Spectravideo X'press SV-738 Mods

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By mxmy

Resident (39)

mxmy's picture

30-06-2018, 07:54

Very happy with my new Spectravideo xpress, but a lot of the information that I find online is very scattered, so I thought I'd do a thread here for general information and questions (and gosh knows I have a lot of questions, haha).

Firstly, I'd be really interested in seeing or hearing about different people's solutions for mounting a 720K drive securely in the chassis. Currently I'm using a a Sony MPF920 that I've modify to function correctly in the xpress by wiring the ready pin to ground and swapping the SMD zero ohm resistor jumper that controls the A & B selection, so that it functions as the first drive. However, my currently solution for getting to drive to sit nicely in the case is currently not great: it's sitting more internally than the original drive, at an angle, and it's only got two, rather than four screws holding it in place.

Also, disassembling and reassembling the unit is taking me a long time. I still haven't figured out exactly how to remove the main board from the bottom of the case... is there a trick to it, eg. any hidden screws I should know about?

Another question I have is: should I ditch all of the metal shielding? It's pretty, but a total pain and I'd rather be rid of it.

Like Nyrikki, I have the, uh, swedish/finnish model, which is very cool, but I'm not sure what key combo the backslash is at. Do I need it for navigating the Nextor DOS2 filesystem? Also, I'm based in the UK, but my powersupply is european which is fine, but the PSU (original) gets very hot and one day will likely fail. Thinking of getting a 16V AC (2amps or more?) laptop power supply unit. Other than not knowing if the plug will fit the socket, is there anything else I should consider? Is it something that I Should Not Do, even?

Thanks in advance, and apologies for all the possibly rather n00bly questions.

And naturally, I'll converting it to an MSX2(+? TURBO?!?).

PS. The PCB material is not great... worse than my Sony HB-75B or Amiga 600, even!

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By CopperPod

Supporter (5)

CopperPod's picture

14-07-2018, 16:55

Hi,

The laptop PSU's are typically DC; the SVI-738 needs 16v AC. All the 16v AC adapters I've checked out on eBay (about 50) were in fact all DC adapters or had too low current throughput. The X'press power plug is 5.5mm x 2.1mm.
I'll be selling replacement PSU's for the X'press on eBay sometime in the future (in a month or two). I'll post it here at msx.org, when they'll be available. Quite pricy, though – sorry; it looks like around maybe £49.95, initially. I can't do large scale production, as I have no idea of size of demand, and can't seem to find the parts I need here in Denmark (at all), so I'm getting parts in China, Australia, Germany, UK etc., and that's just expensive in shipping and import taxes. I'll keep searching for cheaper options, though : )

By CopperPod

Supporter (5)

CopperPod's picture

14-07-2018, 18:56

By alexito

Master (215)

alexito's picture

14-07-2018, 19:40

I have bought one SV738 Xpress I would like to turn on MSX2+ but I'm waiting for more new MODs Infos, because the Info we actually have scare me as hell.

Wink

PS: just the 128KB VRAM mod is done at the moment.

By djh1697

Paragon (1352)

djh1697's picture

15-07-2018, 00:44

I have heard about the Xpress getting upgraded to MSX2, but I personally have no experience in that. I have even heard of one getting upgraded to MSX2+, however, that person is no longer using MSX.

There are instructions on MSX2+ conversion on the excellent MSX Resource centre by Hans Otten.

http://msx.hansotten.com/special-msx-hardware/svi-738-xpress/

By mxmy

Resident (39)

mxmy's picture

19-07-2018, 08:20

@djh1697, The Hans Otten site is fantastic, though I find some of the instructions there very hard to understand...
There's also some great information on This page (Kilroy's Vintage Computers).

So far, I've installed the new VRAM, but I don't at the moment have an eprom programmer, so I'm stuck at the moment using it as an MSX1.

@alexito, I'm almost where you are! I might soon put in a reset switch. I've also added a new, DSDD-compatible floppy drive to the board, which is great, though I still need to make new brackets to hold it in the correct position... Oh, and I've replaced a lot of the capacitors in the system with decent japanese ones (panasonic, ELNA, Rubycon etc.). The only one I left on the power board was the Rubycon 470uf 25V cap.

