My NEC PC-8401s' LCD Module Faces Capacitor Issues
I'd noticed, well couldn't help noticing really that the PC-8401s' LCD screen would flicker, and every now again turn off unexpectedly after extended use. Over the last week the occurrences became more frequent. Interestingly or comfortingly the screen flickering has no effect on the Main Computer, everything stays resident, you can even continue typing while the screen is off. So what ever the problem? It is appeared localised to the LCD screen. Time to pry open the computer and see what's happening.
A quick look over the main board revealed nothing of immediate concern, though at some point I'll want to replace the NICAD backup battery and the 30 year old capacitors, thankfully though none of these components have been leaking. Semi confident the main board is okay it was time to crack open the LCD bezel, not the most convenient thing to do.
NEC PC-8401 Main Board
Unlike the main case the bezel is mostly held together with molded plastic clips, taking it apart took some considerable carefully spent time. Once off however it was immediately clear where the problem (hopefully the only problem) lay.
NEC PC-8401s' LCD Panel
We've got 2 exploded leaky electrolytic capacitors that need to be replacing, and while we're at it the other 10 should be swapped out for good measure. I guess considering the age of the computer this is not unexpected, all this is really part of the excitement of playing around with old hardware.
Some Picturesque Leaky Electrolytic Capacitors
Well then, before continuing any further it's of the the electronics supplier to procure some of these tiny caps, of which I have exactly none of in my parts draw.
As a quick aside the panel was manufactured by Epson.
A while ago now I fitted the very cool and reasonably priced ZXCCB composite video mod into a ZX81, yielding a much improved video experience, yet this is only half the story in the quest for retro ZX81 video perfection.
There is many a web page or YouTube video devoted to video outputs on retro computers and gaming consoles. Mostly these deal with the somewhat later computing or console incarnations such as the Sega Mega Drive, Nintendo NES or Commodore 64s. There are some excellent write ups on the subject, and you can't go past RetroRGB.com for some solid information well beyond the scope of this article. The ZX81s video demands though are rather less unassuming than most, requiring only the display of a (hopefully) clear black and white image.
What kind of perfection are we after? I say video perfection, this is a perhaps a little misleading, as what I'm really after is a video experience, an experience that captures the heart of ZX81 usage. This is of course a rather esoteric requirement, if perhaps partially at the heart of using the real deal instead of a emulator to start with.
Below are some of the variations on a theme I've tried, this is not an extensive list of every possible configuration available. So this is not a guide, more of a primer before launching your own quest down the rabbit hole of ZX81 monitor selection.
To CRT or LCD?
Back in the 80s the best monitor for a stock ZX81 was a black and white television. The perfect monitor for a ZX81 with a composite mod in 2017 is probably a black and white monitor with composite inputs. Simply put, the ZX81 does not output a chomiance (colour) signal, only a luminance (black and white) signal, any colour induced into the picture is by pure accident. There are not a great deal of black and white monitors available these days, so what easily available monitor options are available in 2017 and beyond?
There are a whole host of options available these days, from old CRTs to video converter boxes and new LCD televisions. The choice is only limited user preferences and in some cases by the constraints of the ZX81s video signal and it's interaction with modern devices. My personal preference varies, on the whole though I'm rather taken by Sony Broadcast monitors as these induce that all important retro feeling.
Option 1: An LCD TV
ZX81 with LCD television as monitor.
Most (I'm not going to say all as there are weird regional variances) LCD TVs still have Composite video ports. The ZXCCB video mod, the ZXVid and others, are designed to take full advantage of the Composite inputs, outputting a stable and clear image to modern LCD TVs. Frankly the clarity of the ZX81s output on a decent TV is astounding, even on low rent LCD TVs the image quality is far sharper anything you've ever experienced on an unmodified ZX81.
At this point, If you're happy with LCD displays you can stop right here, your never going to get a clearer display out of a ZX81, still there are minor issues with the display, and your personal preferences play a part in the ultimate monitor selection.
