8.333MHz oscillator replacement

[archeocomp]

Hi, here is a replacement for hard to find full can oscillator 8.333MHz with duty cycle 50% for XF551 drive. It is based on 74HCT6323A 5 Volt IC. The board has exact footprint of a Full-Can Oscillator. Needed components are 1206 - resistor R1 can be 100k-2M (1M-2M2 tried and working), smaller capacitor C1 is 33p (tried 22p-33p and working), and as specified in datasheet for frequencies higher than 5MHz second resitor is to be replaced by capacitor half the capacity of C2 = that means R2 is capacitor 47p (tried also 68 and 75 and working).
Crystal is double the frequency - 16.666MHz sourced from Aliexpress
https://www.aliexpress.com/item/32867725002.html

 

74HCT6323A is configured with internal prescaler :2. This ensures perfect duty cycle 50%.

Board is shared at OSH Park https://oshpark.com/profiles/archeocomp

 

I have also made prototyping board with THT components, which can be populated with socket pins for rapid experimenting with components values without soldering.

And for those who would need half can oscillator footprint but without prescaler - there are two similar boards (SMD and protoyping THT) shared at OSH Park based on 74LVC1GX04 IC.

Full Can and protoboard

 

Half Can and protoboard

 

Full Can with crystal from Ali

Edited August 8, 2020 by archeocomp

[Wally1]

I prefer solderless upgrades, myself too.

 

nice work.

 

[Jeffrey Worley]

This specific frequency is very hard to find.  Impossible.  I DID find affordable crystals at 8.388608mhz.  The difference is less than 6 tenths of 1 percent.........

I'm trying this to resurrect my Skydata SK-551p disk drive.  The existing 8.333mhz crystal isn't producing anything..

 

best,

jeff

[guus.assmann]

Hello,

 

It's also possible to use a 25Mhz oscillator and devide the frequncy by 3.

 

BR/

Guus

[Jeffrey Worley]

On 12/4/2023 at 12:49 PM, guus.assmann said:

Hello,

 

It's also possible to use a 25Mhz oscillator and devide the frequncy by 3.

 

BR/

Guus

Do you think the 8.388mhz crystal will work?

[+bob1200xl]

I would guess that the tolerance of an off-the-shelf oscillator would be 1%? You're pretty close to that. They use 8.33mhz to sync with a 288 RPM Atari drive. Should not be that picky... A 1050 works OK off speed from 288, right?

 

Bob

 

 

[Simius]

XF551 use 8.333M crystal to sync with 300RPM standard PC drive. The nominal clock of the WD1772 controller is 8M.

300/288 *8 = ~8.333. This is only 4% but it make difference. 8.388M will probably work. It's only 0.6% deviation. 

[Jeffrey Worley]

Thank you for your good news and encouragement!  If this crystal works, I'll have them available for the ask.

best,

jeff