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RK05/RK8E Restoration

bobaboba

Experienced Member
Joined
Sep 7, 2013
Messages
400
Location
Scotland
The TU56/TD8E is running well now. I have been given some DecTapes, used Dump/Restore to get OS/8 running from it, and I can run a system - even Fortran IV, although that certainly gives the tape a bit of a workout doing the compile and load!

So now onto the next phase with the RK05. I've removed all traces of DEC's infamous black foam. Even the seal round the blower had disintegrated to dust. Stripped the blower and washed out the impeller. Removed the absolute filter and blew it out backwards to clean it out a little. I don't have a prefilter, not even the metal case for it but I don't suppose that matters too much in the short term. Cut some replacement seals from foam for the blower and the seat for the cartridge inlet. Cleaned the brown dust off the heads. Replaced the retract battery which had made a bit of a mess. Cleaned everything - even the drive belt had adhered pretty firmly to the pulleys - and finally fired it up. No smoke, the airflow seems fine, the switches and lights work and if I push the microswitch the spindle runs up OK with no squeaking.

Next I tried the diskless controller test last night which failed early on with a Data Register fail. Easy to track down and fix though so by close of play the RK8E passes that diagnostic and I'm ready to start in earnest on the RK05. This needs a little care because disk packs for the 8 are scarce and new heads even scarcer. The next big step is to try loading a disk. I'm unsure whether or not to clean the disk first or whether to rely on it having been safe in its plastic bag all these years. I think I'll dismantle and clean it just to be sure for the sake of the heads. That'll be today's job. I'm still recovering from the strain of lifting the unit onto my workbench.

I hope the heads are OK. The unit has had some knocking about, and with the batteries shot the heads had bounced off the duckbill and rattled back and forth a bit. We'll see!
 
I also have an RK8E and an RK05 to restore.
What did you use for replacement batteries for the head retract?

It is common for the rubber elbow that connects the HEPA filter to the cartridge to dry out and crumble, so be careful with it.

With the RP06 you can remove the drive number block and spin up the drive. The heads will not move without a drive number. I run the drive like this for about 10 minutes to purge the drive before I let the heads go onto the pack.
Maybe something similar can be done with the RK05?

The RP06 manual shows how to disconnect the voice coil and to manually move the heads onto the platters while listening for unusual noises.
Maybe you can do this with the RK05?
 
I just used common or garden AA- size NiMh batteries. The originals are NiCd and charged on a permanent trickle. The AA is quite a bit longer than the originals but same diameter and plenty of headroom. I got some tagged ones and soldered them together (same as original pack). They hold the head carriage fine. (You can feel the force as you try to manually load the heads.)

I didn't fancy the rubber elbow shedding crud into the drive so I took it out and gave it a good massage to check it was still flexible. Seems OK and I gave it a good rub to remove surface deterioration.

The RK05 has a switch which disables head loading so easy to run up without the heads suddenly flying in. I plan to write a short routine to step the heads in slowly (assuming the control electronics are all OK) with my finger on the Load switch ready in case of funny noises.

Actually as a bit of a disaster the first disk cartridge I tried to spin up fell apart. The steel plate on the bottom which attracts to the spindle came unglued from the rest of the hub and the disk wobbled around a lot before I could spin down. I think that luckily the duckbill design has kept it from striking the heads!
 
I went through the same restoration procedure with an RP06 at home. I was very careful when I pushed the heads (lots of them) onto the platters (lots of them too) the first time. Unfortunately there is a head loading ramp, and once I pushed the heads a little they quickly slid down the ramp and onto the platters. It worked fine and didn't make any bad noises. I ran the drive for about 10 minutes, pulled the pack, and checked the heads. Several of them were dirty, so I repeated the process. After several cycles the heads remained clean.

I think that the RICM has an RK05 pack cleaner so I will try that on my packs, and on the pack for the PDP-12.
 
Clean the platters by hand, unless you can convince yourself that the pack cleaner is actually cleaner than the packs.

Since the packs haven't been used in quite a while, the inside of the packs probably needs to be cleaned as well as the disk surface. One of our volunteers suggested mild detergent and deionized filtered water to clean the inside of the pack and the media. Then use alcohol to displace the water on the media, and blow dry. We could connect a fan to a HEPA filter to make a clean air source to dry the media.