It's difficult to find an LCD TV with a 4:3 aspect ratio, meaning that text and therefor the underlying pixels are always going to look elongated. This may or many not be a worry, certainly the enhanced video quality more than makes up for the distortion. Then again anyone after retro video purity may well take some offence at lack of near squareness in the aspect ratio. Of course an LCD monitor may already fall into the abyss of impure horrors for those with high retro tastes.
I have found that some LCD televisions play up a little when loading tape, loading from the ZXpand or going into fast mode. Anytime the Sync signal is dropped by the ZX81 an LCD televisions may revert to a blue or black screen momentarily, where most CRT monitors will retain the greyish background or display the loading bars normally associated with a ZX81.
Option 2: The CRT Colour TV
Late model TV with the ZX81 using RF out.
The best part about these is that they are (at the time of writing) cheap, though a slowly disappearing resource. I was lucky enough to find a late model 32cm (14inch) xxxx on the side of the road a couple of months ago, I was initially quite happy about that. I say initially as while the general image clarity falls in the okay-ish zone, the refresh rate on the monitor is headache inducing.
Refresh rate is probably misleading here as technically speaking all PAL TVs and monitors are refreshed at 50htz. This may really be a phosphor persistence rating problem. The rating of particular coating thi inside particular model seems to be just high enough to mostly maintain an image between refresh cycles. Doubtlessly this is not the only reason for this units headache producing flaws.
On the positive side, the TV has AV inputs for a very clear image, though more interestingly it also has no issues in picking up a ZX81s RF signal, producing one of the clearest images I think I've ever seen RF wise. So if you're not keen on modifying a ZX81 for composite out a late model CRT TV might be the best video output option.
Regardless of the positives, using a standard TV as a computer monitor in 2017 is just plain awful, even if you're after that retro CRT experience. Sitting up close to a standard flickering television is underwhelming, did we really do this 30 years ago?
Option 3: A Professional / Broadcast CRT Video Monitors
Sony 9inch PVMs
Broadcast and Professional monitors are without doubt one of the better go ways to go if you're after an old school CRT feel without compromising high legibility. These monitors are designed for people who's job it is to make, view and breath Television 24 x 7, so the clarity gained, particularly from the high end editions of these monitors is breath taking for CRT.
Presently being discarded by the TV industry, PVMs and BVMs are highly coveted by many a serious retro gamer. Sought after PVMs are typically 20 inches plus, with extensive features including Composite, S-Video, RGB and YCbCr inputs. All this providing an expansive, high quality retro gaming experience suitable for most retro consoles. Of course a ZX81 in no way needs all the higher end features, we're just after a clear picture.
A ZX81 isn't going to be used from the couch or armchair, most likely it'll be desk based, so clarity is probably the foremost factor in choosing the monitor. Sizes over 14 inches aren't going to add much to experience, and RGB and YCbCr are nice to haves but not important unless using you're also planning on using the monitor with more advanced micros.
Nicely I have 2 Sony PVM monitors, a PVM-9040ME a PAL only monitor that has S-Video and Composite ports and a PVM-9042QM monitor with a full spectrum of video inputs available. Both monitors have screen sizes of 9inchs, a small size by today's standards but not so tiny by the standards of the day. These monitors provide a beautiful viewing experience.
Option 4: Video Upscalers and Converter Boxes
Given the vast supply of LCD VGA and HDMI monitors in circulation, video converter boxes seem like an obvious usage case. But, and this is a big but, not all converters are created equal. Finding a converter box that worked with my ZX81 has proven problematic at best, though individual mileage may vary considerably.
The ZX81s video output, even with a ZXCCB installed is dependent on the version of ULA inside. While the signal can be corrected for missing back porch, the underlay signal generation may not be exactly to PAL standards. I'm not am expert on the subject, but given the lack lustre results using various converter boxes which for all intensive purposes work fine other conversion duties I'd guess this is the cause of the problems I've encountered.
