Source for WD2793 Chips

someone · 24-03-2022, 08:17 AM

HEF4521 Frequency divider & oscillator about AUD$2.05 Still an actively available part.

Used delaying feedback from HLD signal assertion to HLT input.
Where:
HLD (Head Load) is used to tell the Floppy Drive to load its head.
HLT (Head Load Timing) is used to tell the FDC that the Head load is assumed to be completed.
The amount of delay is determined by the W2 installed jumper.

CheshireNoir · 24-03-2022, 02:55 PM

Cheers Someone,
Do you know a source for them in DIP? I've been able to find them in SMD (Mouser, element 14) but not in DIP.
If I have to, I can always make a small PCB adapter.

Chesh

***ChickenMan*** · 24-03-2022, 03:49 PM

You can get them from China - $13 for 5 - https://www.ebay.com.au/itm/392628810178

someone · (This post was last modified: 24-03-2022, 06:15 PM by someone.)

Someone doesn't seem to have a spare 4521, however the 4521 is not a critical part and can be substituted with a small circuit comprising of a 1/2 x 74LS123, 220k resistor, 10uF cap as per the 1011 microbee disk controller or even a humble 555 with a few bits.

You could in fact use a manually controlled toggle switch (every time you hear the disk drive head load). LOL!

FUTURELEC has some DIP 4521
They also have a variety of SMD to DIP adapters at seemingly a good price.
SMD Adapters (futurlec.com)

cfbsoftware · 25-03-2022, 06:00 AM

Is the CD4521 a suitable alternative? If so, Digikey has them:

https://www.digikey.com.au/en/products/d...1BE/525976

Ernest · 25-03-2022, 02:04 PM

Should be fine, CD4521 is Texas Instruments as against Philips for the HEF4521.

The board may even work without it, depending on the Drive used, as it is just a head load delay circuit and some drives have the head loaded all the time.

Ernest

CheshireNoir · 25-03-2022, 02:09 PM

So many helpful answers!
Thanks everyone! As I plan to use a Gotek I think head loading is probably not something I'll need to stress about. I have now got a source for pretty much everything. Need to wait for my next pay cycle to source a handful of missing components (And I ran out of solder, of all things!) but I should have enough now to be able to bring my board back to being able to boot off FDD.

Yay!

Chesh