Issue 6a ZX Spectrum 48K Repair - From Knackered to New

[@cressytisswuff]

How dare you, the amiga games weren't naff! Love the text adventure summary.

[@EmmittBrownBTTF1]

One thing to do is replace the 7505 voltage regulator with a switchmode regulator, they run cooler, which extends the life of other components.

[@andygozzo72]

wont make much difference..

[@EmmittBrownBTTF1]

@@andygozzo72 You have no idea how much energy the 7505 dissipates, it's dropping 9V to 5V, the heatsink gets painful to touch. Without a heatsink the 7505 kills itself in a few minutes. A switchmode regulator(the can be a drop in replacement) can safely run without a heatsink, showing how much cooler it runs. The ULAs are no longer manufactured, and Sinclair over exploited them in the design, so they run hot too. The two together are a recipe for failure. the other thing to do is of course heat-sink the ULA. The heat also contributes to drying out electrolytic capacitors. The 128k Spectrum had an external heatsink and was dubbed a "toast-rack". Sinclair designed their machines to be cheap, and pushed the technical limitations of the components.

[@andygozzo72]

@@EmmittBrownBTTF1 yes, without it, it could fry(they're supposed to shut down with excess temperature, though) thats why they have a heatsink ,, loads of other devices use those linear 3 terminal regulators, some running hotter than in a spectrum, with no real issues ,

[@markbell5590]

Thanks for the video. I learnt a few things from watching. I am from Warrington and remember Pyramid Micros fondly. I bought a few Spectrum games from there in the years it was open.

[@muskett00]

Great video, love the ending

[@andygozzo72]

i strongly advise using a cap for composite out, and possibly reducing the emitter resistor of the modulator drive transistor as will improve the negative going edges of the signal ..

[@bbjunkie]

You'll find it took a lot of force for the VLA as it has round pins, the original ULA has a flat single wipe style. To do it right you need to replace the socket from single wipe to turned pin type.

[@redhawk668]

Nice video, in most cases TR4 and TR5 are indeed knackered. In some cases the coil could be knackered too.

[@andygozzo72]

definitely, a shorted tr4 can destroy the coil, it melts the wires enamel coating causing shorted turns, replacing tr4 without replacing a damaged coil will soon destroy the new tr4! guess how i found out!!!!

[@InfiniteLoop]

Nice, I had an 81 as a kid, but it was lost several years ago, always wanted a spectrum but they’re not available in the states.

[@HappyLittleDiodes]

I've shipped a few over the pond ;)

[@andygozzo72]

there was the USAs own variant of the spectrum TS2068, unfortunately not fully compatible unless you fit a spectrum rom in place of the original

[@RuiMartins]

Long time after, but the video output in the end is a bit weird. Most noticeable in characters "t", "o", "m" and "w". Could it be due to the vLA82 or the video chip itself?

[@HappyLittleDiodes]

Good eyesight, that's an interesting observation. If I ever get my hands on another VLA82 I will compare

[@tenminutetokyo2643]

Jam in a TSR-1 2450 and you can dump the heat sink too. And it runs cool as a cucumber. $5 bucks on Mouser.

[@HappyLittleDiodes]

Good tip. I've got a drawer full of them. I'm often torn though because you lose the authentic heft and warmth that the 7805 and the heatsink generate

[@andygozzo72]

minimum dc in is between 7.5 and 8v ...lower than 9v reduces heat in the regulator but stresses the dc-dc converter more as it has to work harder to get the +12v up ...

[@gingerhippygaming7962]

Great video mate I do love the spectrum

[@HappyLittleDiodes]

Thanks buddy

[@mikekelly9129]

I am after fitting a reset button to my issue 6a, could you please point me as to the exact location of where to put the wires from the switch, many thanks 👍

[@HappyLittleDiodes]

Hi Mike. You can solder the two wires to either end of C27. See the bottom left of this schematic. RESET is active low, so you need to short it to ground to cause a reset. spectrumforeveryone.com/wp-content/uploads/2017/08/ZXSpectrumIssue6a-Schematics.gif You can see it on a 4S board here kzbin.info/www/bejne/hIC4l6uZpbVmjsU

[@mikekelly9129]

@@HappyLittleDiodes Thank you so much for getting back to me and taking the time to show and explain how to do it. Definitely made a subscriber here 👍

[@skjerk]

Best adventure game ever :-D

[@HappyLittleDiodes]

My boss still asks me why he was in a pile of leaves!

