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Hello everyone, I encountered some issues while working on the Apple 1.
1：It powers on and displays "@_@_@_@_" but does not blink (Figure 1).
2：When I press the clear screen key (B4-12 connected to 5V), the screen does not display anything. When not pressed, it shows "@_@_@_" (Figure 2).
Except for the 7450, all the other 74-series chips are from the Chinese manufacturer HLF.
That does not look too bad.
Terminal sections seems to work basically, you get an alternating pattern of "_" and "@" that is very good and that clear screen works, that is also good.
Looks like it's really only the blinking that is missing.
I even would assume more will work, just with a none blinking cursor.
You need to check the output of ICD13 (NE555) on Pin 3 it should alternate 150 ms low "@" and 300 ms high " ", and cursor frequency is around 2,18 Hz
Are R10 and R11 10kOhm and C7 22µF ?
What measurement equipment do you have availible?
A DigitalVoltMeter is often to slow, to show the blinking, an analog Voltmeter will show that fine.
If a DVM is all you got please connect a LED with a 1KOhm resistor as pictures above to Pin 3 and Pin 1.
The LED should be lit when " " is shown and off when "@" is shown".
At the moment I would expect the LED staying off, if that is the case and R10 and R11 are in 10kOhm and C7 22µF the NE555 is likely broken.
I see the PROMs are not populated do you have any external ROM replacement?
When the CPU part is working a press on Reset after Clear Screen should show "\" first postiion first line and the a Cursor "@" should be blinking in the first position of the line 2.
You can compare with this: https://www.scullinsteel.com/apple1/
The 74xxx parts are quite uncritical but the 2513, 2519 and 2804 parts are hard to get in working, none fake condition.
But yours seem to work at least as far we can tell with the information that you provided so far.
It would be nice if you let us know from which country you are because here are people from all over the world, and it can be very helpful if you find some one with another Apple 1 in your country.
Hello, I am a student at a vocational school in China.
I used 10 kΩ for R10 and R11, and 22 μF for C7.
The NE555's Pin 3 shows a frequency of 10 Hz when measured with an oscilloscope (Figure 1).
I am using a PROM adapter board from P-LAB (Figure 2).
After replacing R10 and R11 with 2 kΩ and C7 with 100 μF, the issue remains unresolved (Figure 3).
I have an oscilloscope with an analog bandwidth of 30 MHz and a maximum sampling rate of 200 MS/s, a logic analyzer made with a Raspberry Pi Pico with 22 channels, and a digital multimeter.
Figure 1.jpg
Figure 2.jpg
Figure 3.jpg
So myguess Japan, that I took because of the nickname, was wrong, but at least asian region was correct.
10 Hz is a fast flashing that would look more like a gray @ instead of a blinking one.
2kOhm, 2kOhm and 100µF you selected should result in 2.4 Hz with 280 ms high and 120 ms low https://ohmslawcalculator.com/555-astable-calculator
It seems your NE555 behaves strange, do you have a replacement?
What you can do, take the NE555 out of the socket, take a 2k resistor and bridge pin 3 via the resistor alternating to pin 1 and pin 8.
In other words blink manualy.
Does that work?
My 2 cents: I've built probably a dozen Apple-1s and on none of them did the startup grille blink on first startup. The blinking appeared after 3-5 minutes of operation and never went away if I used my replica at least once every 2 weeks. Later I realized what was wrong, my Philips 22uf capacitors were almost dead and showed very low ESR.
I tried these two methods (replace NE555 and generate pulse manually with 2K resistor), but the problem still does not flash is related to my AM1404 or 2519 adapter board
You said when you press clear or simulate that with shorting two pins the screen wents black. If that is the case almost certainly both the line 2519 and the 6 screen character buffers are working.
One question if you stop pressing Clear the screen stays clear or instantly fills again with the @_@_ pattern?
If the pattern comes back it means something is wrong with the the AM1404 or the DS0025.
There is one AM1404 that stores the cursor position C11B.
Question is does the reaction change when you remove that one?
If you exchange it with one of the other Am1404 does everything works same or no change?
Here is somewhere a thread that describes in more detail what happens when certain chips are missing or broken.