The best converter box I've found is a rather ancient one, an Aver Media TV Box 5. It's unfortunate that the maximum resolution this will pump out is 1024x800, somewhat below the capabilities current generation LCD VGA monitors. For this the TV Box suffers a little, as monitors perform best at their own native resolutions and the resulting image is just a touch blurry. Of course that does feel a little more retro.
I've put up a little video that highlights the problems or successes of various converter boxes at my disposal. The best I can say is buy one at your own risk, and at the end of the day a cheap LCD television seems by far a better option.
What is Monitor Perfection?
The choice of monitor really comes down to personal preferences. If after a clean and sharp emulator like quality, I've found even the least expensive LCD television is capable of delivering a stunning image (for a ZX81). For a that fuzzy feel good retro experience my preference falls defiantly in favour of PVMs and other broadcast monitors. Just remember that most of these video options are only available once the ZX81 is fitted with a composite modification such as the ZXCCB or ZXVid, both of which are regularly obtainable from the Sell My Retro web site.
My Sourced ZX81 was Modified for the American Market
Having played around with emulating the ZX81 as part of building a Raspberry PI / Arduino platform in the AZ15, I thought it might be fun to revisit the real device.
To start I'd be needing a ZX81, a process that proved trickier than anticipated. There should be no shortage of ZX81s in Australia, yet they seem sparse enough to command high-ish prices, high enough to send me searching further afield. European and UK prices again seemed rather expensive, particularly if including postage. So to the USA then, a Timex 1000 would be just as acceptable, in the end I found a reasonably priced American fitted out ZX81, obviously sent to the new world before the official deal between Timex and Sinclair.
So what exactly can be done to update and bring a ZX81 into the now? Well, there is a great deal of information out there concerning the upgrading, modifying and repairing of ZX81s. Should you decide to do everything from scratch the information and resources are available. However the really good news is that many of the parts required for a refurbishment and upgrade can be bought right off the shelf.
New or Replacement Power Supply
Before even turning on my ZX81 for the first time (in my possession at least) I needed a power supply, my unit came sans power brick. While I had no option but to source a new supply, it's recommended that even if you still have an original Sinclair unregulated power brick that you should still replace it with a switch mode equivalent.
An original Sinclair unit is rated at 9V, however as the supply is unregulated that can get as high as 12V, this leaves the ZX81s internal regulator doing all the heavy lifting. Governing the required 5v (down from 12V) leads to an excessive amount of heat being generated inside the case.
You can use a regulated power supply of anywhere between 7.5V and 9V with a minimum 1000mA (1 Amp ) current draw. The easiest or most available substitution seems to be regulated 9V supply. The power supply should also have 3.5mm phono plug jack plug at the business end. Power input of +7.5V to +9V should be at the tip of the plug, with the lower / outer ring being ground.
I picked up an appropriate Switchmode Plugpack 9VDC 1.66A from Jaycar (Australian Electronics Chain), the unit provided a variety of jacks that can be substituted as or if required. Similar Plugpacks should be available just about everywhere. Ebay often seems to have packs marketed as being specifically for the ZX81.
Optionally a power switching cable can be added between the supply and the ZX81. This will save some wear and tear on the ZX81s power socket These can be made easily enough, or purchased from specialist suppliers such as the Retro Sparse Shop, that's if you don't want the hassle of tracking down appropriate parts yourself and in all actuality might prove more cost effective.
Composite Video Output
The second thing in need of attention is the video signal. as the combination of modern (not the best quality admittedly) LED TV and RF signal emitting from the ZX81 is terrible to say the least.
There are various video mod available that will provide composite video out, ranging from ones that you can build yourself to others ready to fit into the case with minimal fuss. I've gone with an off the shelf fix in the form of the ZX8-CCB, a video mod created by the venerable Pokemon. The ZX8-CCB is available from The Sell My Retro website. Before going into the fitting of the ZX8-CCB, lets quickly look at other composite video mods.
