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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 27th Jan 2020, 2:10 pm   #1
Paulus.d
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Default ZX spectrum +2

My long run of technical bad luck continues with the destruction of this computer after several month's of work getting it connected to a modern TV.

I made a lead up to go from RGB to SCART, connected it .it was great ..so sealed it up and thought I would try to add a socket for audio in to use with a separate cassette machine.

On powering to test it , L4 went up in smoke and I seemed to have killed the power brick...no 12 or 5v...

I'm thinking of leaving the retro world and ditching all of it ...

Regards Paul
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Old 27th Jan 2020, 10:15 pm   #2
Superscope
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Default Re: ZX |spectrum +2

Hi Paul,

Don't give up on it.
We have all been there. Trying to keep vintage Equipment going, only to inadvertently Damage it more than it was before we got it.

Not quite sure how adding an Audio Socket would have caused that issue,
I guess you probably had a Short Circuit on the connector somewhere.

The important thing with a catastrophe like you mentioned is:
Did you learn by it ?
and if the answer is Yes, it is not all bad.
That's the way I look at it.


Ian
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Old 28th Jan 2020, 8:10 am   #3
mervyn
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Default Re: ZX |spectrum +2

Hi Paul
As Ian has said , learn from it
Most of my learning has been from screwing stuff up and sorting it out
Also most of the Spectrum stuff is easy to get bits.. stick with it

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Old 28th Jan 2020, 11:22 am   #4
Paulus.d
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Default Re: ZX |spectrum +2

thanks guys...… I needed that ….
I may have shorted the RGB lead when closing the ends up ...there is +12v present there ..
regards paul
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Old 28th Jan 2020, 11:26 am   #5
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Default Re: ZX |spectrum +2

Quote:
Originally Posted by Paulus.d View Post
thanks guys... I needed that .
I may have shorted the RGB lead when closing the ends up ...there is +12v present there ..
regards paul
It happens. I have just destroyed an Arduino and an expensive display because a Veroboard strip wasn't properly cut. I couldn't even see the join with a magnifier, it was the meter that finally found it.
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Old 28th Jan 2020, 12:01 pm   #6
paulsherwin
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Default Re: ZX spectrum +2

We've all done similar things, it only takes a moment's inattention. I once blew 4 valve filaments by inadvertently shorting out a 7805 in the power supply. You won't make the same mistake again.
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Old 28th Jan 2020, 5:54 pm   #7
els1967
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Default Re: ZX spectrum +2

I've wrecked at least 5 arduino's, one mega. Also quite a rare IC for the speakjet voice synth and the speakjet itself as well as a DTMF IC just trhough a short on the verobaord for the 24v supply. Well over 100 of equipment I would think. More LED's and ESP8266's than I can remember.

I live and learn. Well, I mean I live...
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Old 28th Jan 2020, 7:16 pm   #8
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Default Re: ZX spectrum +2

Getting back to the Spectrum +2, does anyone know an online source for the Spectrum +2 diagram? If we know where L4 is in the circuit we may be able to suggest avenues for exploration.

L4 is most likely in series with one of the positive supply rails, and if it has gone up in smoke the chances are that the modification somehow ended up shorting that rail to 0V.

This is not the worst thing that could happen, overvoltage or reverse polarity would be far worse.

Edit: Supplying my own answer, here is the service manual for the +2 (I assume original +2, not the Grey 'Amstrad' +2A?)

https://spectrumforeveryone.com/wp-c...viceManual.pdf

Last edited by SiriusHardware; 28th Jan 2020 at 7:22 pm.
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Old 29th Jan 2020, 8:07 am   #9
mervyn
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Default Re: ZX spectrum +2

http://retroisle.com/sinclair/zxspectrum/technical.php
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Old 29th Jan 2020, 9:00 am   #10
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Default Re: ZX spectrum +2

Going by Pauls post mentioning losing 12v and 5v from the power supply, I assume you have the black case +2 which is the +2A/B model which have large power brick psu. Here's schematics for those models.

https://zxnet.co.uk/spectrum/schematics/

Cheers, Steve.
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Old 29th Jan 2020, 9:21 am   #11
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Default Re: ZX spectrum +2

And here is schematic for the power supply.

http://hardware.speccy.org/hardware/...squemas-i.html

Cheers, Steve.
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Old 29th Jan 2020, 5:22 pm   #12
Paulus.d
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Default Re: ZX spectrum +2

yeah ...it's a black one ….
either short to 0v or one of the RGB lines …


I'm gonna get the power brick working again then check the +2 out and see what it's done.

