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by jonb
Sat Mar 23, 2019 4:43 pm
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 31
Views: 346

Re: Mystery Zener Diode

John, it's a retro computer. :D

Anyway, here are some horrid demo videos.

https://youtu.be/UTTQptrt3Nc

https://youtu.be/8hshdu2_P7Q

Awful... :oops:
by jonb
Sat Mar 23, 2019 3:26 pm
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 31
Views: 346

Re: Mystery Zener Diode

Thanks, but remember, it's a collaborative effort, so thank you to all who advised me on this!
by jonb
Sat Mar 23, 2019 11:16 am
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 31
Views: 346

Re: Mystery Zener Diode

With the arrival this morning of the 150 Ohm resistor, new 10uf non polarised capacitor (which is 1/3rd the physical size of the old one, despite being a higher voltage rating) and a BU406, I had a quick solder session. And so... IMG_1202.JPG I probably need to fiddle with the trimmers a bit (have a...
by jonb
Sat Mar 23, 2019 10:03 am
Forum: other vintage computer hardware, software and games
Topic: Exidy Sorcerer
Replies: 43
Views: 3256

Re: Exidy Sorcerer

Hi Paul You're right, I think, except that on some drives it's necessary to set a jumper for hard sectored operation - the Shugart 850 is an example. At this time, it is evident that the boot ROM that lives in the drive unit is not being accessed properly by the Sorcerer. The two are connected with ...
by jonb
Fri Mar 22, 2019 6:54 pm
Forum: other vintage computer hardware, software and games
Topic: Megastor 8" drive unit
Replies: 38
Views: 748

Re: Megastor 8" drive unit

Some crappy videos showing the drives in action.

Part 1: https://youtu.be/CNrnfQ3Y6LE
Part 2: https://youtu.be/g8RkajkR1Hk
Part 3: https://youtu.be/-0I8sCGYPCw

Cheers
JonB
by jonb
Fri Mar 22, 2019 6:16 pm
Forum: other vintage computer hardware, software and games
Topic: '80s computer geeks' pictures.....
Replies: 19
Views: 369

Re: '80s computer geeks' pictures.....

Actually, 32 x 8MB (with a slave drive), but you can only access 16 at once (A: to P: inclusive). Any more than that is just greedy. On the TRS 80 it is configurable, so you can choose how much TPA you give to the driver, balancing number of accessible drives with memory usage. (The driver needs 257...
by jonb
Fri Mar 22, 2019 6:00 pm
Forum: other vintage computer hardware, software and games
Topic: '80s computer geeks' pictures.....
Replies: 19
Views: 369

Re: '80s computer geeks' pictures.....

Of course, you probably noticed I have an affinity for CP/M computers... which I cannot explain. I have a couple of Beebs here but never use them (or the Atom, Electron, Spectrum, etc, etc). I seem to be doing stuff with CP/M and hardware that predates the Beeb all the time. For that reason I'd hap...
by jonb
Fri Mar 22, 2019 5:28 pm
Forum: other vintage computer hardware, software and games
Topic: '80s computer geeks' pictures.....
Replies: 19
Views: 369

Re: '80s computer geeks' pictures.....

Ah now, Exidy Sorcerer... I have a drive for mine but it's broken (hard sectored too). Sorcerer can't read the boot ROM, or something.
by jonb
Fri Mar 22, 2019 2:57 pm
Forum: other vintage computer hardware, software and games
Topic: Megastor 8" drive unit
Replies: 38
Views: 748

Re: Megastor 8" drive unit

Another thing I noticed was that the BASF drives are fairly quiet. Much less clunky than the Shugarts. In fact, the Megastor chassis fan is the noisiest part of the whole rig. So, for the benefit of Kazzie, I will do some videos of the BASF and Shugart drives working. Should be fun.. Many thanks, I...
by jonb
Fri Mar 22, 2019 10:45 am
Forum: other vintage computer hardware, software and games
Topic: Megastor 8" drive unit
Replies: 38
Views: 748

Re: Megastor 8" drive unit

A brief interlude. One of the mysteries I have had to contend with while restoring the BASF drives is the odd behaviour of my spare Shugart 850 drive. I used it to boot the TRS-80, as its internal drive is jumpered as DS2 so cannot be booted from (it's all to do with using an HXC as the boot drive)....
by jonb
Fri Mar 22, 2019 10:34 am
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 31
Views: 346

Re: Mystery Zener Diode

Meanwhile, I pulled the MPSU05 (Q413) and tested it. It's OK (a relief, as they are getting priced at £10 on a certain online auction site).
by jonb
Fri Mar 22, 2019 10:33 am
Forum: other vintage computer hardware, software and games
Topic: '80s computer geeks' pictures.....
Replies: 19
Views: 369

Re: '80s computer geeks' pictures.....

