I have some problems with my gigatron.

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denjhang
Posts: 23
Joined: 02 May 2021, 01:25

Re: I have some problems with my gigatron.

Post by denjhang »

I used the diode position of the voltmeter and found some obvious problems. The voltage value of the ALU part of my Gigatron seems to be twice as large as in the table.
The color-marked columns in the figure are the values I tested. It can be seen that there is no problem with the PC part.
In addition, I tested it when the Gigatron was not connected to a power source.

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Something strange happened. After a few minutes, I tested U25 and U26 again, and the voltage values all returned to the normal range.
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I realized that I grounded the black test lead to test it, and got ridiculous results.
In fact, they are all normal.
Attachments
PC.png
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ALU.png
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Last edited by denjhang on 29 May 2021, 04:57, edited 1 time in total.
denjhang
Posts: 23
Joined: 02 May 2021, 01:25

Re: I have some problems with my gigatron.

Post by denjhang »

The oscilloscope I bought has arrived. I immediately tested CLK2 and CLK1 and got the following graphs. I don't think there is any problem with the clock. I use 1.8432MHZ crystal.
Attachments
CLK.png
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denjhang
Posts: 23
Joined: 02 May 2021, 01:25

Re: I have some problems with my gigatron.

Post by denjhang »

This is the back of my Gigatron, I have checked it at least 5 times.
In fact, I tested all the pins with a voltmeter, and there is nothing wrong with it. :ugeek:
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jbailey
Posts: 29
Joined: 20 Nov 2018, 08:54

Re: I have some problems with my gigatron.

Post by jbailey »

Your clock doesn't look bad, however I will put my Gigatron on the scope too. If I remember correctly their is an offset between CLK1 and CLK2 (ill confirm). While your Crystal should allow the Gigatron to run code and give you the Blinkenlights slowly, it will most likely create VGA timing that most monitors will not understand (as the crystal is supposed to be 6.25Mhz). However you should still be able to press reset on your keyboard and hear a tone (off key, shifted to a lower frequency due to timing).

Tomorrow I will check my ALU diode measurements and post too. You may want to use the schematics to see what is up/down stream of these connections and scrutinize it too.
Hans61
Posts: 27
Joined: 29 Dec 2020, 16:15
Location: Saxonia
Contact:

Re: I have some problems with my gigatron.

Post by Hans61 »

I think the soldered PCB looks neat. I would use a tested and programmed EPROM and RAM just to be sure. I have EPROM's myself with access times that are too slow to get the blinking lights to work even at 2 Mhz clock. I haven't had time to investigate this further. I think it could be the offset between CLK1 and CLK2, which doesn't change because of that (runtime 7404).
I can send you a tested ROM and RAM for 2,50€ each plus shipping costs if it is possible. I live in Germany. I don't know what shipping to you will cost? I would send it as a bubble letter.
Hans61
Posts: 27
Joined: 29 Dec 2020, 16:15
Location: Saxonia
Contact:

Re: I have some problems with my gigatron.

Post by Hans61 »

Somehow translated funny. So with slow ROM run with me the flashing lights even at 2 Mhz not!
denjhang
Posts: 23
Joined: 02 May 2021, 01:25

Re: I have some problems with my gigatron.

Post by denjhang »

:mrgreen:
At the same time, the Omega MSX2 I made can run normally, and this project also uses a large number of TTL chips (74LS and 74HCT series). And these 7400 series chips are also purchased at the same place. This also indirectly proves that those TTL ICs that look like fakes can actually operate normally.
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