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Classic / Classic II ATX power conversion.


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Hello, I am new here. Figured I'd jump in with something outrageous.

 

Preamble:

 

I've acquired a non working Classic and a Classic II with early (EAB) and late (LAB) analogue boards respectively. I have recapped both ABs and LBs. 

The LAB would blow the fuse immediately, eventually 'solved' by borrowing the QP2/IRFBC40 from EAB unfortunately this still didn't result in a booting LB (see below).

The EAB would under-voltage, including +31V DC rail (approx 20V unloaded, 16V loaded). This results in a dim and wobbly display.

With the EAB the C1LB would checkerboard, and the C2LB would white screen.

Once revived the LAB showed stable voltages, but would still checkerboard on C1LB, and white screen on C2LB. By this time I had already established the the C2LB could boot successfully with good power so I am at a loss as to why this is.

 

Aaaannyway...

 

How do I know the C2LB is good? well I removed the power wires from the EAB and soldered ATX pins on the end and inserted them carefully into the correct voltage rails of a spare PC power supply, this left the AB to power the local electronics + the CRT, but the LB was now powered from ATX.
Although the screen was still dim and wobbly, I was able to see C2LB boot (yay), unfortunately I still got a checkerboard C1LB (boo).

 

So what next?

 

Well I reinserted the power wires back into the EAB, but then tapped in a molex HDD connector for 12V and 5V, leaving the -12V on a wire to plug into the ATX power connector. This meant the EAB was now 'receiving' power from the ATX board on those rails as well as the LB. I then took a DC-DC Boost converter and tuned it as close to 31V as possible (actually it maxed out at 29V) and soldered this onto the output pin of IP2/LM317.

 

Guess what? It works! I now have CRT power provided by the ATX supply, and it's bright and stable, and the C2LB boots like a champ.

 

Sadly the C1LB still checkerboards, this is a shame because it's the one I really want to see working. But at least I think I can be pretty certain the fault is with the LB not the PSU.

 

Oh and another thing! The first 7 rows of the ATX power connector are keyed in a compatible way with the 14pin connector on the LBs. Only the latch doesn't line up so a spot of hot glue may be required to keep them in place. Taking an ATX power extension cable and cutting off the excess contacts would happily plug in between the AB and LB.

 

What does this mean?

 

I figure if I picked up a couple of ATX power extensions, I could make up a harness that could simply be inserted between the AB and LB with a seperate connector to take power from an ATX supply.

This would provide +12, +5 and -12V to both boards as required.

 

The only hardware modification required would be to inject +31VDC into the AB on the output of IP2/LM317, this would be provided via a suitable (common negative) DC-DC boost converter powered off the ATX 12V.

 

To my eye the circuitry on the AB looks like it should be pretty happy with being fed power the 'wrong' way. Except maybe IP3/LM79L12 which could do with a bypass diode like IP2 and IP4 both have? (but pointing the other way, cos negative), although I don't believe this gets used anywhere on the AB so the harness could be designed not to pass this back to the AB.

 

Guess I better top my tall story off with a picture, turns out it's not that easy to take a photo that shows both the screen and the lack of power cable into the back of the AB, but here goes. The white shield helps show the lack of power into the AB. ATX power wires are soldered onto the back of the AB opposite the loom which runs to the LB.

 

I'll post updates here when/if I make some progress.

 

Classic2ATX.thumb.jpg.aa4e3a76b87ab72d72be4d14fcbd48ba.jpg

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Here's a couple of pictures that show what's going on better.

I've ordered cables and a different dc-dc to make an adapter harness.

Turns out some Lenovos use 14p molex, and ATX adapters are readily available, so I'll just move pins around and splice wires accordingly.

 

IMG_20200817_104030__01.thumb.jpg.85ec631ab5ff553cf69dd84d2d73207a.jpg

 

IMG_20200817_104148__01.thumb.jpg.4a343ac3d86732109fd9ebd2113da9e4.jpg

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19 hours ago, bibilit said:

interesting, what is the thick white wire ?

Hi, the thick red and white wires are the output from the DC-DC boost converter soldered into the yellow plug on the edge of the last picture..

