DivMMCx2 and Spectrum 128k +2 Grey case

[repetto74]

Hi 1024mak,

Here are the pictures. Note that I have already cleaned the port connector of the spectrum without success. The DivMMC has 3 jumpers to be set according to the machine you are using but for the Spectrum 128K +2 settings are the same as for the working ZX spectrum.

[repetto74]

Is there something wrong with this DIVMMC then ?
Any incompatibility? It is featured as working with 128k +2 grey models also.

[1024MAK]

Is there something wrong with this DIVMMC then ?

I don't think it is faulty if that is what you mean.

Any incompatibility? It is featured as working with 128k +2 grey models also.

I'm wondering if the problem is a weak clock signal from the +2 grey that you have. There are at least three PCB versions that are known to exist.
But have not had time to search for more information.

Mark

[repetto74]

Hi 1024mak

My board is an issue 3. I have good knowledge of soldering/unsoldering measuring etc if I known where to look at.
So the fact that programs and games load fine from cassette tape is not related to this weak signal. ?

[1024MAK]

The clock signal is the 3.5MHz CPU clock from the ULA that appears on the edge-connector. I don't know if this signal is used by the DivMMCx2, but some earlier IDE HDD, CF and SD interfaces need this clock signal.

The problem is that the signal from the ULA is not a TTL logic signal and the voltage levels are poor. It's not even close to being a square wave like it should be (in an ideal world). On the Spectrum PCB a transistor boosts the signal, which is then applied to pin 6 of the CPU. But the edge-connector signal comes from the ULA, not the transistor. It's "pin" 8 on the underside.

Interface developers have found it hard to come up with designs that can cope with the various different levels that the clock signal has on the different ZX Spectrum versions. As due to various reasons, each Spectrum version has different levels.

Can you tell me the PCB number that starts with Z... please.

Mark

[repetto74]

Hi Mark,

On the main motherboard I can read 0500 ISS3. There is a smaller PCB located close to the cassette deck mecanism and I read a Z70501 there.

The machine serial number is F-011669 in case.

I have detached the PCB from the case and I can see now on the solder side I do have a Z70500

I think this board has already been repaired in the past. As you can see on the close-up picture the rom is an erasable with UV light and I do not think this was the original fitted. Also diode at D18 has been removed/replaced as it is not sitting flat on the PCB.

As far as I have see over the web there is a mod to increase clock signal on the ZX Spectrum 48k to better accept a Divmmc reader. Do not know if any mod is available for the 128k +2. This is the version for the French market as the main menu is in French.
thanks

[repetto74]

Hi guys,

Replacing the Z80 has solved the problem. The original CPU was missing the M1 line needed for the Divmmc to properly work
Problem solved!