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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 26th Mar 2021, 7:10 pm   #21
Buzby123
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Default Re: GRID PSU, definitely 'Not Working' !

Yes, I read yesterday on some GRID forum that these laptops only work with specific Connor HDDs.

I'm not too bothered at the moment, I've put the 1530 back in the attic !.
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Old 26th Mar 2021, 9:49 pm   #22
ortek_service
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Default Re: GRID PSU, definitely 'Not Working' !

I seem to recall having to get a specific Connor? IDE drive to use in a docking station unit on an old 1992 Olivetti Walkstation Laptop, which I think only had a few types supported by the BIOS.

And that early IBM AT etc. desktop PC's only had around 6 or 12 types built-in, with later ones having upto 47? So you sometimes had to choose the closest match, before they eventually let you enter all the heads, cylinders, sectors parameters, and had to ensure you used the same setting once you formatted it.
When IDE drives superseded MFM/RLL ones, their controllers re-mapped the physical parameters onto ones supported by common PC's, before auto-detection became common place (which in the early days wasn't dynamic at reset, and you had to go into the BIOS setup and chose it to auto-set parameters).

So it could be a lot more of a pain to get a HDD working back then - especially with laptops, that often had much more restricted BIOS settings.


Some really old PC's also needed you to run a setup program from Disk (Presumably ones, that you couldn't change FDD settings on!)
And the procedure for entering internal BIOS setup has varied quite a bit, often being holding down Delete, F1 or F2, but sometime Esc or possibly having to do Ctrl+Alt+(another key like Esc)

- So a few to try, when you next play with it
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Old 27th Mar 2021, 2:32 pm   #23
philip_s
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Default Re: GRID PSU, definitely 'Not Working' !

Well done for fixing the DS1287 -- I've never had any luck with the drill-and-replace-battery method. Sorry to hear you've got a dead hard disk :-(

When you do come back to this, the PSU component values are:
Code:
C5 200V 220uF 105C
C6 200V 220uF 105C
C7 25V 105uF 85C
Q1 Motorola IRF840
Q2 Motorola IRF840
The inductor you're missing is covered with resin so I wasn't able to get a good look at it, but I have attached a photo of it in case that's helpful.

Regarding the BIOS settings, there is no key combination to get into a setup screen. The 15xx series use a heavily modified Phoenix BIOS that predates built-in setup screens. Normally you would have to load a program from floppy disk to modify the BIOS settings, but in an attempt to make things easier for users GRiD made the BIOS self-configuring. This is the reason the stock BIOS only works with certain Connor drives.

The PCB on the drive bay that the floppy/hard disks plug into has certain pins strapped high/low so the BIOS can identify the type of drives that could be present. There are 16 possibilities here; the ones I know about are:
  • 0 Drive bay not present
  • 1 Single floppy
  • 2 Dual floppies
  • 3 Single floppy, XT-compatible HD (subtypes 1/2/3)
  • 4 Full-height XT-compatible HD (subtype ?)
  • 5 Full-height AT-compatible HD (subtype 4)
  • 7 Full-height AT-compatible (autodetect)
  • 9 Single floppy, AT-compatible HD (autodetect)

The 'subtype' codes are used to index into a table of 47 hard disk types (with a special case for the full-height 100MB Connor drive whose parameters are located elsewhere). The entries marked 'autodetect' use the ATA Identify Drive command to read out the model number -- this is where the BIOS is tied to specific Connor models: CP3022, CP3024, CP344, CP3044, CP3042, and CP3104.

I have a long-term project to produce a commented disassembly of the 1520 BIOS that assembles byte-identical to the original ROM. The 1530 BIOS is next on my list once that's complete. Hopefully it can be modified to support more modern drives fairly simply...

The LCD/plasma screen confusion some sites have is probably because both were available. I have machines with both the yellow-on-blue LCD and the orange plasma (apparently available in 640x200 'low power' and 640x400). These were CGA resolution, upscaled to match the panel's native resolution. Service manuals reference a VGA option, but I've never seen one in the wild. One thing to watch out for if you need to repair the DC-DC converter module at the back of the machine is that there are different modules for each display type with incompatible output voltages -- so don't swap them between machines without checking that
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Old 28th Mar 2021, 11:46 pm   #24
Buzby123
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Default Re: GRID PSU, definitely 'Not Working' !

