Super turbo PCB layout

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By gaduke

Supporter (2)

gaduke's picture

30-05-2021, 18:30

I'm very curious about how well this hat PCB works (love the idea). I added this to my most recent JLCPCB order but will hold fire on parts (the QFP Z80 for example) until I hear back from Gregory et al...

By SkalTura

Champion (328)

SkalTura's picture

31-05-2021, 07:33

PCB is made after the schematic from the HansOtten website as mentioned on the first page of this post, so it depends on the reliability of that schematic.
If that schematic works, the PCB should also work...
Can't wait to see the finished product Cool

By Gregory

Master (177)

Gregory's picture

06-06-2021, 15:49

gaduke wrote:

I'm very curious about how well this hat PCB works (love the idea). I added this to my most recent JLCPCB order but will hold fire on parts (the QFP Z80 for example) until I hear back from Gregory et al...

Normally I will be able to test one this week (still waiting for damn parts pfff). So I already stripped a 8250 from its brain. Soldering is straight forward but the legs of the QFP Z80 need to be pushed inwards quite a bit. Hope I will bring you guys happy news, but we'll have to wait and see.

By sdsnatcher73

Prophet (2144)

sdsnatcher73's picture

06-06-2021, 17:43

Very interested to hear how it turns out.

By SkalTura

Champion (328)

SkalTura's picture

07-06-2021, 07:41

Gregory wrote:

Soldering is straight forward but the legs of the QFP Z80 need to be pushed inwards quite a bit.

That's strange... According to the datasheet I downloaded for the Z80, it should fit the layout perfectly...
Wonder if there are different versions of the Z80 QFP ?
For testing I used a PIC16F877A Microcontroller that is also a 44pin QFP, and that also fits easily onto the layout.

By Gregory

Master (177)

Gregory's picture

07-06-2021, 16:08

Well I finished and try to test one today and all I can give you guys is bad news. Put the board in, fired the computer up --> black screen (I'm sure it's supposed to be blue). Tried the switch a couple of times (high frequency-low frequency), didn't help. Things got even worse when I took the board out and replaced it with an ordinary Z80. Again black screen. So I guess something is shorted, maybe when desoldering the Z80. I have taken the motherboard out an give it a check but I don't think it will be soon (guess that service manual will come in handy after all). I won't be trying the circuit on another board until I know what's wrong. Sorry to disappoint you guys (and myself). Sad

By jltursan

Prophet (2533)

jltursan's picture

07-06-2021, 16:58

Ouch, of course the 8250 comes first; but probably you'll also need to check the ST PCB, maybe you can find a short in there (just to help you to diagnose the 8250).

Fortunately, the 8250 is very well documented

By Gregory

Master (177)

Gregory's picture

08-06-2021, 18:03

Yes, it has been done! Everything is working just great. Problem with the circuit not working were part stupidity (some SCART cables work, some don't) and memory loss (forgot to solder a wire). Wished I had found this out before oscilloscoping the board for an hour, well another lesson learned.
Got some photo's for you:
SuperTurbo

Have one concern. I soldered an IC socket on the main board and I soldered the clock circuit with wires to another IC socket, so I could easily get it out when testing. However, this is now a bit to high I think to fit underneath the floppy drives. I was wondering how you guys will do this. If you solder it straight to the board with 1 IC socket, I really don't see a way how to remove the clock circuit in case of a mishap (without damaging the board). You can remove a z80 by cutting the pins, with this circuit it will be very difficult. Like to hear your thoughts on this.
By the way the benchmark was done with 7,3728 Mhz.

By rolandve

Master (254)

rolandve's picture

08-06-2021, 18:21

Looks great, does this mean that my NMS8245 will be able to get a 7MHZ and V9958?

By jltursan

Prophet (2533)

jltursan's picture

08-06-2021, 18:26

Brilliant!

I don't have a 8250; but is it so tight under the floppies?, if so and you can't fit the new CPU PCB, I would try with pin headers instead a standard socket (of course you can use a low-profile one; but they're hard to find). There're low-profile pins that make the build ultra-short, like these
Anyway, beware, the above pins are too big for a standard pad size; so something smaller is needed, I think you got the idea...

Btw, how many flying wires have you connected and where?, why to another IC socket?

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