Vaus controller adjustment pot specs?

I'm trying to fix a busted vaus controller. Someone got into it before me at the adjustment pot is mangled. Can anyone tell me what a proper replacement would be? This is VR2 on the board for reference.

Picture of it? I only found the famicom version: http://www.famicomworld.com/forum/index ... ic=10841.0

Actually, if it's single-sided the same way the famicom version is, an additional picture of the back would definitely let me make a schematic. (Someone offered in the past but apparently never got back to us)

No visible part numbers? It's probably possible to search on digikey for an appropriate trimpot...

top right. The yellow piece has

J(symbol)203f

printed on the side. The symbol is a circle with a zig zag line through it.

Is the "zigzag" symbol the old logo of JIS (Japanese Industrial Standards)?

〄


From left to right: Logo of JIS beginning in 1949?; logo of JIS beginning in 2005

it might be that 1949 version if it was printed blurry, but it's more like a stylized S

"203" should mean that it's a 20kiloohm potentiometer.

Any through-hole, top-adjusted, 20kiloohm trimpot should work, if it fits in the geometry. Here's a search for such on digikey.

excellent, thank you so much.

Funny thing! The Arkanoid controller is returning a 9-bit value. (The shift register returns Q8...Q1 for the first eight reads, and Q0 thereafter)

Ok, functional description:

While $4016.0 ("OUT0") is high:
* The CD4040's contents are continuously reset

On a rising edge of $4016.0:
* One half of the 556 starts an analog RC timer ("monostable")
* Specifically, it empties out the capacitor C4 using the 556's DISCHARGE pin.

$4016.0 does not have to be promptly cleared: it'll simply add a fixed negative bias to the result of the conversion, proportionate to the amount of time waited. (Underflow isn't possible)

While the monostable RC timer is going:
* the RC consisting of R1 (3.3kΩ), VR2 (up to 20kΩ), VR1 (unknown range), and C4 (unknown value) converts the angle of VR1 into a time
* The other half of the 556 is a much higher frequency clock ("astable")

The higher frequency clock oscillator
* Uses R3 (1.5kΩ), R3bonus (on the back, 2kΩ), and C2 (unknown) to determine its frequency.
* C1 changes the frequency as it charges. It should stabilize pretty rapidly, and should only affect conversions in the first several seconds.
* Is stopped once the monostable timer completes. (using its RESET input)

When the monostable timer completes:
* One quarter of the NAND gate generates a very short pulse that loads the current contents of the 4040 counter into the shift register
* The exact duration of that pulse is a function of R4 (1kΩ) and C7 (unknown)

Reading from the controller:
* The first eight reads are from the latched values from the completion of the previous conversion
* The 9th (and subsequent) reads are directly from the 4040's Q0 output
** Before the conversion finishes, this provides a direct measurement of the higher frequency clock, toggling every time that clock source finishes a cycle

There is no debouncing capacitor on the button, just a 2kΩ pullup (in parallel with the NES's internal 10kΩ pullup).


FrankWDoom, would you be willing to look for numbers on the various capacitors I've mentioned are unknown? And, if you have a potentiometer, measure the total resistance of the controller's VR1?

That may be part of why Arkanoid has about 12 seconds of unskippable music before the player gets control: an 8-second jingle on the title screen after pressing Start, and then a 4-second jingle before each level. I'd like to be able to add a screen to Vaus Test to characterize the power-on behavior of this in order to determine the implications for controlling the Action 53 menu. But the PowerPak inserts its own interstitial screens (PowerPak title, Game Genie code list, and loading the game), which means the cap is already charged by the time my code gets control.


I previously determined that the monostable timer completes within 7 to 8 ms. This allows reading once per frame, or twice if very careful, but it rules out the sort of rereading typical of DPCM safety routines. Instead, I recommend detecting bit deletions as an out-of-bounds second difference in the angular displacement.


It should be possible to measure this from the NES. Assuming that it takes 512 clocks in 7 ms, that's 315/176 MHz * 7000 us/read * 1 read/512 clocks = 24 CPU cycles per DAC time base cycle. An unrolled read loop at 8 CPU cycles per read should be able to sample the DAC time base at 3 reads per DAC time base cycle. One could try adding a module like this to Vaus Test.

Looking at this more closely, this seems unlikely: the value of C1 can't be larger than about 0.1µF (given the type of capacitor) and the 555's control pin is connected to a 5kΩ resistor to +5V and a 10kΩ resistor to ground internally; that pin should be stable within milliseconds. (2·π·3.33kΩ·0.1µF ≈ 2ms)

Anyway, the same caveat is true for C2, controlling the monostable ramp voltage thresholds, also.

20K Ohms.

I added a "10k-Ohm Micro-Size Potentiometer" from Radio Shack (part number: 271-0282) in line with one of my Famicom Vaus controllers and it was more than enough to fix the range issue. It has the exact same footprint and should work as a good replacement unless you need more than 10K of adjustment range (I didn't even need 6K Ohms).