Hi Phil,

Thankyou very much for the details. It looks like no problem getting the transistors and caps, but that inductor might take a bit more effort.

It looks like it's got about 20 turns on both a primary and a secondary, so it'a 1:1 ratio. ( There are 4 holes in the PCB I think are for a pri/sec arrangement. ). Should be quite easy to wind one, if I can get a suitable toroid.

I'm also going to replace the X2 caps, as one of them is falling to pieces.

Regarding the computer itself, my immediate problem is why the floppy isn't working. At boot time the LED on the drive lights for a few seconds, but there is no disk noise, even with a disk inserted.

I really want to get this machine working, but it will be a couple of weeks before I can work on it again.

Cheers,

Buzby
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Old 29th Mar 2021, 1:06 am   #25
ortek_service
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Default Re: GRID PSU, definitely 'Not Working' !

It's a shame the 'Inductor' actually appears to be a bifilar-wound torroid transformer, so I guess it may be part of a feedback-sensing circuit and not just supply filter inductor that could probably be bypassed for testing etc.

And so it's probably the only one of its type in there, and so there isn't another that could be measured. Although the same core type may have been used elsewhere, as identifying the exact one used can be difficult.
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Old 29th Mar 2021, 9:52 am   #26
duncanlowe
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Default Re: GRID PSU, definitely 'Not Working' !

Quote:
Originally Posted by ortek_service View Post
It's a shame the 'Inductor' actually appears to be a bifilar-wound torroid transformer, so I guess it may be part of a feedback-sensing circuit and not just supply filter inductor that could probably be bypassed for testing etc.
It may still be a filter. I have seen a similar technique in another field for isolating RF from power current. If you use a simple single wound inductor, then the power current (In the case I know DC, but my guess is that 50Hz would be low enough to behave the same) then the magnetic core saturates and doesn't do the job. You can get around this by doing a bifilar inductor so the DC or low frequency components cancel each other out and the core doesn't saturate so works properly as an RF filter. There was even a patent for the particular DC based use I came accross.
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Old 29th Mar 2021, 10:23 am   #27
Buzby123
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Default Re: GRID PSU, definitely 'Not Working' !

I couldn't resist having another look, so here are some close-up pictures of the board.

It definitely looks like L5 was a transformer of some kind.
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Old 29th Mar 2021, 12:32 pm   #28
ortek_service
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Default Re: GRID PSU, definitely 'Not Working' !

The wire looked a bit thin on the original one, to be used for a DC output-filter, and its position on the board would also indicate that it isn't being used for this.

It looks like it's associated with the controller board sub-panel, and I'm thinking it could be used to drive the 2 (missing) Power MOSFET's - maybe converting single-ended to differential outputs (although it's difficult to follow the double-sided PCB tracking on photos, , to see if it does connect to these).

And if the original MOSFET's went s/c, they could have damaged a gate-drive transformer, so might explain why it was removed (and possible the HT reservoir capacitors for access, or maybe these had failed and caused other damage with excess-ripple).
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Old 1st Apr 2021, 11:16 am   #29
philip_s
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Default Re: GRID PSU, definitely 'Not Working' !

Quote:
Originally Posted by Buzby123 View Post
Regarding the computer itself, my immediate problem is why the floppy isn't working. At boot time the LED on the drive lights for a few seconds, but there is no disk noise, even with a disk inserted.
I have seen this behaviour before on one of my 1520s with a dead HD. I waited until the floppy light had gone out, then performed a soft reboot with ctrl+alt+del. The computer then sat at a blank screen for several minutes before finally booting from the floppy. Probably some long timeout in the HD init code that's inside another loop
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Old 1st Apr 2021, 5:15 pm   #30
Buzby123
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Default Re: GRID PSU, definitely 'Not Working' !

Hi Phil,

I will try this next time I get the machine out. When I did it last time I'm not sure if I left the disk in the floppy drive.

The disk I'm trying is a standard formatted DOS 6.22 boot disk, should this work ?.

Cheers,

Buzby
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