[solved] 16/48 OK Composite, but ZX-HD cannot show

[tridy]

Hi.

I have got a 16K ZX Spectrum (Issue 2), and did the composite mod. It seems to be working ok, and I have upgraded the memory to 48K.
The composite now shows the picture but when I connect ZX-HD it shows various artifacts. I can hear that I can type but the picture is full of squares.

Here is a video showing me using ZX-HD:
actually, if I use composite and try to connect DivMMS, it will not work and I will get similar results as with ZX-HD

https://www.youtube.com/watch?v=sWDXp5gWt0Y

how do I go about troubleshooting it? why does the composite work ok?

Thanks!

[Tiger]

Seems it is an "Upper-RAM" fault.
PRINT PEEK 23732 + PEEK 23733 * 256 (Enter) shows 65535? If not, search for the bad IC. If the value is correct - are all RAM-IC's the same type?
Any 4164 200ns will work (even though you are only using 32k or any half of the chip), but can only be mixed with 4532 type chips (Suffix 4 which is the high or suffix 3, which is the low enable, you cannot mix suffix 3 with 4 together).
Any OKI 3732 that may be fitted cannot be mixed with any of the above, also suffix L (low enable) cannot be mixed with suffix H (high enable).
On ISSUE 2 if any Suffix chips are used then set link (top right on IC1 ULA) as follows :-
"For TI chips, set the jumper link right of the ULA to “0v” (middle pad to bottom pad) for chip code ending in “3”, and to “5v” (middle pad to top pad) for chip codes ending in “4”
* OKI RAMs were sometimes used on Issue2 boards – in such cases there will be modification to the 74LS157 multiplexor at IC26. Sometimes this was achieved with daughterboard and sometimes with a double chip socket with clipped/twisted pins.
Valid jumper settings (issue 3+)
Link “TI” and also “3” or “4” (matched with the chip markings, eg: TMS4532-20NL*)
Link “OKI” and also “L” or “H” (matched with the chip markings, eg: OKI3732*-20RS)
(from: http://blog.retroleum.co.uk/electronics ... -spectrum/)"
On the other hand there could be the same compatibility problem with the ZX-HD as with the DivIDE-interface. Look here:
http://benophetinternet.nl/hobby/vanmez ... erface.pdf - or replace the ROM.
Also possible is a "dirty" expansion bus ... (clean it with pencil eraser and after that with isopropyl alcohol on cotton buds or kitchen towel.
Or an NMI-fault within the Z80 CPU (replace it)

[tridy]

Hi. Thanks for your reply.

Code: Select all

PRINT PEEK 23732 + PEEK 23733 * 256

does show 65535.

I will try cleaning the connection ports with a rubber eraser and then alcohol and test it again. I will get back with the results.

[Tiger]

It is also possible that the components at the expansion port reduce the operating power. I found that the ZX Spectrum 48K with an Z80 CPU and 7805 takes approx. 800mA. with an component attached it is nearly 1 Ampere or above. The 7805 has an output of 1Amp (and gets very hot then), so I think the 12V and - voltages break down. Better to take a Z80 NMOS/CMOS type as Z0840008/Z84C008 which reduces the power consumption. A OKI-78SR-5/1.5-W36-C (instead of an 7805) has an IOut of 1,5Amp and doesn't need an head sink. A µA78S05 has also an higher IOut, but it also gets as hot as an "normal" 7805.

[1024MAK]

Most expansions that draw any significant power from the expansion port / edge connector do so from the +9V (nominal) power rail. Hence don’t significantly increase the loading of the +5V supply and hence cause problems for the 7805 voltage regulator.

I don’t have either of the interfaces/expansions mentioned, so I don’t know specifically about these.

What 9V power supply are you using? An original Sinclair unit? Or a different unit? If a Sinclair unit, which model/type?

If the PSU is unable to supply the power required, this will cause problems.

Regardless, it is important to clean the edge-connector. To clean the muck off, use IPA or a solvent cleaner designed for cleaning electronics. Then use a rubber/eraser. The best type is the type designed to remove ink rather than pencil. Finally clean with IPA or a solvent cleaner again. Then carefully inspect each contact for any damage.

Also it’s a good idea to check the female connectors on any interfaces/expansions.

Mark

[Tiger]

@1024MAK you're absolutely right - most expansions take the +9V.
But I don't know with the ZX-HD and the DivMMC. There are some new equipment's which take the 5V (because they take very litte power - but for some Speccy's this little is too much). Best is to check the 12V lane at the ZX with an expansion attached and not attached - if it drops significant the expansion takes too much power ...
There is a hint: https://www.bytedelight.com/?page_id=2264

But that was only a possibility if the cleaning doesn't help.

[tridy]

I cleaned the backside pads of the connection port, and some stuff came off. I was afraid to scrub it harder before so I would not damage them.
I tested it and it works now with ZX-HD and DivMMC!
I also replaced the 7805 voltage regulator with 78S05 5V2A. BTW I had also a question about the power supply being 12V (and not 9V), but from the comments, I see that it is OK.

Now I am waiting for the new replacement capacitors to arrive and I will be done with 48K.

The next thing will be the reviving of the toastrack that I shortened somewhere when soldered in the Stereo Kit from Bytedelight. I will create another post for that.

Thank you very much for your help!

[1024MAK]

Yes, the Sinclair power supply units are unregulated. Hence the output voltage will be higher than the marked value of 9V when supplying less than the full rated output current (power).

Mark

[tridy]

I never owned an original ZX before and besides 12V, it surprised me that the polarity on the power supply jack is different, + is on the outside and - on the inside. Would you say that it is better/safer to use more modern 9V power supplies, or will it be OK with the old 12V one?

[Tiger]

The + outside is as driving on the left - typical British As 1024MAK told the ZX power is unstable and reduces under load. A modern 9V regulator is not necessary.