Sony Hit Bit MSX HB-75B restoration repair attempt

[dicky96]

Hi guys I've not been on the forum for a while as I have been busy with a new business venture


Anyway, last weekend I was at the local flea market and found this Sony MSX Hit Bit computer

I decided to buy it just to see if I can get it working, and because they are quite rare. From the outside it looks pretty much OK but what I found inside was a bit of a surprise!!

It may even work, I don't know but I am not inclined to power it up in it's current condition!

Fortunately I don't think there is actually anything alive in there, but where to start? Take it all apart and scrub it in a bucket?


here are some nice pics!

Rich

[SMDFlea]

Re: Sony Hit Bit MSX HB-75B restoration repair attempt

Its seen better days,needs a good cleanup first to check for corrosion. Theres a service manual/schematic from archive.org

pdf version: https://cdn.badcaps-static.com/pdfs/...21d2ee6276.pdf

https://archive.org/details/sonyhb5575sm

[dicky96]

Re: Sony Hit Bit MSX HB-75B restoration repair attempt

Cheers for the schematics

I think in the instance of this computer, the FLEA market was a good description of where it came from lol Well more Cucarachas than fleas but I woudln't be suprised if there were some in there

OK it is all stripped down and it's going in the bucket with the garden hose!

[dicky96]

Re: Sony Hit Bit MSX HB-75B restoration repair attempt

I got this all cleaned up, but I have a couple of problems with it. The big problem is that the linear power transformer seems to be faulty - when powered up with a light bulb mains limiter, it draws quite a lot of power and there is hardly any output on the 12V winding and no output on the 5V winding

I used my bench PSU (dual output) to supply power to the main smoothing caps after the 5V and 12V rectifiers. I can see that the Hit Bits voltage regulators are working correctly as they stabilise at 12V and 5V once I increase my bench PSU outputs over 14V and 6.5V respectively.

The Computer seems to power up but I have only line sync and frame sync on the composite video output. I had a quick poke around the pins of the ROM chips and it looks like all the address and data lines are running.

But without a working mains transformer I don't see how I could get this working so I don't know if it is worth spending time on it

Rich

[momaka]

Re: Sony Hit Bit MSX HB-75B restoration repair attempt

OK it is all stripped down and it's going in the bucket with the garden hose!

Yup, that's the standard procedure for almost anything dumpster-picked or 2nd hand device I get here. Warm water + soap detergent + let it dry under the sun for a few days usually gives pretty good results. Though if it has live roaches, your best bet is to leave it outside for a while sprayed with something to drive/kill the bugs... or if it's very cold (well below freezing) or very hot (allow the device to heat to 50+C under the sun), that's the most natural way to do it (and how I usually do it.)

Regarding the transformer, try removing it and powering it up by itself only (also make sure it's fully dry from water if you had it washed too.) Then see if it still draws a lot of current/power by itself. I don't imagine it should draw more than a few Watts connected at the wall (though beware that some cheaper power meters can get confused between the VA and Watts, and show much higher readings, so make sure your meter can read both W and VA, and preferably PF too, since it's normal for linear traffos like this to have high-VA draw when unloaded, but low Watts.)

[RJARRRPCGP]

Re: Sony Hit Bit MSX HB-75B restoration repair attempt

Hi guys I've not been on the forum for a while as I have been busy with a new business venture


Anyway, last weekend I was at the local flea market and found this Sony MSX Hit Bit computer

I decided to buy it just to see if I can get it working, and because they are quite rare. From the outside it looks pretty much OK but what I found inside was a bit of a surprise!!

It may even work, I don't know but I am not inclined to power it up in it's current condition!

Fortunately I don't think there is actually anything alive in there, but where to start? Take it all apart and scrub it in a bucket?


here are some nice pics!

Rich

Looks like pill bugs and a cricket. Looks very much like what the region I'm in gets regularly, LOL!