So far we can only say the bits used by @ _ and Space seem to work.
Could you adjust the blinking to 2Hz?
If yes, follow the signal it enters C12 on Pin 1 and leaves it on Pin 3. It enters C10 on Pin 2 and leaves it on Pin 1.
Where does it stop pulsing?
I would recommend to build a Tester For the Am1404/2804 https://www.applefritter.com/comment/112595#comment-112595
ne555pin3.jpg
0025pin5.jpg
00255pin7.jpg
The Output of the DS0025 does not look good at all.
But you set the timebase to 1sec per devision that will give random results!
The Clock we want to observe has the frequency of half the Character Rate.
14.31818 MHz (Crystal) divided by 2 (C13) gives a Dot Clock of 7,15909 MHz
The Dot Clock divided by 16 (D11) is 447,744 kHz what means a periode of 2,233 µs.
To see something useful the timebase needs to be set somwhere betwenn 1µs and 10µs per devision.
This estimation ignors the the border and traceback times.
Bild_2025-08-29_102541322.png
Confusion alert: what is called on the picture above ø1 and ø2 is called on the Apple Schematics ø3 and ø4 as the other clocks two are already assigned to clocks used by the CPU.
On Pin 7 and Pin 5 you should see a signal like above.
This signals are switched off when the video Signal is drawing the boarders or is in the trace back phase.
The outputs of DS0025 are not TTL the signal oscillates somewhere between -12V and +5V, nominal -11,3V and 4,3V ! Your Y-scale of 5V per devision, should be fine.
I don't have a Apple 1 so I cannot do reference measurements, sorry.
To your first picture that looks like we have a flashing of around 2,5-3 Hz that is a bit faster but should be visible.
Here you find some hints what happens when you pull specific chips: https://www.applefritter.com/comment/112475#comment-112475
But as first recheck the DS0025 output with proper settings.
The DS0025 controls the clock of all seven DIP-8 shift registers with out a propper clock they can not operate. And the output would be fixed as they do not circulate.
Your 2519 Adapter Board and also the 2513 Adapter Board is with a certainty of 99% working perfectly.
If the 2513 would not work screen would be filled with white stripes or black instead of with @_@_.
When the Clear clears the screen as long as the connection is hold then the 2519 works as well, it's also needed to display a full characters if it is not working you would see broken characters.
So please assume this two parts are working perfectly.
0b154b65564220e7f0f22ce11b563379.mp4
It's absolutely possible that you have a problem with C13 or C14 too that prevents the blinking but
C14 Pin 12 Zd toggels between Pin 14 IOd (GND) and Pin 13 IId (Cursor) depending on the state of Pin 1 S (/WRITE)
That is some kind of a Chicken Egg problem, as the cursor is need to generate /WRITE.
The cursor is stored and circulated around in C11B if the the two clock signals are not working that does not work as well.
So please check if DS0025 is producing the two clock signals if it does not all AM2804/2504/1404 chips including the cursor are working.
Please have a look to Pin 13 of IC14 if that is high or toggeling between high and low you can do the following:
Bend Pin 1 of c14 out of the socket you can connect it with 1 or 2k resistor with GND (low) or 5V (high).
Depending of that the logic level of Pin 13 (Cursor) or Pin 14 (low) gets output on Pin 12.
If Pin 13 if C14 is always low C13 74175 might be broken or more likely Pin 13 D3 has a constant level what would be caused by C11B.
It can be a broken 2504/2804/1404 in position C11B or the missing clocks (you guessed it) on the output of the DS0025.
In the Video you flashed the Vertical Blanking Signal that generates the borders that signal is or-gated with the CLEAR input and send as CLR to Pin 15 of C4 and C14.
In other words outside the visible 25 lines the CLEAR button is automatically pressed.There for we can assume that both 72157 at position C4 and c14 work fine.
Okay, then should I go check the part about ds0025 next or go check these two ICs, c13 and c14? I think I should check ds0025 first. What do you think is more appropriate?
First you check if the inputs of the DS0025 are toggling. Actually you are checking the parts above on the schematics. If you have something on the input you can expect having also something on the output so the idea is to measure input and output same time and compare on a dual channel oscilloscope.