 

The white one is negative/ground, but as the boost converter has common negative it is technically surplus to requirements.

The red one is +29VDC injected into the output of the LM317.

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  • 4 months later...

So... after moving house and finally reaching the end of the year, I finally had some time to look at this again.

 

But a catchup story first.. I did order a bunch of components and try to fix the ABs, I can't remember where I got to with the C1/EAB but the C2/LAB I made some progress after swapping in new optocoupler, voltage reference and barrier diode. It was looking okay for a bit, but then started outputting low voltage again. As I was poking around the regulator driver IC I accidentally bridged two pins and saw a small spark and it blew the fuse!

I replaced the fuse, and turned it back on BANG! big ass spark, plunged into darkness as the breaker/RCD to the shed killed the power.

 

Came back and found the RP2 had puked all over the AB, it looked like the QP2 had gone properly dead-short. My replacement fuse was the correct current rating, but I'm guessing not the right type to save the board.

 

So.. I figured there was probably still a reasonable chance the low-voltage and CRT stuff on the board would still be okay, which was easy enough to test by hot-wiring it into the ATX supply as above. Everything still looked okay so I figured I'd go full butcher-spec and attempt to rip out all the AC and regulator circuitry and see if I can reduce it to a pure CRT+Audio board.

 

IMG_20200831_151406.thumb.jpg.dae6e59a436553d97f5489e88e280761.jpg 

 

IMG_20200831_160749.thumb.jpg.a348bd56a22ea18232d5a1368589f74f.jpg

 

IMG_20200831_160800.thumb.jpg.164085722bf1833b25c2f264ec5b974c.jpg

 

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So it stayed like that until basically two days ago when I found some time to look into it again.

 

In the mean time I ordered some parts, a "PicoATX" PSU that takes an input of 16-28V or whatever, I don't like the look of the 12V input ones, as I'm guessing they just pass the 12V through which sounds risky to me. I got a smaller DC-DC boost converter that could generate up to 36V from 12V input to drive the CRT.

 

I also ordered a few ATX adapter cables, and some pin removal tools. My original intention was to build an adapter, but In the end I just hacked up the harness that came with the PSU as I figured it was moving into its new forever home at this point. I may consider doing an adapter on the EAB from the C1.

 

So without really testing stuff along the way, I hacked into the power harness that came with the PSU, and soldered them into pads left where I'd removed components from the board. I drilled a few slightly larger holes in the PCB to take a few extra ground wires as I figured I may as well keep all of the ones provided by the harness there.

 

With the boost converter I decided to send 36V to the input of the LM317 (instead of 30V to the output like in my previous tests), on the late AB at least, the 317 forms part of a soft-start circuit which I figured could stay there.

 

I also wired the original power switch in the ATX power pins, although I think I might move this to the power input at some point (because always-on blue LED).

 

And, it works!

 

Got out the hot glue gun and mounted the boost converter directly to the face of the PCB, and the pATX PSU at right angles along the bottom.

 

It's running from a 24V DC power supply, but I secretly want to put the magsafe connector from an old Macbook in the place of the old AC inlet. First I need to do some power consumption tests to see if it will be happy on a 65W magsafe PSU.

 

This is one beat-up Classic II, I can't decide if I like it like this, or if I should swap it into the Classic I chassis which is in much better condition.

IMG_20201221_182410.thumb.jpg.fb465f59cc850ad7f502da406a5c11c8.jpg

 

IMG_20201221_183200.thumb.jpg.2228b7e3857f4885f67071d2136e5b85.jpg

 

IMG_20201221_183907.thumb.jpg.7e2ef6e41d8cce4b60ddd7584ea5d113.jpg

 

IMG_20201221_183846.thumb.jpg.88f335044540e195380b1606bcd2b500.jpg

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Thanks, I see you're also attempting to revive an analog board. Good luck with that.

I had similar symptoms as you describe in your thread, that is until I blew things up.

 

These are the parts I used to get to this point.

