[cctalk] Re: Replacement tachometer sensor for DEC RA80/1/2 drives ...
> -Original Message- > From: Paul Koning via cctalk > Sent: 08 November 2022 01:34 > To: Bob Armstrong > Cc: cctalk@classiccmp.org; Paul Koning > Subject: [cctalk] Re: Replacement tachometer sensor for DEC RA80/1/2 drives ... > > > > > On Nov 7, 2022, at 8:27 PM, Robert Armstrong wrote: > > > >> Paul Koning wrote: > >> Does the tachometer have to be accurate, or does it just have to > >> indicate "spinning fast enough" to satisfy the spin-up logic? > > > > It's not just spin up - the firmware monitors the disk speed all the > > time it's running. > > > > But AFAIK the tachometer has nothing to do with how the bits are > > recorded on the media. It's just there to be sure the disk is > > actually rotating. > > > >> If not, you could just use a 555 to generate a pulse train ... > > > > Maybe, probably, but I'm not sure why you'd want to. That's way more > > complicated than just fixing the tachometer sensor, and having the > > firmware shut down the motor in the event the belt breaks or jams, or > > if the motor brake (yes, it has a brake!) freezes, etc is an > > advantage. It's a fairly big motor and a fairly (by PC standards at > > least) heavy disk - there's a lot of mechanical energy there. > > Indeed, but I was reacting to the statement that the DEC part is strange and hard > to find. So if that turns out to be barrier, faking the tach signal would be a way > to make the drive operational again. The replacement board does not use the DEC part. > > Another approach would be a bit of mechanical work to fit a stock optical > sensor. That would depend on having access to the needed machining skills. That is what this mod does > > paul dave
[cctalk] Re: Replacement tachometer sensor for DEC RA80/1/2 drives ...
> On Nov 7, 2022, at 8:27 PM, Robert Armstrong wrote: > >> Paul Koning wrote: >> Does the tachometer have to be accurate, or does it just have to indicate >> "spinning fast enough" to satisfy the spin-up logic? > > It's not just spin up - the firmware monitors the disk speed all the time > it's running. > > But AFAIK the tachometer has nothing to do with how the bits are recorded > on the media. It's just there to be sure the disk is actually > rotating. > >> If not, you could just use a 555 to generate a pulse train ... > > Maybe, probably, but I'm not sure why you'd want to. That's way more > complicated than just fixing the tachometer sensor, and having the firmware > shut down the motor in the event the belt breaks or jams, or if the motor > brake (yes, it has a brake!) freezes, etc is an advantage. It's a fairly > big motor and a fairly (by PC standards at least) heavy disk - there's a lot > of mechanical energy there. Indeed, but I was reacting to the statement that the DEC part is strange and hard to find. So if that turns out to be barrier, faking the tach signal would be a way to make the drive operational again. Another approach would be a bit of mechanical work to fit a stock optical sensor. That would depend on having access to the needed machining skills. paul
[cctalk] Re: Replacement tachometer sensor for DEC RA80/1/2 drives ...
>Paul Koning wrote: >Does the tachometer have to be accurate, or does it just have to indicate > "spinning fast enough" to satisfy the spin-up logic? It's not just spin up - the firmware monitors the disk speed all the time it's running. But AFAIK the tachometer has nothing to do with how the bits are recorded on the media. It's just there to be sure the disk is actually rotating. >If not, you could just use a 555 to generate a pulse train ... Maybe, probably, but I'm not sure why you'd want to. That's way more complicated than just fixing the tachometer sensor, and having the firmware shut down the motor in the event the belt breaks or jams, or if the motor brake (yes, it has a brake!) freezes, etc is an advantage. It's a fairly big motor and a fairly (by PC standards at least) heavy disk - there's a lot of mechanical energy there. Bob
[cctalk] Re: Replacement tachometer sensor for DEC RA80/1/2 drives ...
> On Nov 7, 2022, at 6:51 PM, Robert Armstrong via cctalk > wrote: > > I have three DEC RA8x drives that have failed (all of them fault with > "spin error") because of bad photo-interrupter tachometer sensors. After > talking to a few friends, it sounds like this is a pretty common fault. > Photo sensors like this are fairly common, even today, but the specific > parts DEC used are weird and unobtainable. Does the tachometer have to be accurate, or does it just have to indicate "spinning fast enough" to satisfy the spin-up logic? In other words, does the actual laying out of bits on the media depend on the tachometer? If not, you could just use a 555 to generate a pulse train at the nominal frequency, perhaps with a second 555 to delay that signal after power up to correspond to the typical time it takes the drive to get up to speed. paul
[cctalk] Re: Replacement tachometer sensor for DEC RA80/1/2 drives ...
May I suggest that you post this to the DEC forum on the VCFED.org website? On 11/7/2022 5:51 PM, Robert Armstrong via cctalk wrote: I have three DEC RA8x drives that have failed (all of them fault with "spin error") because of bad photo-interrupter tachometer sensors. After talking to a few friends, it sounds like this is a pretty common fault. Photo sensors like this are fairly common, even today, but the specific parts DEC used are weird and unobtainable. I designed a little PC board that uses an ITR9606 photo interrupter, a 2N3904 and a resistor as a replacement. Works great - gives a beautiful 5V P-P clean waveform and with the PCB it's a mechanical drop in replacement. Just screws right onto the original mounting holes and plugs into the original connector. I put the PCB design up on OSH Park https://oshpark.com/shared_projects/z8DSkQsP If anybody needs one you're welcome to order some PCBs and build your own. The ITR9606 is as common as dirt, and you can buy bags of ten on Amazon for a few bucks. I've also put a few pictures on the Facebook DEC Computer Users group. I'd post the pictures here, but I don't think cctalk accepts attachments. It's not really worth making a web page for it. Bob