@copperpod Ahh, no you are right, most of the PSUs on ebay are 16v. A replacement PSU for the 738 sounds awesome! Is it based directly off of the original PSU, or does it use a new design? I'm guessing it's different in some way as the original is 2.5A output.... The biggest problem I have with the original is that is gets very, very hot, which will decrease its lifespan faster. The Power board heatsink and the Video chip in the Spectravideo also get very hot too. I wonder if there's away to increase the efficiency somehow... My new floppy drive consumes a max of 960ma, apparently, which is not the best, but I'm just so happy to have a working DSDD floppy drive in the 738.
£49.95 is a lot for a PSU, though it's not 100% awful of a price. Would you be offering a UK plug version / figure of 8 or kettle lead input? I'm really intrigued about what your PSU is like, anyway :)

I'm really happy that this thread is getting some attention. The Spectravideo 738 is such a fantastic MSX and really awesome for modding! :RNFF:

By mxmy

Resident (39)

mxmy's picture

20-07-2018, 05:11

I'm also really curious about the missing transformer(?) at L1 on the power board. Was this something that was only used on certain regional models, or was it something that SVI were too cheap to include? On my model, it's simply a couple of wires to bridge the holes...

By CopperPod

Supporter (5)

CopperPod's picture

20-07-2018, 18:32

The PSU is sadly not based off of the original. In fact, I've never seen the original, as my X'press came without a PSU, thus my "hunt" for a PSU ; ) I can't even find a photo of it on the net oO
Anyway, the original is only 2A, which will cause it to get hot when running at limit, like when adding the new disk drive or other extras. A 2.5A or better 3A will suit you, as the computer only draws the amps it needs. I have a ready to use PSU (Bought in Australia, which ended up costing me £60 in price, shipping and import taxes; why I'm trying to produce a cheaper option with choice of either 2.5A or 3.125A and either EU or UK plug (yes to your question)).
Anyway, that PSU is 16v AC at 3A, and I can have the SVI-738 on for hours, and there's hardly any temperature change (cool to the touch). And, of course, the newer transformer types is of a much better quality than the ones 30 years ago.

The ICs that tend to get hot should be heatsinked, maybe some of these low profile heatsinks will fit:
Either side by side:
https://www.ebay.co.uk/itm/263381923648/
https://www.ebay.co.uk/itm/262736530858/
Or cut to fit:
https://www.ebay.co.uk/itm/192464298749/
https://www.ebay.co.uk/itm/282894299435/

By Pablibiris

Paragon (1657)

Pablibiris's picture

21-07-2018, 00:31

Too expensive for a power supply Sad

By CopperPod

Supporter (5)

CopperPod's picture

21-07-2018, 01:19

@Pablibiris
Yeah, sorry, I know it's expensive, that's also what I said from the start Wink But try to find one that will fit the X'press, at all. 0.5A and 1A PSUs are very easy to get very cheaply, but if you want to get up to 3A, the price skyrockets.

@mxmy
I'll be selling one of the AU PSUs (I bought two). But at £59.95 just to break even, I have another offer for you. I'll sell you the first CopperPod PSU (16VAC, 3.125A) for £39.95 w/UK plug. You don't have to decide now. Just to let you know Big smile
I might have found a cheaper supplier from Germany, and hopefully that'll be nearer the price.

Cases that will be available:

By mxmy

Resident (39)

mxmy's picture

26-07-2018, 08:17

The price coming down and getting the first one sounds good Big smile Please keep us informed about how it goes with the german supplier! Also, the first PSU case easily looks the nicest IMHO. The 3rd looks like likely to have problems via people spilling drinks on it (and smell from dust getting inside) and the second one is white, which gets dirty rather quickly...

Totally okay with adding 3M anti-slip feet on the bottom (if at least to keep it from dragging on the floor), but if it comes with them, that'd be even better.

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