If you choose to build your own then it would be hard to do better than the mod by Joulesper Coulomb detailed in the YouTube video, 'ZX81 Video Conditioning'. A lot of effort has gone into the mod, and spectacular results have been achieved, which can clearly be seen in the video. Minimal parts are required to undertake the modification, it is easily assembled on strip board and once built, the entire project can be housed in the existing ZX81s modulator case.
There are slightly easier mods to build yourself, most of these use a single transistor and a some resistors, such as the simple mod by the ZX-TEAM. You can see the results of that video modification on Terry Stewart's (retro computer collector extraordinaire) web page. However, these simple mods may not work so well with earlier issues of the ZX81 due to a missing back porch signal, and possibly leaving the resulting picture a little on the dark side.
For off the shelf options, there is the Atari (yes you read that correctly) composite video mod for the ZX81, sold by The Future was 8 bit. Dave Curran on his Tynemouth Software Blog, details the fitting of this interface to great effect. Lastly (of course there are bound to be more), there is the Sinclair ZX81 ZXVid - Composite Video/ULA Fix, available from Sell My Retro. You can see the results of this mod on the YouTube video ZX81 - ZXVid board, Composite mod.
Fitting the ZX8-CCB
The process of fitting the ZX8-CCB is very well documented in the instruction sheet supplied with the kit. There is no assembly of the kit required, and it's down to a little soldering to the ZX81.
To start, it's simply a matter of attaching the input wires to the back of the ZX81 circuit board: red wire +5V to ULA pin 40, the black wire 0V to ULA pin 34 and the yellow wire to video In at ULA pin 16.
For the output wires you have a choice to make, either integrating a small video jack (3.5mm) between the two cover parts (as suggested in the instructions sheet), or re-purpose the modulator casing. The second option is what I decided to go with.
In order to fit the ZX8-CCB into the modulator case, the case needs to be removed from the ZX81 circuit board. There are 2 or 3 wires going into the side of modulator, these can be trimmed of at the base, or de-soldered. Also there are two large pins directly underneath the modulator, these hold the modulator unit in place. These also need to be de-soldered to remove the modulator from the ZX81s circuit board.
Once the modulator casing is free from the ZX81 you can then set about removing the existing contents (though a combination of cutting and de-soldering). What's inside the box will vary depending on the modulator, on PAL models there is a cross bar and the main circuit board to remove, as I have a USA model there was no crossbar.
ZX81-CCB Input Wires Soldered at the Back to the ZX81 Circuit Board
After the modulator has been gutted it can then be re-attached to the main circuit board, with the ZX8-CCB placed inside the casing affixed with a square of double sided tape. The remaining wires are then attached: brown wire for video out to the center of the phono socket, and the the black wire 0V to to the side of the modulator casing.
ZX81-CCB housed insdie the Modulator Case. (Wires latter moved to run through vaccant holes in the casing)
In the initial fitting I had the three wires which are soldered to the ZX81s circuit board running over the side of the modulator casing. With the modulator lid placed back over the top, this was perfectly serviceable but looked a little untidy. I latter decided to move these wires and have them running through the now vacant holes (of which there are three) on the side of the modulator.
Composite Results
So what of the results? In a word 'amazing'. It is unfortunate that I don't have a CRT TV laying around to give the proper picture, though even upscaled through a composite to VGA converter box the clarity is almost as clear as on many an emulators, it's certainly the best video I've even seen emanating from a ZX81.
After Composite Video Mod (with a little HRG graphic teaser)
Of course I'm not the only one to have retrofitted a ZX8-CCB to a ZX81, these things sell like hotcakes. And as is the way with these thing, half way through typing up this post I found another blog post detailing a similar install of a ZX8-CCB. I'd suggest checking out Kevin Phillip's entry 'Rejuvenating My Geriatric Childhood Friend' for extra information. The better you're informed before making any medications there better.
Next Time
There are a couple more modifications I'm wanting to make, along with a couple of interface addons to try out. (Hint one of the is in the final picture). I'll get around to detailing those and more soon.