That's true, John. I suppose that, if I were trying to prepare youngsters for a career in computing in the '80s, I'd still choose the 380Z because it ran CP/M, which was the prevalent OS for businesses at the time. Very expensive, though! My local Tech College (where I sat my A-Levels, including Com...
by jonb
Fri Mar 22, 2019 9:40 am
Forum: other vintage computer hardware, software and games
Topic: '80s computer geeks' pictures.....
Replies: 19
Views: 369

Re: '80s computer geeks' pictures.....

It was a piece of junk really, which was slaughtered by the BBC Micro. I was still impressed with it, when I was 5. That's an interesting point of view. It was a CP/M machine (when sold with disks) and used rack mounted cards (but no motherboard). Compared to the Beeb it was indeed primitive, but t...
by jonb
Fri Mar 22, 2019 8:05 am
Forum: other vintage computer hardware, software and games
Topic: Megastor 8" drive unit
Replies: 38
Views: 748

Re: Megastor 8" drive unit

No, I think it needs a capacitor across its contacts.
by jonb
Thu Mar 21, 2019 6:05 pm
Forum: other vintage computer hardware, software and games
Topic: Megastor 8" drive unit
Replies: 38
Views: 748

Re: Megastor 8" drive unit

A picture of the 8" drive test rig.

8 drive test rig.jpg

..and a bit of retrocomputing pr0n..

TRS-80 Model II goodness.jpg
Juicy TRS-80 Model II with amber screen filter and Shugart SA801 8" floppy drive
8)
by jonb
Thu Mar 21, 2019 5:58 pm
Forum: other vintage computer hardware, software and games
Topic: Megastor 8" drive unit
Replies: 38
Views: 748

Re: Megastor 8" drive unit

Stage 2 Fit known good ICs (test old ones by swapping out the same ICs on Drive 1 and seeing if it still works). Drive 2 board Stage 2.jpg Surprising how many ICs on Drive 2 actually survived. It's still missing a TIP32C transistor from its stepper motor output stage (swiped to get Drive 1 going) -...
by jonb
Thu Mar 21, 2019 5:03 pm
Forum: other vintage computer hardware, software and games
Topic: Megastor 8" drive unit
Replies: 38
Views: 748

Re: Megastor 8" drive unit

Stage 1

Remove all the old ICs and fit IC sockets.

Drive 2 board.jpg
Drive 2's board prepped up

Got a sore back now! :)
by jonb
Thu Mar 21, 2019 4:45 pm
Forum: other vintage computer hardware, software and games
Topic: Superbrain #3 : The Superbrain II board
Replies: 76
Views: 1751

Re: Superbrain #3 : The Superbrain II board

There is nothing similar. It's my favourite CP/M machine. But you might consider: A TRS-80 Model II (with 8" floppy drive) and Lifeboat, Aton or Pickes & Trout CP/M (I have one) A TRS-80 Model IV with CP/M A TRS-80 Model IVP (portable), again with CP/M Northstar Advantage Kaypro 2 (but has 9" screen...
by jonb
Thu Mar 21, 2019 1:43 pm
Forum: other vintage computer hardware, software and games
Topic: Megastor 8" drive unit
Replies: 38
Views: 748

Re: Megastor 8" drive unit

Right, next up is Drive 1. This needs the full monty IC swap as well, but I can test all the ICs I remove now as I have a working drive to substitute chips into for testing. It's desoldering time (again)!
by jonb
Thu Mar 21, 2019 1:41 pm
Forum: other vintage computer hardware, software and games
Topic: Megastor 8" drive unit
Replies: 38
Views: 748

Re: Megastor 8" drive unit

vanpeebles wrote:
Wed Mar 20, 2019 1:13 pm
Would dielectric grease help?
What for?
by jonb
Thu Mar 21, 2019 1:40 pm
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 31
Views: 346

Re: Mystery Zener Diode

Will be if I get it going again. My poor old Superbrain, it needs a hug. It's been through so much surgery.

