Help me fix my grail ZX 128k Spectrum

Beaps · July 2014

Hi all,

Ok today my grail toaster rack ZX spectrum 128k turned up. I finally found one and for a reasonable price. I powered it up and..... Nothing

I checked the voltage on the 5v rail and nothing.

Anyone got any pointers on where to start to maybe try and fix this, or can anyone fix it for me for a fee?

balford · July 2014

Ok, first things first. No voltage on the 5v rail would either indicate a regulator failure or a PSU failure.

Verify that you've got power coming from the PSU, and also check that the connector from the motherboard to the regulator on the heatsink is attached the right way round - someone could have been messing with this and not put it back correctly!

If all this checks out, try replacing the regulator with a 7805 or 78S05.

B

zedexspectrum · July 2014

deleted i should read properly first.

Beaps · July 2014

I am using a grey power supply that came with my +2. It says Sinclair on it and has the vents/grill on the right. I know this workd as I have tested it on the +2

balford · July 2014

Perfect, a grey +2 PSU can be used on anything from a 48K up (I used one for all my machines until I got a modern regulated 9v supply).

Sounds like either the regulator has failed or the connector was incorrectly replaced.

The 9v supply should be present on pin 1 (leftmost looking at the top of the regulator), and you should see 5v on pin 3.

B

Beaps · July 2014

I am a novice at this kind of stuff, can you explain what a regulator is lol

1024MAK · July 2014

It converts a raw dc supply (with a voltage greater than the wanted final "output" voltage) to a nice smooth regulated stable supply voltage suitable for the sensitive electronic circuitry like a Z80 CPU.

In a toastrack Spectrum 128k, it is mounted on the black metal heatsink on the right hand side of the machine. It will have the type number "7805" written on it (the number will normally be in the middle of other letters and sometimes numbers).

The pins, looking left to right with the metal tab (that is bolted to the heatsink) at the top are numbered 1, 2, 3. With the left hand pin (pin 1 ) being the input, the middle pin (pin 2) being the 0V/common/ground) and the right hand pin (pin 3) being the output (for a 7805, this is +5V).

If you want, I can post some pictures, just give me a bit of time to process them...:D

Mark

Beaps · July 2014

Ok I found that, seems simple to replace. Where can I pick one up maplins or any eBay links.

balford · July 2014

Check to see that it's defective first :)

With your multimeter, place the ground probe on the middle pin and check the voltage on pin 1 (left), this should be above 9v. Be careful not to short the probes!

Once 9v is confirmed, repeat the measurement except with pin 3 (rightmost). You should see almost exactly 5v on this.

If the above is what you see, then the regulator is fine.

Try this first and report back :)

B

Beaps · July 2014

I did test this and I got nothing on the multimetre. I put the black probe on the middle black wire and red probe on the red wire

1024MAK · July 2014

Beaps wrote: »

Ok I found that, seems simple to replace. Where can I pick one up maplins or any eBay links.

Whoa there. First, safety first :grin:. No not your safety (there are no hazardous voltages to humans in a Sinclair ZX Spectrum 128k+ toastrack). The safety of the circuitry :-).

Whenever poking about on boards that have power applied to them, ensure that you do not accidentally short out any connections. It is very easy to move slightly and then as a result your meter probe / logic probe / 'scope probe can move and short between adjacent pins. So be careful ;-).

Now, in order for us to help you, it would be helpful if you can report back your results :).

I presume you know that on digital electronics like the Spectrum, all voltages are taken with respect to 0V/ground?

So what voltage do you get on the lead connected to the 7805 regulator pin 1 (the input)?
What voltage do you get on the lead connected to the 7805 regulator pin 3 (the +5V output)?

Mark

Beaps · July 2014

OK here is what I tried

balford · July 2014

So no +5v measured from the points indicated on your picture?

Try measuring +9v from the leftmost point (blue wire), leaving the black probe in the middle position.

