Trying to fix my ZxSpectrum+

For experts to discuss very technical stuff and newbies to ask why the Spectrum they bought off ebay doesn't work.
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1024MAK
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Re: Trying to fix my ZxSpectrum+

Post by 1024MAK »

Note that before fitting any sockets or components, recheck your work, at least TWICE. Use a good multimeter on the continuity range to prove that every pin on every chip/component is connected to everywhere it needs to go. Not just to the next nearby chip or component.

I suggest you print out a schematic diagram (relevant to your board issue number) on paper, and mark each pin on each component with a coloured pen. Just beware that for ease of routing the tracks, address lines and data lines may not run exactly as shown in the schematic. Also beware that the schematics have some errors.

If you have problems, stop work and ask on here.

When fitting the sockets, where you have a good pad with the through-hole plating intact, it is just a case of soldering the pin of the socket (and any wire). Where the pad is missing, or the through-hole plating is missing or damaged, carefully and neatly wrap the wire(s) around the pin of the socket, then solder the wires and the pin to ensure a good electrical connection. The resulting joint will not look like the normal joints, as the solder can’t flow in the same way compared to when there is a PCB pad.

After soldering, you should clean off any flux residue. Use a suitable cleaning system appropriate to the type of flux in your solder (the solder should be lead based 60/40). Water soluble flux can be cleaned with tap water. Other flux types should be cleaned with either flux cleaner, or IPA (the solvent, not the drink). The cleaner will dissolve the flux, but gentle rubbing with a toothbrush (use a new clean one, as you don’t want to put this one in your mouth!) helps to remove stubborn residue. Now over a suitable container, flood wash the area of the board that you are cleaning, while holding it at a 45o angle.

Once the sockets are fitted, don’t get carried away and fit any replacement memory yet. First, power up and test the -5V, the +12V and the +5V power rails in that order. If any are out of specification, turn off immediately.

Once you are happy that the power section is okay, switch off, then you can go head and fit the replacement memory.

Then it is time to power up and test it ;)

Mark
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1024MAK
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Re: Trying to fix my ZxSpectrum+

Post by 1024MAK »

While we are on the subject of repairs to old computers, unless you have a lot of experience and have good quality desoldering equipment, often with most components and chips, the PCB is more valuable than the component or chip. So it’s a good idea to use a method which is as kind to the PCB (board) as possible.

So if replacement components or chips are available, it is far easier to use a fine set of electronic snips (wire cutters) [NOT the large type used by electricians] to cut the component legs/leads one at a time. With DIL/DIP chips, cut the legs as near to the plastic body as you can.

Once the body of the component or chip is removed, you can then heat up each pad one at a time, and once all the solder is completely molten, pull the remaining bit of leg/lead out with fine line nose pliers or metal tweezers. One all the remaining bit of leg/lead have been removed, use a desoldering pump, to clear the solder from the holes. Desoldering pumps work best when the tip is pressed up against the board to minimise the gap that air can enter from the sides.

Obviously the above method is not suitable for removing rare, hard to get or expensive good working chips or components from a board!

It is wise to fit quality sockets and then put the chips in the socket, rather than soldering the replacement chips directly back on the PCB. However there are exceptions (mainly if the chip uses the pins to get rid of heat, such as power transistors, diodes, regulators and audio output amplifiers, or in very high frequency applications).

Mark
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma »

Thank you mark! As regars schematrics diagram i found this:

https://spectrumforeveryone.com/wp-cont ... matics.gif

But where i can find some schematics to restore the track of RAM that i have broken?

i only found this:

https://k1.spdns.de/Vintage/Sinclair/82 ... 0blank.jpg

but it's too small image
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1024MAK
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Re: Trying to fix my ZxSpectrum+

Post by 1024MAK »

As far as I know, there are no drawings showing the track layout for ZX Spectrum 16K / 48K / plus boards.

There is a pin-out of the 4116 (or equivalent) DRAM chips over on Sinclair ZX World.

All the pins with the same name on each chip are linked together and then go to various places (see the schematic for further details), except for pin 2 (‘D’) and 14 (‘Q’). For each DRAM chip these two pins are linked together, then each line goes to one of the 470 ohm resistors (R1 to R8) and also to the D0 to D7 connections on the ULA (pins 18 to 31, but see the schematic diagram).

Mark
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Muttley Black
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Re: Trying to fix my ZxSpectrum+

Post by Muttley Black »

If you have a magnifier, it is really easy to locate the path from the broken traces. Sometimes even with no magnifier you can see that. But as Mark said...
1024MAK wrote: Sat Jun 08, 2019 1:34 pm All the pins with the same name on each chip are linked together and then go to various places (see the schematic for further details), except for pin 2 (‘D’) and 14 (‘Q’). For each DRAM chip these two pins are linked together

Mark
...thats mean for example, that Pin 1 from IC13 should be connected with pin 1 of IC6, but through ALL pin 1 he find in his way. Same thing for pins 3,4,5,6,7,8,9,10,11,12,13,15, and 16. Except pin 2 and pin 14 that are linked together on each dram chip ONLY! I am sure you can understand that, even if you look on your own photos. If you can see that, you can imagine also the paths of your broken traces.

