Spectrum Computing

Were the bent pins on the ULA or the socket? How were they not making a connection? the pins to the socket or the socket to the board? Have you tried replacing the lower ram board with chips, I have to admit I couldn't get the board to work (Same one as yours) just an idea and probably wrong as I a...

MustardTiger wrote: ↑Wed May 15, 2024 8:23 pm Were the bent pins on the ULA or the socket? How were they not making a connection? the pins to the socket or the socket to the board?

Bent on the Socket, socket to board

Hi All, I would like to thank you for all your help its all working now. I have got to admit I feel a bit a knob head admitting this but there nothing wrong with the clock circuit, I has spent a week trying to diagnose the problem and tonight after doing a few more tests it noticed the ULA didnt see...

Can you please disconnect the power, then remove the ULA (I presume all chips are in sockets). Power up again and retest the voltages that you did in your last post. Next, power off again. Now use a test lead to connect R73 left lead to a 0V/ground point. Please ensure you have the correct lead of ...

Can you please disconnect the power, then remove the ULA (I presume all chips are in sockets). Power up again and retest the voltages that you did in your last post. Next, power off again. Now use a test lead to connect R73 left lead to a 0V/ground point. Please ensure you have the correct lead of ...

Cheers

Some pictures of the board, can someone see anywhere I messed up? https://i.postimg.cc/Kk7wytyT/IMG-20240514-131955-040.jpg https://i.postimg.cc/562GZHKH/IMG-20240514-132001-250.jpg https://i.postimg.cc/8FMnhLcY/IMG-20240514-144511-238.jpg https://i.postimg.cc/jDGFwMxN/IMG-20240514-144512-723.jpg ht...

Hi all and thanks for your continued help, I have made some changes but to no avail Changed C26 Changed R24 & R25 Changed TR3 to a MPS2369 Changed Voltage regulator Still the same I have also checked the voltages R73 - 4.89 Right, 2.77 Left R24 - 2.9 Right, 0.79 Left TR3 B - 0.79, E - 0, C - 0 P...

Hi All, I managed to save the images Base https://i.postimg.cc/8jPYQn8Z/Base.png Collector https://i.postimg.cc/G44S98mY/Collec-tor.png Pin 32 ULS https://i.postimg.cc/nCRPHYpp/pin-32-ula.png R24 Left https://i.postimg.cc/v4C2nY4K/r24l.png R24 Right https://i.postimg.cc/1g6Cck63/r24r.png Thanks

dfzx wrote: ↑Mon May 13, 2024 12:01 pm You do need to tell us how you're observing the clock signal and the waveforms around the transistor. If you have an oscilloscope do you know how to capture images from it so you can upload them?

Not really to be honest just got it and trying to learn to use it will have a look at the manual

The type of transistor used in the clock circuit (TR3) is critical. If the turn off time of the transistor is too long, the voltage at the collector will stay low or the output pulse will be short and distorted. ZTX313 have been obsolete for years and the other main substitute is also discontinued....

Hi the clock signal is erratic all over the place the transistor at T3 is a ZTX313 caps and resistors are new.

Thanks

Hi all, I have just built a zx spectrum 48k issue 3b using a new pcb, all IC's, transistors etc are working fine as I have checked them on a known working spectrum, however it doesnt seem to matter what I do the cpu clock on pin 6 is incorrect even though its coming out from the ula on pin 32 ok so ...