[@ElectronGordo]

Hi, could you tell me what was with the wrong lines on the screen after ULA and Memory Replacement? I could tell some horizontal random lines on the screen. Thanks

[@HappyLittleDiodes]

I think you are just seeing an interference pattern between the resolution of my camera and the screen

[@ElectronGordo]

@@HappyLittleDiodes No I am not. Minute 6:00 just a second before also later... about middle... centre of screen... and later appear some more. I have also this board and I changed some toasted memories and the ULA now it works but with those... glitches. Trying to figure this out.

[@HappyLittleDiodes]

@@ElectronGordo Yes, you can also see that the screen jumps right a couple of columns. Later in the video I swap the ULA and it's OK afterwards.

[@HappyLittleDiodes]

Do you have another ULA to try?

[@ElectronGordo]

@@HappyLittleDiodes No I have not, but this one works fine, cause it took it off another Spectrum and has not this problem. But with this Issue 6A appears. I will watch your video again, I thought they were there even after ULA replacement.

[@izoroza]

great video, learned a lot about the spectrum's inner life! I also have a issue 6A 48K motherboard that has gone dark - no video, no clicking key sound. Did all the same testing as you do, I initially have all voltages in the 7805 regulator and lower/upper banks as per your video. but shortly after the voltages start to come down... I measure 4V at the regulator "out" and for example teh 12V at the RAM lower bank shows 9 to 10V... Do you think I should just change the 7805 regulator? Or transistors as well? Thanks!

[@HappyLittleDiodes]

Was the board working previously? If so, I would recommend a new 7805, new TR4 and TR5, and then find a video by Joulespercoulomb "ZX Spectrum Initial tests" and follow along. If you get to the end without any funny business then power it up and see what you get on the screen.

[@izoroza]

@@HappyLittleDiodes Perfect. will do so. actually , since I am at it, think i can replace the 7805 with a newer / more efficient regulator to have less heat dissipation, would you agree? thanks again.

[@HappyLittleDiodes]

Yes you can use a Traco TSR 1-2450. I think Murata also make one which is slightly cheaper

[@MagicMikeSmithMusic]

I like the adventure game!

[@JohnSmith-bh4zx]

A noob question, I can't see where you get the address 55000 from, for the Peek & Poke commands @ 7.41 ?

[@HappyLittleDiodes]

The address doesn't matter, as long as it resides in upper RAM, which is all addresses between 32K and 64K. I think I only chose 55000 because a website describing the trick used that address.

[@stickybandit2346]

So are you saying that your new vla82 was bad?

[@HappyLittleDiodes]

In hindsight it's probably more likely that it just needed reseating, as it worked in the other machine I seem to remember

[@liamwhitcher9059]

yes, glad I stayed for the end adventure game. Reminded me off similar where if you ran out of patience and typed in a swear word the game would re-set!

[@mddaly6082]

I spent hours in Pyramid Micros in Warrington.

[@SyldabiaHacks]

Really if you tests 40 years old capacitors in capacitance and ESR, you can see all are correct. The better things have a ZX Spectrum I think was the capacitors. It's not necessary remplace in general any one.

[@peter486]

:))))

[@helijim]

Great video but I think you were mad to power the thing up without doing the capacitor replacement first. Powering up with old or bad caps could cause things to fry so that should be your very first job.

[@HappyLittleDiodes]

I've yet to come across a speccy with a bad cap that has caused any trouble, you're right though, it can happen. I would certainly do that if any of the caps were clearly failing from a visual inspection.