R1 is 3.3kΩ in the US Vaus controller, but 10kΩ in the Famicom Vaus controller.

Given Tepples's measurements:
* VR1=min, VR2=min, conversion=$0D; VR1+VR2≈0; 3.3kΩ ↔ 13
* VR1=min, VR2=max, conversion=$5C; VR1+VR2≈20k; 23.3kΩ ↔ 92
* VR1=max, VR2=min, conversion=$AD; 173 ↔ 43.8k; VR1 ≈ 40k
* VR1=max, VR2=max, conversion=$FC; 252 ↔ 63.8k; VR1+VR2 ≈ 60k

Unfortunately, the converter is measuring the ratio of ((VR1+VR2+R1)·C4)/(R3·C2), so we can't really extrapolate any further.

( Similarly, R3 is 860Ω (1.5kΩ||2kΩ) in the US Vaus controller, but 1kΩ in the Famicom Vaus controller)

I successfully swapped controller cords between Famicom and NES with obviously different board revisions (even the disconnect was different). Also, the Famicom Vaus was updated with VR2 and other changes we see in the NES version so I doubt there are actually different regional versions other than board revisions applicable to both. I have a Famicom Vaus without the VR2 adjustment pot, a revised Famicom Vaus with the VR2 adjustment pot (no, it's not an Arkanoid II Vaus), and an NES Vaus with the VR2 adjustment pot.

Nothing inside the NES/famicom/cord changes things here. Only the values of the components that I mentioned should have an effect.

There should be numbers printed on all the polypropylene ("chiclet") capacitors, and color bands on the resistors, that would let us get exact numbers for the intended timing. (Most of the color bands I can determine just fine from the pictures, but corroboration is nice)

Right, but what I am saying is that they are pin-compatible so there's no reason to have Japan-specific and US-specific internal specs. It obviously went through manufacturing revisions and I'm sure that they used the latest revision board and component specs for whatever version they were manufacturing at a given time. There is probably not a Japan VR2 spec and a US VR2 spec. There is a rev X spec, rev Y spec, rev Z spec, etc.


I'll check mine too.

This was on the bottom of my older Famicom Vaus VR1:

It was definitely 50k Ohm but it was the earlier revision without the trim pot. My newer revision Famicom Vaus controller with the VR2 trim pot had 40k Ohm, IIRC. I'm pretty sure the NES Vaus I have also has a 40k Ohm VR1 pot.

It looks like a lightning bolt inside a circle to me. I haven't been able to identify the manufacturer.

Looks like a stylized S to me. (Kinda like the safeway logo. I'm certain they never made potentiometers, though)

Sure, but my point is that we have evidence of multiple revisions, and tracking down what PCB changes are of note, even if those changes don't correspond to regions.

The only thing that's fixed is the digital result (because the game expects it), but all the other details I pointed out may or may not be the same from revision to revision.

Right. It's just that you were distinguishing the revisions as "US Vaus" and "Famicom Vaus" when a revised Famicom Vaus definitely exists. I edited out the extraneous details in my quote to make it clearer. Thanks!

The Radio Shack part will work perfectly as a replacement part for OP's VR2 unless he needs more than 10k Ohm adjustment. Even then, adding it with a 10k ohm resistor in series will fix that.

According to tepples's data, the game expects the range of resulting ADC values to vary by about a factor of 3. ($F4 / $84 = 2.9) So the range of resistances also needs to vary by that same range. I.e. Rmax/Rmin = ADCmax/ADCmin = 2.9.

If VR1 = Rmax-Rmin = 40kΩ, then that means that the needed resistance in R1+VR2 is 21kΩ ... so to get away with VR2=10kΩ, you'd need to either replace R1 with something larger (say 15kΩ) or add an additional resistor in series.
If VR1 = Rmax-Rmin = 50kΩ, then R1+VR2 should be 26kΩ.

Probably overthinking it. You only add resistance with VR2 as VR1 wears and loses resistance. The maximum value of a 10k vs. 20k pot only matters if your main pot is so far out of spec that you need to adjust it past 10k.

The plastic knob actually prevents VR1 from reaching either extreme for VR1 anyway. VR2, the trim pot resistor, is only useful for adding resistance when VR1 begins wearing out. For example: you can no longer reach the right side of the screen (maximum clockwise range) in Arkanoid before the plastic knob hits the stop. Removing the knob will sometimes let you reach the right side but adding a little extra resistance with the VR2 trim pot also works. If VR1 goes way out of spec then it is possible that VR1 will not be able to add enough resistance without also impacting the ability to reach the left-most side of the screen. No doubt, this was why they also dropped VR1 to 40k when they added the trim pot, but I've still seen reports of this.

IOW: as long as you don't need more than it's maximum adjustment of 10k ohms, the 10k ohm trim pot will work. No reason not to order a cheaper 20k ohm trim pot online though. The 10k ohm one s just a locally available option for many people.