 

pATX Power supply

https://www.aliexpress.com/item/32888405080.html
DC-DC Boost converter

https://www.aliexpress.com/item/4000848001858.html

 

I also used these pin extractors to remove the wires I didn't need, although I don't recommend these specific tools. I had to sharpen the inside of the fork to get it to insert fully and release the ATX pins, even then I damaged a few pulling them out.

https://www.aliexpress.com/item/32906393668.html

 

I think I'd still like to make a non-destructive ATX adapter harness, which I may try with the C1/EAB. The only modification required for this to work is to send ~36V to the cathode of DP5, this could even be done with a test hook (all the other voltages and grounds would go through the 14pin molex connector).

 

I actually ordered a couple of 24p - 14p adapters before the pATX PSU, but haven't used them yet. The plan was to cut down one of the 24p sockets to 14p then rearrange and splice wires to build a Y-cable which injects the required voltages.

https://www.aliexpress.com/item/33024312619.html

 

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  • 3 weeks later...
On 12/22/2020 at 8:55 PM, mogs said:

So... after moving house and finally reaching the end of the year, I finally had some time to look at this again.

 

But a catchup story first.. I did order a bunch of components and try to fix the ABs, I can't remember where I got to with the C1/EAB but the C2/LAB I made some progress after swapping in new optocoupler, voltage reference and barrier diode. It was looking okay for a bit, but then started outputting low voltage again. As I was poking around the regulator driver IC I accidentally bridged two pins and saw a small spark and it blew the fuse!

I replaced the fuse, and turned it back on BANG! big ass spark, plunged into darkness as the breaker/RCD to the shed killed the power.

 

Came back and found the RP2 had puked all over the AB, it looked like the QP2 had gone properly dead-short. My replacement fuse was the correct current rating, but I'm guessing not the right type to save the board.

 

So.. I figured there was probably still a reasonable chance the low-voltage and CRT stuff on the board would still be okay, which was easy enough to test by hot-wiring it into the ATX supply as above. Everything still looked okay so I figured I'd go full butcher-spec and attempt to rip out all the AC and regulator circuitry and see if I can reduce it to a pure CRT+Audio board.

 

 

 

IMG_20200831_160749.thumb.jpg.a348bd56a22ea18232d5a1368589f74f.jpg

 

 

 

Hi @mogs

in this picture you left all the capacitors close to the speaker, but in a following one some have been removed (e.g. Cp2 CP36..) and also the inductance. Apparently IP3 has been removed as well because from the picture I can not tell, can you please list which components you removed or you left? Specifically the part on the left obscured by the cabling.

 

What about PP1, DP14, DP3 and Dp4, cant' they be removed as well? To my understanding those are to feed to optocoupler.

 

thanks

 

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Hi again.

 

Yes you are correct, I did remove additional components to make room for the PSU which was just a little too long to fit along the bottom of the PCB with those in place.

 

My original intention was to leave the inductors and capacitors on each power rail, but I decided the PSU probably had sufficient capacitance to keep things stable.

 

If I open it up again I'll try to take some clearer photos, but for now I can tell you what I remember.

 

Grey: +36V into cathode of where DP5 was.

Yellow: +12V into where lower pin of LP5 was.

Red: +5V into where LHS of LP4 was.

Blue: -12 into where output of IP3 was.

 

All components prior to the above removed components were also removed (right had side of PCB, left hand side of schematic).

 

The grounds all go into the negative side of the capacitors I've removed, I also drilled a few additional holes for all the remaining ground wires from the PSU.

 

If space for your PSU is not a concern, you might consider just removing the diodes on each rail (DP5, DP6, DP7, DP8) and inject your power there, leaving the inductors and capacitors in place. This should theoretically offer some additional filtering.

 

I did consider removing the other components you mention for the adjustment, and looking at the circuit they do appear to be live so it might be a good plan.

I was a little shy about accidentally removing something not related to the PSU, but for 'purity' sake maybe I should give that a go.

 

 

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4 hours ago, mogs said:

If space for your PSU is not a concern, you might consider just removing the diodes on each rail (DP5, DP6, DP7, DP8) and inject your power there, leaving the inductors and capacitors in place.

 

Except the -12V goes through a regulator which wouldn't work, so that would still need to go in place of IP3. 

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