Spectrum Computing

I could guess, but would prefer you to take some better, higher resolution photos. I could then work it out.

Mark

Yeah, the coil being correctly connected is rather essential to the operation of that circuit

If you need any more help, shout out.

Mark

Assuming you still have a 7805 voltage regulator IC (or equivalent DC/DC converter) fitted, then yes there should be +12V and -5V power feeds at the 'lower' DRAM sockets.

Mark

For transistors, the convention when identifying their terminals/leads is to show them as viewed from below. See this post . Or these datasheets for the ZTX650, ZTX651 (link to PDF) and ZTX653 (link to PDF) . Or this datasheet for the ZTX751 (link to PDF) BTW, they look to be correct in your photo :...

In reality, it does not really matter if TR7 collector is supplied from the +5V or +9V rail. TR7 is being used in an emitter follower configuration, and when used like this, the emitter voltage is always slightly lower (around 0.6V) lower than the base voltage. As the base voltage is either coming f...

This forum does not allow attachments. Hence photos, pictures, diagrams, program files, documents etc. all need to be uploaded to other sites. Then you need to link them or if it is an image type recognised by the forum software, you can use the photo icon.

Mark

I simply have no idea where to start... Can you advise me on the best course of action in such a situation? :) Apart from a multimeter, do you have any other test gear? Ideally the next step would be to carry out some tests using an oscilloscope. Check IC1 (ULA) pin 32 and IC2 (Z80A) pin 6 to see i...

Try this: Mark

Do you get the keyboard click sound if you press keys?

Are you connecting via RF/UHF TV out from the modulator, or has it been composite modified?

By no signal, are you getting just static / blue screen, or a black screen?

Mark

No, the controller will not damage the ZX Spectrum or the joystick interface. There may however be a snag with some Kempston or Kempston compatible interfaces. These were developed when joysticks were just mechanical switches. Hence the electrical polarity did not matter. For joysticks and controlle...

See my blog page for the values for the final Sinclair modification. Note that the schematic on this page shows both the original configuration and the new positions of the changed and new components. Read the notes to understand the diagram. C49 should be 560pF. C77 should be removed if the circuit...

C77 and C49 are small value capacitors and are fairly robust electrically speaking. If they show no signs of physical damage, they are likely okay. However, C43 is critical to the operation of TR4.

Mark

The ‘certain mod’ is an upgrade to the DC/DC part of the on board power supply circuitry. As the +12V and the -5V rails are okay, no need to get distracted by this. It’s an official Sinclair modification. TR7 is only used for the bleeper. The type used is not critical as long as it’s an NPN type. Al...

It’s better to have a separate thread for each fault so that there is no confusion. Based on the voltages you have posted, TR5 is fully “on” because the +12V rail is low, this is correct. TR4 appears to also fully on (it should not be continuously fully on). Or there is a short circuit to 0V/GND. Or...

Link works okay for me.

Thanks for the guide

Mark

Because there are numerous errors on the schematics for the various different issue boards, I normally compare one with another. And/or check the service manual. R59 is specified as a 2% tolerance 1.8k resistor. This may not be clear on some diagrams. Good to know that this board is now working :D M...

I would give a vote for the ulaplus too, but that's all. Seems it would have been made with the technology of the time with a somehow double sized and more expensive ula, but it's simply a palette changer, retains the loved 2 colors limitation for each 8x8 cell, so not really legit but I fell it ve...

TR4 base acts as a silicon semiconductor junction. The turn on voltage is just over 0.5V (measured between the base and emitter terminals) and depending on the circuit, it could go a bit higher. You should however, never see a voltage here much above 1V. This is a complex circuit. TR4 when working n...

Don't forget, the human (and various other animal) nervous system also uses electrical signals...

Mark

If that happens, best get your bids in fast for some space in an underground cave/mine/tunnel or similar...

Mark

Atari STFM and various other computers sold in the USA or other countries where EMI regulations are/were quite strict will also have or likely have either steel cases or internal steel shielding. However, there are still plenty of holes in these cases/shields. Plus of course the mains cable and thos...

It's semiconductors that are most affected, that would include Z80 and 6502 processors, DRAM, SRAM etc. Equipment that only uses resistors, relays, coils, non-electronic regulators, motors etc. may well survive if far enough away. Normal military grade semiconductors would also die, as these normall...

What is a copy and what is not a copy? What is a derived work? What about an item inspired by another item that is copyrighted? Ultimately all humans learn by copying. If a child decided to paint a picture of a photo, would that be a copyright infringement? Copyright is only supposed to protect the ...

TR4 is a bipolar NPN transistor, so it’s more useful to refer to the three terminals/leads by the junction names: c - collector, b - base, e - emitter. https://i.postimg.cc/Jt653ykd/E209867-A-D2-DF-4781-A82-D-9-E1246-AD0-D48.jpg In this circuit (TR4), the emitter is connected to the 0V/GND/ground ra...