Spectrum Computing

AndyC wrote: ↑Wed Sep 11, 2019 8:51 am Could be a redesign to fit in better with the QL perhaps?

That is what I suspected too.

I just got a seemingly unused microdrive and it has a shield without the rainbow. I have never seen these before, does anybody have information about them?

So, something is causing the Z80 to run slowly. If the clock signal on pin 6 is good (correct frequency and goes sufficiently high, as in within 100mV of the value of the +5V supply voltage) then maybe it is a control signal being active which is interrupting the Z80. So check: Pin 16 (/INT) should...

I can confirm 3.5MHz on pin6
C27 is 1uF 63V
R31 is 220K
I also checked the tracks between all involved components. Only unchecked component is C26.
Won't be able to check anything before tomorrow night.

One more thing I just discovered.
When I discharge C27 before I turn on the Spectrum, I always get a black screen with white border and after exactly 30 seconds I get the following screen:

Thanks Mark. I am getting a bit frustrated with this Speccy :( Here is what I did so far: - cross checked ULA - replaced TR4 (now with ZTX651) and TR5 (ZTX751) - replaced TR3 (restored the 3.5MHz to CPU) - changed the regulator - recaped the board - desoldered the upper RAM and their logic ICs (to r...

I just took out my scope and looked at the clock signal. The ULA puts out 3.5MHz at pin32, but the CPU only sees a 5V signal at pin6.
This probably means TR3 is dead, correct? Unfortunately, I don't have anything here to replace it right now....

The 5V on IC23 didn't make a difference. When the machine gets warmer (it is 36 Celcius right now here in Germany :shock: ), I seem to get a light border. https://photos.app.goo.gl/3ja79qp3qv9Dpu8i8 What is the wire on the back side doing? Next thing I would try is checking the ROM since it is socke...

dfzx wrote: ↑Tue Jul 23, 2019 11:39 am If you mean to ask whether you need to remove the power while you make that IC23 connection, yes, do it with the machine powered off.

I seem to recall someone else started poking at pins with the machine powered up a few months ago. Not a good idea unless you have a very stready hand.

Can I just connect +5V to pin5 of IC23 without removing any connection?

Thanks, I will try this. I forgot to mention that the ULA is fine. I tested it in a working model.

Hi, since I already used post #1 for a help request, I want to make sure that #2 is about saying hello to everybody. I am 53 years old and German. My first computer was a 16K Spectrum which set me down a non mainstream path here in Germany where everybody had a VIC20 or C64. There was pretty much no...

Hi, my first posting here is already a request for help, sorry. :roll: I got a 48k issue 2 that had a faulty TR4 (ZTX650) which I replaced with a 2N3904 that I had here. After checking the voltages at the 4116s look okay, but it does not boot to the logo. Instead I get black and yelow bars on the sc...