The pack cleaner has been sitting for years, so it needs to be disassembled and cleaned before it can be used. We have a bunch of new cleaning pads still sealed in plastic bags. If the cleaning pads have not deteriorated they should be OK. I have a bottle of reagent grade alcohol, but that may not be best for cleaning magnetic media. Maybe Freon?
 
How have the packs been kept? The ones that I have were last used approximately 30 years ago and I have opened one up today to find it (so far as the eye can tell) quite spotless. I gave it a clean anyway before putting it back together. These have all been stored on edge in the original polythene 'Texwipe' zipped bags.

I tried easing the heads slowly across the width of the disk listening for funny noises. Nothing much, just the sort of quiet singing sound that I remember from years ago. All seemed good.

So on a bit of a whim I tried booting from it. Surprise surprise - up it came just fine. Looks like a mid-70s version of OS/8 but I haven't explored it in any detail. I could run both Basic and F4 just fine. Well well :) ! I haven't tried any other disks yet.

So far as cleaning goes, I used alcohol. The DEC literature recommends alcohol wipes.

I have 1 minor problem remaining. A couple of components on the Relay Board look shot but I don't really know what they are. They look like axial capacitors but on the parts list they are called suppressors. On the RK05 Relay Board schematic they are D2 and D3 - yellow, cylindrical, about an inch and a half long and half an inch diameter. The ends have opened up rather like a blown capacitor. They are wired across the relay coils and things seem to be working OK but I don't want to find a relay driver suddenly blowing. Schematic symbol is like 2 opposing diodes superimposed on top of one another.
 
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"They are wired across the relay coils and things seem to be working OK but I don't want to find a relay driver suddenly blowing."

Western Electric/Lucent gear tends to have a "contact protection network" across the windings of most relays. They consist of a typical insulator/foil capacitor wound around a typical carbon film resistor. Then the axial leads of both are soldered together putting them electrically in parallel. Just like in the old days with point controlled car ignition systems, when something opens a circuit with an inductor in it like a coil or in this case a relay winding, you're going to get an arc somewhere if you don't to something to "suppress" it. In the car ignition case if your "condenser" is bad or missing the distributor contact points won't last long. Two opposing diodes are a new one for me but I guess they're doing the same thing in some fashion, suppressing a current spike or an arc somewhere in the relay driver circuit.
 
They are a thyristor/thyractor. Like a TSV: https://en.wikipedia.org/wiki/Transient-voltage-suppression_diode

It looks like they are used in the Teletype reader control in DEC systems, DEC TU56 tape controller, and DEC Type-30 display..

GE 6RS20SP4B4. Datasheet: http://www.datasheetarchive.com/dlmain/Datasheets-X/Document-242.pdf
Military/High-Rel : N
Minimum Operating Temp (шC) :
Maximum Operating Temp (шC) :
V(BR) Nom.(V)Rev.Break.Voltage : 170
@I(R) (A) (Test Condition) : 1.2m
V(RWM) (V) Work.Pk.Rev.Voltage :
I(PPM) Max.(A)Pk.Pulse Current : 20
V(C) Nom. (V) Clamping Voltage :
@I(PP) (A) (Test Condition) :
t(resp) Max.(s) Response Time :
Semiconductor Material : Selenium
Package Style : Axial-35
Mounting Style : T
 
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I hadn't meant to imply that it was (or wasn't) a diode device, just that the symbol looks like that. It's drawn as 2 parallel lines with the diagonally opposite ends joined by other lines - presumably a standard symbol of some sort that I've not seen before.

It's really too large to make me think it's a semiconductor. (I'm not even sure that TVSs were around in the 70s). Also the ends seem to have 'popped' a bit which wouldn't be likely with a diode just from ageing. I tend to agree with DDS that it's probably a snubber of some sort but how that would be better, or less expensive, than a simple catching diode eludes me.
 
Thanks Michael.

