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ZX Spectrum 48K Repair. I could really use some help from the other side of the pond repairing this...

I'm not sure about the varnished ones... You would have to ask him. I doubt he is winding conductive wire around it, but in this modern world, all kinds of weird things are possible. Maybe there's a difference between enameled and varnished, or maybe he means the whole thing is varnish dipped after construction? I don't really know. I've never bought one. Let us know if you find out though.
 
According to the schematic there are only four pins actually used.

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The 'black dots' indicate the 'start' of each winding.

The PCB (and the former upon which the coils are wound) are probably fairly generic. If you look closely at the pinout of the transformer on the Spectrum you may see only four pins wired - or you may see more (but some pins joined to others) to make the layout fairly generic.

Is it cheaper to wear some headphones and listen to your favourite music whilst playing with the machine?!

Dave
 
Yes it is cheaper Dave. But in the end this is a gift to my wife. And when I work on a machine for someone else it better be near perfect when finished. Just the way I am. If I am going to cut corners I will do that for myself but not if its for someone else.
 
I received a reply back from the seller"
Yes,
This will work on your Spectrum. The middle pins are just key pins and one of these is adequate (which is what was decided with the later coils which were made).
My varnished coils are silent and will stop any noise.
Regards,
Paul"
 
So I bit the bullet and purchased the Varnished coil. One more item to wait for with the keyboard membrane. That hasnt shipped out yet though. Hopefully soon as its a month lead time to get here.

Before I purchase an SD option I would like to try loading programs and games from my phone, maybe with Tap Player. I take it I will only need a basic 3.5 MM audio cable from my phone to the Mic input?
 
Yes, any audio signal should be OK, but I don't know what voltages your phone ear plug puts out - so it might not be strong enough. Playing with the volume is something we all used to do to try and get it right.

If it doesn't work from your phone, it will probably work OK from your PC, and yes, a MP3 of a game should be sufficient. Even if it doesn't load, as long as the color bars are present it should be OK. In fact, once it starts seeing some noise, the screen border should flick back and forth between it's two main colors and will then start with the bars if it gets the right timing on the lead-in sync. Even music should be OK as just static at the start of the tape caused it to flick back and forth at times.

Having a new coil will ensure that any damage that can't be seen is eliminated. Don't forget to remove all the 4116's when you test the new coil :) ( Maybe I am being overly cautious there ).

BTW, when your new membrane comes, some keyboard templates only had sticky tape, but I've seen some which had pieces of metal glued that went through the top plastic housing and kept it firmly down. Also, if you bend it when you take it off, it never goes back straight. A little curvature at the ends upwards will help keep a touch of tension when you stick it back down with double-sided tape, but if it bends upwards in the middle, it's a mess and will never sit flat again. Something to keep in mind when you remove the plate over the rubber keys, if you haven't ordered a new one.

David.
 
cj7hawk said:
Having a new coil will ensure that any damage that can't be seen is eliminated. Don't forget to remove all the 4116's when you test the new coil :) ( Maybe I am being overly cautious there ).
Click to expand...
You mean remove all the RAM and then power up and listen for "noise"?

The metal keyboard bezel already fell off. IT was held on with two strips of double sided tape that mummified. I will clean off the residue and get new double sided tape.
 
No, just when you replace the coil :) Just in case anything goes wrong with the -5 and 12v rails, it's worth checking them before you put the ram back in. ( Unless you happen to have a lot of spare 4116's ).

Also, don't forget to put a piece of sticky-back foam on the video modulator. If the new keyboard membrane sits on it ( it will ) and rubs on it during operation ( it will ) then it will wear a hole in the membrane that may not be easily visible, bit will short out the keyboard lines, and also likely crash the machine. This is a common fault in spectrums, and is why many machines had that foam in there from factory.

David.
 
I have a handful but they are not easy to come by so I will do that for sure.

Thanks for the heads up on the foam for the modulator. But does that apply since I removed the orignal modulator for the composite video board?
 
