Harlequin rev g - assembled but not working

A place to discuss the ZX80's and ZX81's younger brother - the Sinclair ZX Spectrum
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snikolaenko
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Joined: Sat Jul 02, 2016 8:41 pm

Harlequin rev g - assembled but not working

Post by snikolaenko » Sat Jul 02, 2016 8:56 pm

Hello Everybody,

Not sure if anybody is able to help but I hope so :)

So I assembled Harlequin rev g. Everything is in place, all jumpers are in the right position, but nothing is happening at startup. Nothing at all. I can see some signal coming into TV, because the grey screen changes its color a bit when I plug in composite connector. All I was able to test myself is the right voltage is coming from voltage regulator and the same voltage is present at CPU, ROM and a few other components (didn't check all of them).

My knowledge of electronics is very basic so I'm not even sure where to start. Is there a chance to get it working at all, if say I screwed something up while soldering components? Can some sort of troubleshooting be done by a rookie or would it require a great level of knowledge and special equipment?

One simple question to finish the post: does ZX Spectrum beep at startup? Mine doesn't produce any sounds.

Thanks a lot!
Sergey

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: Harlequin rev g - assembled but not working

Post by 1024MAK » Sun Jul 03, 2016 10:37 am

We need more information if we are to help you.

The ZX Spectrum does not beep at start up. It should however produce the key "click" buzz when it senses a key on the keyboard being pressed. If you don't have a keyboard connected, simulate a key by using a wire to briefly link one contact in the left hand keyboard connector and one contact in the right hand keyboard connector.

The most likely fault on your board is a poor solder joint, or a pin and pad that you have missed and not soldered. So under a good light, carefully examine each and every pin / pad connection on the underside of the board. Use some Isopropyl alcohol (IPA) in a well ventilated space to clean off the flux from the board.

What type of solder did you use?
For the 60/40 tin/lead solder, the solder should be shiny, not dull. Each pin/pad should have smooth sides with the solder having flowed all the way around the pin with no lumps or bumps and no missing sections. Use a search engine to find a "good soldering guide".

The lead free solder is harder to use, but if you are practised, you can still get good results. The appearance is slightly different to the 60/40 tin/lead type though.

For fault finding, pictures of both sides of the board and of the TV picture may help.
Apart from a meter (what type of multimeter are you using?), what other test gear do you have?
If you don't have anything else, it is worth considering buying (or making) a logic probe, so that you can see the state of the digital signal pins.

Mark

snikolaenko
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Joined: Sat Jul 02, 2016 8:41 pm

Re: Harlequin rev g - assembled but not working

Post by snikolaenko » Sun Jul 03, 2016 5:37 pm

Thank you Mark!

Will do exactly as you said. Will start from simulating a keyboard and cleaning the underside of the board with IPA (why am I thinking of India Pale Ale? :) ). Will then take a picture and post here.

To your other points. Yes, soldering may be a problem. It's my first project with tiny pads and I possibly did something wrong. Hoping to check after cleaning the board. I did watch lots of soldering videos and practiced before I started with harlequin, but yes, some joins look ugly. But I'm not giving up :)

I used 60/40/tin/lead type of solder and entry level soldering station.

As for equipment, I have nothing but the cheapest possible meter. I don't mind buying or building a logic probe. Depending on budget of course. Can you please provide more details/suggestions on what is needed?

Thanks a lot for your help! I really appreciate it!

Sergey

snikolaenko
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Joined: Sat Jul 02, 2016 8:41 pm

Re: Harlequin rev g - assembled but not working

Post by snikolaenko » Mon Jul 04, 2016 2:09 am

Ok. Of course I was stupid enough and missed entire side of one IC. And I swear I checked everything many times before... of course I did. Thanks a lot to Mark for suggesting to do it once again!

But the story doesn't end here. After I fixed that issue, the screen finally showed something. But that something was just a bunch of blinking color squares. I'm attaching the picture. The picture is the same regardless of ROM being inserted or not. I'm using ZX diagnostic ROM.

If the picture gives no clues, I will have a fresh look at the board tomorrow once again and clean it with isopropyl alcohol. Bought one already.

I'm also attaching a picture of the board itself in case there may be some clues. The picture of the underside will follow after the cleaning is done.

Thanks a lot!
IMG_20160703_174414557.jpg
IMG_20160703_174414557.jpg (3.4 MiB) Viewed 469 times
IMG_20160703_174404135.jpg
IMG_20160703_174404135.jpg (3.24 MiB) Viewed 469 times

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1024MAK
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Location: Looking forward to summer in Somerset, UK...

Re: Harlequin rev g - assembled but not working

Post by 1024MAK » Tue Jul 05, 2016 1:26 am

It looks like the Z80 CPU is not running. More tomorrow (it's late and I'm tired).

Mark

snikolaenko
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Re: Harlequin rev g - assembled but not working

Post by snikolaenko » Tue Jul 05, 2016 8:03 pm

Thanks and no worries. I've been busy too it's all understood. Appreciate your help.

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