One last think is forget about paths of traces from pin1, pin8, pin9 and pin16. You dont have a damage there, cause that traces are not the same type, of the traces you damaged, or the traces are only visible from the solder side of the board, but it is good move to test the continuity to be sure.
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Morkin
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Re: Trying to fix my ZxSpectrum+

Post by Morkin »

1024MAK wrote: Fri Jun 07, 2019 12:11 pmOther flux types should be cleaned with either flux cleaner, or IPA (the solvent, not the drink).
:lol:
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma »

Ok, on the next weeks i'll buy some new equipment to repair this damage. I will keep you informed on how it is proceeding. For now thanks to all! 8-)
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma »

Hi guys, a little update. With a software I designed the lower ram pcb scheme to be sure not to make mistakes later when I try to restore the tracks. Did I do everything right? Thanks in advance for every reply.

Image
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma »

Hey guys, it's been a bit that I didn't update my post. Here some news:


Image

Image

I put all the 7 sockets!!!!! And I'm very proud of me guys!!! Now I've a doubt, I dunno where to solder this pin:


Image it's near the blu capacitor..
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DouglasReynholm
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Re: Trying to fix my ZxSpectrum+

Post by DouglasReynholm »

Well while I'm sorry I can't help you much here, as the person that sent you here from another social media site (shhhh!), I'm impressed with the effort you are persisting with to get it fixed.
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma »

I think it should be connected to the pin 14 of IC7, but i'm waiting some confirm! :D
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Ast A. Moore
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Re: Trying to fix my ZxSpectrum+

Post by Ast A. Moore »

I only have a picture of a populated Issue 6A board, but it’s fairly high resolution. The trace form that via goes up and is likely connected to the via next to Pin 3 under the socket. It’s best to use the schematic and a tester in continuity mode and determine the exact routing by process of elimination.

Still, I hope this picture will help you:

Image
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Muttley Black
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Re: Trying to fix my ZxSpectrum+

Post by Muttley Black »

Hyuma wrote: Mon Jul 01, 2019 8:12 pm I think it should be connected to the pin 14 of IC7, but i'm waiting some confirm! :D
Yes. I confirm that.

Also, clean your work with isopropyl alcohol and toothbrush before you test the unit.
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma »

yes, now next step will be buying rams and ZTXs
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma »

Time for some updates, 751 and 651 are in place!

Image

Image

Can i do some tests now? (I still don't have ram)
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma »

With multimeter in continuity mode i got:

ZTX 651 values:
670, 671, 1, 1

ZTX 751 values:
670, 668, 1497, 1
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma »

I power on without ram for some seconds and the screen is bit better then before. THERE IS STILL LIFE! :D :lol:

Now with new ZTX 651 and 7651 (without new RAMS)
After some seconds I pressed the reset button and this is result:

https://imgur.com/a/Se0bVKu


this was before:

https://imgur.com/raae8HW
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Ast A. Moore
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Re: Trying to fix my ZxSpectrum+

Post by Ast A. Moore »

Looks like the CPU can fetch and execute the first few instructions, including a jump, from the ROM, which is great news.
Every man should plant a tree, build a house, and write a ZX Spectrum game.

Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma »

Ast A. Moore wrote: Tue Jul 09, 2019 11:38 am Looks like the CPU can fetch and execute the first few instructions, including a jump, from the ROM, which is great news.
Wow! I'm really, really, really happy today! Next step will be RAM!
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1024MAK
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Re: Trying to fix my ZxSpectrum+

Post by 1024MAK »

Hyuma wrote: Tue Jul 09, 2019 10:43 am Can i do some tests now? (I still don't have ram)
Sure! :D

Test the voltages on pins 1,8 and 9 in the position where IC6 was (or any other of the 4116 or equivalent DRAM chip positions). With the negative probe to 0V/GND (e.g. the case of the modulator or the heatsink).

Expected voltages:

PIN 1: between -4V and -5.5V
PIN 8: between 10.8V and 13.2V
PIN 9: between 4.75V and 5.25V

If all these are good, then the next stage is to sort out the ‘lower’ DRAM chips.

Mark
:!: Standby alert :!:
“There are four lights!”
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :dance
Looking forward to summer later in the year.
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma »

1024MAK wrote: Tue Jul 09, 2019 3:57 pm
Hyuma wrote: Tue Jul 09, 2019 10:43 am Can i do some tests now? (I still don't have ram)
Sure! :D

Test the voltages on pins 1,8 and 9 in the position where IC6 was (or any other of the 4116 or equivalent DRAM chip positions). With the negative probe to 0V/GND (e.g. the case of the modulator or the heatsink).

Expected voltages:

PIN 1: between -4V and -5.5V
PIN 8: between 10.8V and 13.2V
PIN 9: between 4.75V and 5.25V

If all these are good, then the next stage is to sort out the ‘lower’ DRAM chips.

Mark
pin 1: -5,21v
pni 8: 12,38v
pin 9: 4,98v

yesssssssss! :lol: :lol: :lol:
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Muttley Black
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Re: Trying to fix my ZxSpectrum+

Post by Muttley Black »

Keep on walking! :)

-If it’s not problem for you, please use Postimage to upload your photos. It is easier as Postimage button is pinned on “reply” mode, but also is way better and safer for you photos to stay online for long time.-
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma »

I just noticed that retroleum website has lower ram module out of stock... damn!
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1024MAK
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Re: Trying to fix my ZxSpectrum+

Post by 1024MAK »

See here for another source of Lower RAM modules ;)
I have bought from here before and got good service :D

Mark
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“There are four lights!”
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Looking forward to summer later in the year.
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Re: Trying to fix my ZxSpectrum+

Post by Hyuma »

I sent an email to the guy of retroleum and he re-stock the item! I just bought 1 lower ram! Let's wait for it!
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