ZX Spectrum stuck before Sinclair copyright message.

[Muttley Black]

Yes! As already said, issues like this one I enjoyed very much. It is great training according my skills level. I am already a winner and he know it!

[Muttley Black]

Don’t worry about A14 or A15 at the moment.
Mark

I start with ULA, to other components continuity test and I found no continuity from A15 (cpu) to pin 27 (ula). Is that normal? The truth is that none of my spectrums has continuity in this line. Just asking to understand the schematic and the way that this line works.

[Ast A. Moore]

I found no continuity from A15 (cpu) to pin 27 (ula). Is that normal? The truth is that none of my spectrums has continuity in this line.

There should be continuity, definitely, but even if there isn’t, this shouldn’t affect the Spectrum running in 16K mode. Keep checking, though.

[1024MAK]

I start with ULA, to other components continuity test and I found no continuity from A15 (cpu) to pin 27 (ula). Is that normal? The truth is that none of my spectrums has continuity in this line. Just asking to understand the schematic and the way that this line works.

A15 should be connected. A15 is used by the ULA in various internal functions including the address decoding.
Do however watch out for errors in the various schematics for the ZX Spectrum. Apart from the ULA, cross check the function and the pin with a pin-out or datasheet. Also, on some boards, the data lines and address lines to the DRAM chips / multiplexer chips, you may find that some of the PCB tracks/connections have been swapped (compared to the schematic) so that it was easier to route the PCB tracks.

So of the known errors may be listed somewhere in the World of Spectrum forums. But finding them is, err, ‘fun’

Mark

[Muttley Black]

There is an error on issue 3b schematic. ULA pin "27" is for sure the pin "37", like you see it on issue 2 schematic. And i have continuity.

[1024MAK]

I do keep meaning to collate details of the errors on the schematics, but I never manage to find the time...

Mark

[Muttley Black]

• I resolder every joint on board

• All ULA databus to lower ram (pins 2,14) have continuity

• All ULA databus to R1-R8 have continuity. Also R1-R8 are in working order

• All R1-R8 to R9-R16 have continuity. Also R9-R16 are in working order

• Both resistor group "points" with ROM databus have continuity

• All ULA address bus +(dramwe) to Lower ram pins have continuity.

• Lower ram lines IC6 to IC3 have continuity

... nothing new!

666 views on this thread. Is it a coincidence? i don't thing so!



How useful would be if i had an oscilloscope in this specific situation?

if I know how to use it, is another question?

[Ast A. Moore]

How useful would be if i had an oscilloscope in this specific situation?

You could check the power rails and determine if there’s too much ripple on each. You could also examine digital signals and see if there are any irregularities. A data analyzer would be even more useful.

[speccyplus]

Wow this thread sounds like mine, gonna try the RAM test, did the OP ever find the issue?

[Muttley Black]

Not yet. Still faulty in my closet. I give it a try when I have time.

[HappyLittleDiodes]

How useful would be if i had an oscilloscope in this specific situation?

You could check the power rails and determine if there’s too much ripple on each. You could also examine digital signals and see if there are any irregularities. A data analyzer would be even more useful.

This was my thought after reading the thread. Is that voltage regulator doing its job?
Also, have you checked your crysal/clock frequencies?

[1024MAK]

The most useful tools when fault finding a ZX Spectrum are:

• A good quality multimeter
• Another ZX Spectrum of the same type to test any suspect chips
• A expansion interface containing a test ROM (the code in the ROM can run without any working RAM, but can still tell you what RAM faults it finds)
• A logic probe (preferably with a pulse detector)
• A logic analyser (an inexpensive 24 channel channel type is most useful, but you can also do a lot with 16 channel versions, but don’t bother with 8 channel versions)

An oscilloscope is useful if you need to see the actual wave shape (wave forms) of signals, but due to the high cost, it is only worthwhile if you expect to use it a lot. However, it can greatly help with some difficult faults that the above listed test gear may not pick up. An oscilloscope is the most useful tool for dealing with problems with any of the analogue circuitry (such as audio and video circuitry).

In terms of test ROMs, there are various types available, two of the best are this one and this one.

Mark