The L4 will be dead ..I heard it crack!!!
Regards Paul
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Old 29th Jan 2020, 7:07 pm   #13
SiriusHardware
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Default Re: ZX spectrum +2

The purpose of L4 is to prevent interference from travelling from the supply rail into the audio sub-carrier circuit and also to prevent interference from travelling out from that part of the circuit and onto the supply rail.

For diagnostic / testing purposes you can replace it with a wire link or very low value, low wattage resistor and then once you have the machine essentially working again, seek out a replacement for L4. If you do that, however, you first need to be sure that there is no longer a short between the 'bottom' end of L4 and 0V.

Probably the easiest place to measure for a short would be between pin 8 (+5V) and pin 1(0V) of the MC1376 IC. If you find a short there, find the cause of that short and then replace L4 (temporarily) with a wire link or very low value resistor.

The audio socket modification you did, was that of your own devising or was it from an online how-to somewhere? If the former, can you post details, if the latter, please post a link to the modification guide you followed.
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Old 29th Jan 2020, 8:45 pm   #14
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Default Re: ZX spectrum +2

If it is any consolation while recently trying to help find a fault on the Spectrum Next expansion bus with the Interface 1 and Microdrive, I was comparing waveforms between my 48K with IF1 on it (out of its case) and when in the Next - had some tape isolating so the hook pins didn't short, I didn't notice with the constant movement I had worn a hole in the tape - 12V onto the WAIT line seems to have had a significant effect on the IF1 and 48K Issue2 machine - I count myself lucky as the VDrive and Microdrives hooked up survived. I now have a third Issue2 board in the pile for repair and an IF1...

It is all part of the experience like the time we ended up fitting a 1600 head gasket kit to an 1800 Mondeo...

The cost was also worth it as anyone who wants can now use the IF1 and Microdrive on the Next...

https://youtu.be/EU9NTQqQ1fg
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Old 30th Jan 2020, 12:44 am   #15
SiriusHardware
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Default Re: ZX spectrum +2

I really must try out my vDrive, I've had it since the middle of last year. It was one of those things I didn't have an immediate need for but I thought I'd better get one while they were available as things like that are often only produced in a few batches and then never again. Nice to see one working.

The NEXT seems to be coming along nicely as well.
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Old 1st Feb 2020, 1:42 pm   #16
mervyn
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Default Re: ZX spectrum +2

i have here an old ZXL print interface for spectrum and also a technology research spectrum disc interface for spectrum.. If any good for you i'll drop them off sometime
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Old 1st Feb 2020, 6:35 pm   #17
SiriusHardware
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Default Re: ZX spectrum +2

It's not clear who you are addressing your comment to, mervyn, but I'm sure there won't be any shortage of people interested in your Spectrum items. Edit: I guess you meant Paulus.d, since you are apparently both in Kent.

The disc interface sounds especially interesting, presumably that interfaces to a (then) standard 5.25 floppy disc drive?
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Old 2nd Feb 2020, 7:04 am   #18
mervyn
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Default Re: ZX spectrum +2

yes sorry about that. yes Paul D , but if he does not have use for it then if anyone else wants them please ask
regards
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Old 2nd Feb 2020, 6:55 pm   #19
Paulus.d
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Default Re: ZX spectrum +2

Thank you for thinking of me with the items....... i'mnot really interested as I don't have a working Spectrum to use them !!
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Old 5th Feb 2020, 11:46 pm   #20
Timbucus
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Default Re: ZX spectrum +2

Mervyn - I would find the BETA disk handy if you still want it to come to a good home as mine from BITD is fried and I have a few disks formatted on one I would like to recover if the offer is still there? I would also like to test it with the Next as well as it should work.

Sirius - it is, the actual units started shipping this week so can't wait to get mine they look stunning...

https://www.youtube.com/watch?v=iLDz...oXMk8-B0wphihI

need to get back on the MK14 core then... would be ideal on this.
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