted on models sold in the USA. They are to reduce the level of EMI “leaking” out. They are not used on UK models. They do not affect the operation of the computer (well unless broken).
I don’t know the value of them.
Mark
I don’t know the value of them.
Mark
- Tue May 14, 2024 11:41 am
- Forum: Hardware
- Topic: Spectrum 128 Toastrack Mishap
- Replies: 5
- Views: 419
Re: Spectrum 128 Toastrack Mishap
ZTX651 and ZTX653 are suitable replacements for the ZTX650 normally found in TR4 position and when I last checked earlier this year, were still in production.
TR4 normally only dies if there is a short circuit or other overload on one of the outputs of the DC/DC converter.
Mark
TR4 normally only dies if there is a short circuit or other overload on one of the outputs of the DC/DC converter.
Mark
- Tue May 14, 2024 9:49 am
- Forum: Hardware
- Topic: Spectrum 128 Toastrack Mishap
- Replies: 5
- Views: 419
Re: Spectrum 128 Toastrack Mishap
The colour encoder chip is not involved with the RGB output.
Are the +5V and +12V supplies for the video section okay?
Mark
Are the +5V and +12V supplies for the video section okay?
Mark
- Mon May 13, 2024 11:31 am
- Forum: Hardware
- Topic: Newbie question
- Replies: 7
- Views: 422
Re: Newbie question
Soldering is about a combination of good technique and practice.
So start again with a good iron and a cheap electronic kit from say eBay or another source.
There are plenty of tips on soldering both as text tips and help and as videos online.
Mark
So start again with a good iron and a cheap electronic kit from say eBay or another source.
There are plenty of tips on soldering both as text tips and help and as videos online.
Mark
- Sun May 12, 2024 3:45 pm
- Forum: Hardware
- Topic: FIXED Spectrum +2 grey RAM fault but RAM is good
- Replies: 31
- Views: 800
- Sun May 12, 2024 2:22 pm
- Forum: Hardware
- Topic: FIXED Spectrum +2 grey RAM fault but RAM is good
- Replies: 31
- Views: 800
Re: Spectrum +2 grey RAM fault but RAM is good
The joystick chip is believed to be the same as the chip in the Sinclair Interface 2. Hence it's not believed to be essential. The other thing of note, is that the data bus outputs can only drive each data line low (like open collector/open drain).
Well done on making progress
Mark
Well done on making progress
Mark