It was the grounded metal case and vibration that was the problem. It probably won't be such an issue then with the circuit board. I never thought of that.
 
cj7hawk said:
Congratulations ! Mostly they aren't anywhere near this difficult to fix. Any remaining faults should be easy to fix now :)

The speaker should not squeal, as there's not supposed to be an amplifier in there, so unless the ULA is sending it some weird sound, that's a curious issue. Definitely one for the oscilloscope - Pin28 on the ULA is the sound output I think. It should be stable and not oscillating or changing level. The sound circuit is very simple.

I get my keyboard membranes from Retro Radionics. - https://retroradionics.co.uk/

They price in US dollars, and ship from China. I find their service and quality to be very good, and the price is good. You can also get a new faceplate and other parts from them if needed... Maybe even customise up the Speccy with your wife's favorite color.

You could hardwire in a few keys to allow you to type "Border 1" or something like that to make a color come up, that would be 3 keys in a quickly assembled matrix ( B for Border, Then any number from 1 to 6 then Enter ) which would take just a few minutes, or you could work out which keyboard connectors to short and just short them to type, since it's a very short sequence... I'd probably just short the keyboard connectors in the right order at least once to check if it was an issue I needed to solve.

Or if you burn that Retroleum rom, it will put some rainbow colors across the screen on boot, which might be a good alternative as you can also use it to check that the upper 32K is working when repaired. Even without a keyboard.

You can get a cassette adapter circuit cheap, and these take a SD card and there's about 10,000 games/programs on archive.org for the ZX Spectrum in TAP and zipped TZX format. There's a large archive you can download, but be warned you will need to break them up by first letter, and then you will have to break up some directories by first letter twice, because they are too big for the tape player... look up TZXDuino on Ebay and other sites. They are cheap.

I've never tried the DIVMMC, but should get one and will if I ever see a cheap one.

Sorry I couldn't be of much help earlier. I had to make 10 posts before they took the posting restrictions off, so most of my posts hung around for days waiting for a moderator. :(

David.
Click to expand...
#cj7hawk I purchased a new keyboard membrane as soon as I saw your post. unfortunately after making the purchase I havent received a single email from retroradionics and they havent answered a single one of mine regarding the shipment of the item. In the past have they been bad at communicating?
 
I don't know. I rarely email them. In fact I'm not sure I ever emailed them. Generally I just hand over my credit card details and the items come a few weeks later in the post.

They have been reliable and consistent in my experience, but I can't really comment on their communications. Normally I receive one email about 2 days after purchase, saying "Your order has shipped" with a tracking number via China Post. Then it's just a void until the package arrives. Though once that comes, it includes a link to the order number, and you can access their site as well to examine older orders.

Their packaging was always OK, but lately, they've taken extra steps to box things nicely, so I can't complain about how things arrive. Seems I'm going through quite a few keyboard membranes lately, and already need to order some more. Now I have to work out what to do with all of these older Spectrums I've been repairing for fun.

There might be a communications issue or language based issue. Whenever I see posts about what they are doing, they always come from others talking about them, not from them directly.

David
 
Might be related to Chinese New Year. That can disrupt a lot of commerce until mid-Feb. Otherwise I don't know. Has it been more than 2 days since you ordered?

You should be able to log in if you remember your order number and find out the status.
 
That is good to hear.

I've noticed yesterday that all of the shipping estimates from China are back to normal on other sites, so it's my guess that this was the cause, but it's still only a guess. Hopefully it will reach you quickly.

David.
 
So the new Coil from the UK seller arrived this evening. Pretty quick I must say. Just put it in the machine and fired it up. Quiet as a mouse. I cant hear a single thing. What an improvement. I highly recommend this eBay seller.

I think It must have blown a 4116 ram chip as I get random black squares now on the screen. I moved a few chips around and that makes it better so Ill have to go through them again. No big deal.
Still waiting on the keyboard membrane.


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