Fixing and upgrading an Enterprise 64

[PhilC]

As you may have seen, this arrived a couple of days ago.

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So today I've dug out a power supply for it. It's 9V centre negative btw, similar to the spectrum of the same era iIIRC.

So I couldn't be bothered to dig out my old CRT TV to get it tested, so I did a composite mod that can be found on Retro Fixers website. I'll post it here as well in case anyone would like it.

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So you can do a quick mod to the UHF modulator and your good to go but instead I decided to remove it and fit the parts directly as seen below.

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I used a BNC connector for the video out (partly cos it was all I had) so that I can use the same cable as I use on my Beeb.

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I've got to fix the broken heat sink cover at some point (if I can be bothered) as you can see above.

Next steps are creating an extension for the keyboard membrane as it's a pain to lug in. Someone has shortened it at some point. Then recap the electrolytic caps as these are a known failure point in these where Philips caps have been fitted.

Then it's time for a ram and rom upgrade.

More to follow

[PhilC]

I ordered a new keyboard membrane for the enterprise which arrived today instead of lengthening The original one. Also some new axial capacitors arrived to replace the ones on the motherboard. I'll also install the ram expansion header whilst I've got the motherboard out of the machine and do the rom replacement.

Then it's just a case of obtaining the PCB for the ram expansion and then building it.

Once it's done I may even bring it to Cyber Legends 5.

[alexh]

Enjoyable read. There's been a few affordable untested Enterprise 64s on various auction platforms recently. I've been very reluctant to hit buy but if you get on ok I'll have a punt

I see you can get RGBTOHDMI pickup boards for the Enterprise 64. Cheaper than a SCART cable

[PhilC]

Enjoyable read. There's been a few affordable untested Enterprise 64s on various auction platforms recently. I've been very reluctant to hit buy but if you get on ok I'll have a punt

I'm not sure I would get one that's a non runner as such as there are two custom chips on board.

One with garbled text etc is worth a punt as that's usually a couple of transistors and a recap needed.

[PhilC]

Did a bit more work on the Enterprise today.

Replaced all electrolytic capacitors.

Removed composite mod and replaced with simple wire link as it was causing my upscaler to flicker all the time. Quality isn't the best BUT I'm going to make an RGB to scart cable once the 14 pin edge connector has arrived from China.

Upgraded the rom yo Exos V2.4 as this includes a basic interpreter and is the latest available.

Fitted the new keyboard membrane.

And gave it a good test.

I'll be ordering an SD card interface once I can find one and ordering the PCBs for the ram upgrade soon as well.

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[PhilC]

I made up a Scart cable for the enterprise today and noticed some odd behaviour which I had previously attributed to a problem with the composite video.

Doing a simple basic program to put assending numbers on the screen. It would pause and the screen glitch.

CSync was actually pretty stable, so it wasn't that.

Messing around with pots on the motherboard there's a small variable cap C34, that when I adjust it, it can cause the glitching. It's right next to a 4mhz oscillator, so I suspect the clock circuit is a bit dodgy, so next job is to learn the circuit and then diagnose the issue.

Other than that. It seems to work just fine.

[rubber_jonnie]

If you have issues with clocks you could try my clock replacement here: ReClock

You can replace up to 3 clocks with it, but you just need to identify the correct location to feed in the clock as it isn't a crystal replacement.

[PhilC]

The floppy and ram PCBs are now on their way from China, so I've got the Enterprise on the desk once again, to try and stop the stuttering issue.

Using a simple a=a+1 print a test I was previously able to cause the computer to pause / stutter for a fraction of a second every so often.

So far today I've fitted a proper heatsink onto the graphics chip, uprated to a 5 amp power supply in case that was asking to the issue and have once again been playing with the C34 variable cap.

So after a few false starts where I thought I'd fixed it, only for it to go wrong when I turned my back on it, I now "think" I've fixed it.

The heatsink on the graphics chip was originally a copper plate that got pretty hot. The new one still gets warm, maybe 40 - 50 degrees, so it definitely needs one now, likely due to component age etc.

So I'm going to leave it running for an hour or so and see what happens. I've got both my fingers and toes crossed this time

[PhilC]

Well.... That didn't work.

Something getting hot is causing the horizontal sync on the video to fail and the stuttering to resume.

I'll have to get some freeze spray to try and work out what but hopefully my cheap thermal camera will also point me in the right direction.

[PhilC]

So just having a bit more spare time this evening, so I've got the scope out and the Enterprise running showing the flashing enterprise logo, which does work well for diagnosing this stuttering and sync fault.

So I've tweaked C43 for the maximum clock VPP which is around 2.9V and I was still getting the sync issue. I've reflowed the crystal and the resistors in the circuit near it and it and for now at least the sync issue is behaving. So now I just need to see what's causing the stuttering.

The enterprise does use an LM1889N like the spectrum, so I do at least have spares for that and possibly a spare crystal too, its 4.433519mhz for those that are interested. In fact I may swap it anyway to rule it out.