It's now a waiting game for the parts. meanwhile I will return to the THUNDEROUS 8" MEGASTOR DRIVE UNIT
by jonb
Thu Mar 21, 2019 1:29 pm
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 31
Views: 346

Re: Mystery Zener Diode

And whilst we're at it, R482 is now proven to be 150 Ohm 1/2W: R482 is 150R 1.5w.JPG :D Actually.. whilst we're looking at that resistor, it occurred to me that the tantalum cap might have gone closed circuit (causing the resistor to overheat) but it is healthy (and measuring 4.9uF out of circuit). ...
by jonb
Thu Mar 21, 2019 1:17 pm
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 31
Views: 346

Re: Mystery Zener Diode

Ah ha! Look what I found: http://www.bitsavers.org/pdf/northstar/ ... l_1981.pdf

The Northstar Advantage has the same ELSTON or similar video module and the mystery Zener turns out to be a 1N4747A as expected.

northstar advantage video board.JPG
Gotcha!
by jonb
Thu Mar 21, 2019 12:04 pm
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 31
Views: 346

Re: Mystery Zener Diode

Oh, well spotted Mark! =D> Yes, it goes from position 7 on the edge connector to all the points marked "A" on the diagram. So Q298 may be damaged as it is directly connected to "A". Same with the TDA1120, although the display did work for a short while post fitting the new regulator, so I think ther...
by jonb
Thu Mar 21, 2019 10:59 am
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 31
Views: 346

Re: Mystery Zener Diode

Fortunately I recalled I have some good pictures of the innards of some Superbrains owned by the CCH Museum. In that cache I found this image: CCH SB_JR_ID6747 video board.JPG The resistor is circled. I think this is pretty conclusive proof that it's 150 Ohms - brown-green-brown. You can also see th...
by jonb
Thu Mar 21, 2019 10:35 am
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 31
Views: 346

Re: Mystery Zener Diode

I found another component that looked cooked but isn't on the schematic: R482. It looks like a 1/2 watt carbon resistor and I can read some colours but not the multiplier. I see Brown, Green, [something, possibly black or brown but it's burned at this point]. It measures 184 Ohms (out of circuit) so...
by jonb
Thu Mar 21, 2019 10:11 am
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 31
Views: 346

Re: Mystery Zener Diode

Hi Mark When you talk about the horizontal output stage I assume you're talking about anything to the right of T403. Correct? Can I run this without the tube or LOPT connected and still do meaningful tests? It's quite hard to access once fitted. Also, would you agree the measurements of the BU406 in...
by jonb
Thu Mar 21, 2019 9:16 am
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 31
Views: 346

Re: Mystery Zener Diode

The fuse is not shown on the schematic, but I think each point marked "+12v" is where the white wires are connected. Testing the BU406 NPN transistor using a diode tester according to https://vetco.net/blog/test-a-transistor-with-a-multimeter/2017-05-04-12-25-37-07 B-E .018v (bad) B-C .514v (good) E...
by jonb
Thu Mar 21, 2019 8:46 am
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 31
Views: 346

Re: Mystery Zener Diode

Between the 15v power input and the rest of the board. Annoying that it's not marked on the schematic (you can see some +12v points, these are connected to the inboard side of the fuse by patch wires). Video PCB.jpg Fuse.jpg Zener location.jpg BU406.jpg About the BU406: It has a black layer of carbo...
by jonb
Wed Mar 20, 2019 7:14 pm
Forum: other vintage computer hardware, software and games
Topic: Mystery Zener Diode
Replies: 31
Views: 346

Re: Mystery Zener Diode

Well, I found something not on the schematic. A fuse that looks like a small white resistor - and it is open circuit! I shorted it out, having replaced the zener with a smaller one (having a 3.6v Zener voltage) and fired it up. Bingo, an image, but squashed a little. Then a small pop followed by dar...