No obvious mechanism why a selenium stack would 'pop' due to ageing so I think POSSIBLY it's just the packaging that has deteriorated slightly. I think that selenium stacks can go high resistance with age but they don't distort physically. I will put a 'scope across them today and see whether they are catching the relay coil backlash satisfactorily or not. If there's a problem I think the easiest thing to do is to put a decent diode in parallel.

I wonder why DEC didn't use a silicon diode in the first place, I was certainly using them for that purpose in the early '70s. Maybe they just erred on the side of caution by using a component they were familiar with for the job?
 
It looks like D2 and D3 are across the Spindle Motor and the Blower Motor, not the relay coils. That might have something to do with the size.

The data sheet has some of the specifications so you should be able to pick a TVS to replace it.
 
Thanks for pointing that out Michael. I must be getting older more quickly than I'd thought ;).

So I've checked what's happening across them and it looks as though they are still clipping off the overshoot so I'm assuming that they are still OK and their packaging has just aged poorly. It's just a non-functional casing by its looks.

I had 6 disks to begin with. One disintegrated and I'll look at it later. I've cleaned the remainder (though they seemed fine to my eye) and I can read 4 of them fine. The last one has a lot of bad files on the A side although the B side seems intact so I think it is corrupt rather than damaged. All 5 boot!

So while I'm on a bit of a roll I've humped my other RK05 onto the bench for a poke around. This might be a bit more challenging as its in poorer condition. I never fail to be surprised by how well the old DEC kit survives years of terrible treatment and can still be functional.
 
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Only one of them has the heads. :-(

Thats unfortunate, you might struggle to replace so many.

I wonder what happened to them all. Years ago I used RK05s very regularly, all day every day for test program development, and I can't remember ever losing either a disk pack or a head. Very reliable units IME.
 
I have one RK pack in my collection that stowed away in a purchase of RL02 packs. If I recall my count of the sector notches correctly, it's a PDP-11 pack. I don't have a matching drive yet.
 
Thats unfortunate, you might struggle to replace so many.

I wonder what happened to them all. Years ago I used RK05s very regularly, all day every day for test program development, and I can't remember ever losing either a disk pack or a head. Very reliable units IME.

I can remember leaving a PDP-11 system with RK05 disks left running on a Friday, and when we came in Monday morning the drive window was covered in a fine light brown dust and the drive was emanating a rhythmic high pitched squeal. We powered it off and opened up RK05 and pulled the cartridge. Covered in brown dust. We removed the white plastic shield from the pack and it had a nice circular ring scraped down to the bare aluminum platter. Can you say head crash. Needless to say the drive heads were toast as well.

Since we were DEC engineering we called IHFS (in house field service) who repaired these systems and they took one look and brought us a replacement Rk05 drive unit. They chastised us (appropriately) for (probably) letting the pack/drive go without cleaning (probably for a couple years or more, since initial setup). Basically as internal engineering we never had IHFS do any routine maintenance on systems. We only called them when it failed and was unusable.

Software lab systems usually were on an IHFS monthly maintenance contract so would get routine checks and cleaning every month. Hardware engineering was too cheap to do that, they only contracted with IHFS on a system repair call.

Don

PS someday I'll write a post about the PDP systems available in the ML5-5 (building 5 for sure, my recollection is the 5th floor) software development lab. When I did diagnostic development I would sign up for dedicated time on a 4MB PDP-11/70 with RP06 disks to run standalone RT-11 for hours on an end. This was in 1978.
 
Oh dear! Pride and an Haughty Spirit and all these good biblical sayings! or something like that. Anyway after a considerable amount of struggling I got RK05#1 mounted in the cabinet under the 8/e, switched it all on and lo and behold the disk door doesn't unlock, so something seems to have failed somewhere. The logic for the door unlock is pretty simple so I'm hoping it's nothing much but it'll be another grunt session if I have to get it back onto the bench. To save a bit of sweat I mounted the RK05 in the 2nd bottom position in the cabinet so it's inconveniently low down to work on in situ. (Nevertheless I'll have a go - I'm too old to hump these hundredweight bits of kit around too often!)

:( :( :(
 
I put my RK05 below the 8/e also. The door does unlock when it is powered on. I haven't tried holding the pack-detect microswitch to see if the blower and spindle motor will go on.
 
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