If you get +9v from here, then the regulator is most likely toast.

If you don't, and you've already checked and verified the power supply, then it could be the power socket at fault.

Maplins do carry replacements for both, but let's see what's broken first :)

B

Beaps · July 2014

Let me test the 9v hold on

Beaps · July 2014

OK it says 27.3 on the +9v :confused:

Beaps · July 2014

This is the setting on the MM

1024MAK · July 2014

You need to use a DC range (marked with a solid line and underneath a dashed line). You picture shows your meter set to measure AC voltage, which is not what we are trying to measure.

Mark

1024MAK · July 2014

Use the 20V DC voltage range on the top left of the selection switch.

Then test pin 1 and pin 3 of the regulator again...

Beaps · July 2014

12.82 on that setting

Beaps · July 2014

still nothing on pin 2 (black) with pin 3 (red)

Beaps · July 2014

Can I say THANKS to all so far for your input so far.

balford · July 2014

Ok, I think it's safe to call this a regulator failure so :)

You can pick up a replacement from Maplins, here's what you need.

Pick up some thermal compound while you're there and smear a bit between the heatsink and the regulator when you're fitting the new one.

You don't even have to do any soldering :) Just make sure that you replace the connector to the regulator the right way round when refitting.

A word of caution - this may either fix your problem, or bring us one step closer to getting it working by removing one of multiple faults. So don't get your hopes up.

B

Beaps · July 2014

OK I will head out to Maplins & report back later today.

1024MAK · July 2014

After removing the old 7805 regulator, clean the area on the heatsink where the regulator was fitted, so there are no dried up areas of old grease left.

Then apply a thin smear of thermal grease to the metal tab of the new 7805 regulator. The idea of the thermal grease is to fill in any small holes and voids with heat conductive grease, thereby displacing the air from areas where pockets of air would otherwise be present.

What is not wanted is for a large amount of grease to form a thick sandwich which prevents the metal of the regulator from touching the metal heatsink.

Do the mounting screw up nice and tight. In order for the 7805 regulator to work correctly, it has to be able to transfer the heat that it generates to the heatsink :).

Good luck :-) and welcome to the world of electronic repair :grin:.

Do let us know how you get on 8-).

Mark

Beaps · July 2014

Ok I rushed out the house to maplins, asked for the regulator, got a few screwed up faces, so I showed the link 8) 'oh this one' lol

Legged it to my chav pc shop and bought some grease. Followed the above instructions and....... It's works (I am doing the splits & moonwalk right now)

The only problem I have now is the down arrow on the main screen don't work, up arrow key and enter work tho?

balford · July 2014

That'll be a new membrane required in that case. Pretty much par for the course for any 48/128 machine (I factor in the cost when buying by default).

Here's what you need, replacement is fairly straightforward.

Congratulations on the repair :)

B

1024MAK · July 2014

Well done :-)

Beaps wrote: »

The only problem I have now is the down arrow on the main screen don't work, up arrow key and enter work tho?

Do you mean that the down arrow key does not work?
Try instead pressing CAPS SHIFT and "6" at the same time. It could be a fault with the keyboard membrane.

Mark

Beaps · July 2014

How do you get the volume right to load games, it's very difficult lol?

How do I bring up that tape tester program

balford · July 2014

Are you using real tape or MP3 playback?

If real tape, what type of recorder is being used?

If MP3, are you using an iPod/smartphone/tablet, or a laptop/desktop?

This thread may be helpful.

B

Beaps · July 2014

I am using TZX2WAV.

I just hooked up my laptop to test & it loaded but I want to use my iPod. I tested my iPod but I think the volume on max is still to low. How do I boost the volume on the iPod

balford · July 2014

You might need an intermediate amplifier to boost the signal a little.

As I use the headphone output on my PC speakers for external game loading, I'll defer to others with experience in this area :)

B

Help me fix my grail ZX 128k Spectrum

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