ZX Spectrum +2 (issue 3 – Grey version) Re-Cap and Heatsink Modification

March 02, 2022

ZX Spectrum +2 (issue 3 – Grey version) Re-Cap and Heatsink Modification

In this entry, I am performing a complete re-cap of an issue 3 Zx Spectrum +2 (grey) from start to finish. Included in the entry are the locations of the capacitors in question as well as locations of the vias for de-soldering.

Components required for this mod are:

4 X 1uF 50V Electrolytic Capacitors

1 X 4.7uF 25V Electrolytic Capacitor

1 X 10uF 25V Electrolytic Capacitor

5 X 22uF 25V Electrolytic Capacitors

2 X 47uF 25V Electrolytic Capacitors

2 X 100uF 25V Electrolytic Capacitors

2 X 220uF 16V Electrolytic Capacitors

A 40 pin thermally adhesive heatsink

Heatsink compound

IPA Alcohol

Solder

Tools required:

Soldering Iron

Cutters

Pilers

De-Soldering Gun or tool

Screwdriver

Solder wick (advisable but not necessary)

Toothbrush

Cotton Buds

The re-cap is pretty straightforward although I did have a couple of issues; firstly I had a dilemma with C62 which had a 100uF capacitor fitted yet the kit I bought had a value of 220uF for that capacitor.

And

I also had issues with my de-soldering gun blocking up for the first time.

As well as the re-cap, I thoroughly cleaned the PCB with IPA alcohol as this is the last modification I am doing on the circuit board.

Finally I renewed the heatsink compound on the ULA chip and fitted a new 40 pin heatsink to the Z80 processor chip.

So let’s get started!

Firstly strip down the +2; I have explained how to do this in other entries but if you are struggling leave a comment and I’ll gladly help.

Before we start this mod it is a good idea to familiarise yourself with Electrolytic Capacitors. Below is a picture of a 10uF 25V Electrolytic. I have labelled all the relevant markings and features.

It is very important that you fit replacement electrolytic capacitors in the correct polarity. The ZX Spectrum +2 (issue 3) has very good markings on it which will tell you where the positive leg of the capacitor goes.

However manufacturers can still get things wrong as was seen when the factory fitted incorrect transistors into the same system so it is always good to check orientation before you replace.

A good way to check that you are fitting the replacement capacitor in the correct orientation is to take pictures and also do them one at a time (this should also ensure that you fit the correct value of capacitor)

Faulty electrolytic capacitors are usually easy to detect; if they are in the process of ‘blowing up’ you may see a bulge on the very top ‘aluminium’ part of the capacitor. Other tell-tale signs are leakages of electolyte at the base of the capacitor; again this is easy to detect with a simple visual inspection.

A quick visual inspection showed no signs of damage to the capacitors on the +2

But, that doesn’t mean that the capacitors are in good working order.

I decided to start the mod from left to right on the PCB and the photos below will show you the order that I replaced them in.

Starting with C81; it is a 100uF 16V electrolytic and its location can be found below

But for de-soldering purposes, we really need to know which vias (pads) to de-solder so I have highlighted them in the photo below.

I will go over the whole de-soldering practice with you on this capacitor (including problematic capacitors)

To help you de-solder, it is a good idea to add fresh solder to the original solder joints. This adds flux and should make reflowing the solder a whole lot easier.

Another good tip is to add flux to the solder joint before soldering; personally I like to see how things go before adding flux simply because it is messy and sticky!

Now it is time to desolder:

You will need some kind of de-soldering tool; one of my most recent additions to my workshop area is a De-Soldering Gun which I am extremely happy with. But I know that they are expensive and not everyone can justify the expense (you can pick up a cheap de-soldering tool as seen in my earlier entries for a couple of pounds on ebay)

De-solder the two highlighted vias.

Once de-soldered, carefully remove the capacitor (watch for any physical resistance when pulling it from the PCB) If need be, add fresh solder to the vias then try the de-soldering process again. In some instances, I found that I had to use my soldering iron when pulling the capacitors from the PCB.

Once removed, solder in the replacement 22uF capacitor ensuring that you place the capacitor in the correct orientation.

Once soldered, trim the legs of the capacitor just above the solder joint with your cutters.

The remaining capacitors are done in exactly the same way so I will just highlight the locations of the capacitors and vias in the order I replaced them in.

Next up is C29 which is a 1uF 50V Electrolytic Capacitor, below is the location of the capacitor on the component side of the PCB and below that the location of the vias.

The next capacitor I replaced was C5 which is a 220uF 16V Electrolytic Capacitor.

C68 caused me some confusion as I had a 100uF capacitor on my PCB yet both the schematic diagram and capacitor kit suggested that this was a 220uF 16V.

I replaced it with a 100uF capacitor to begin with then after a bit of reading replaced that with a 220uF 16V capacitor.

C6 was next which is a 100uF 25V Electrolytic Capacitor.

Then I replaced C49 which is a 1uF 50V.

Next up was C50 which is also a 1uF 50V capacitor.

Then I replaced C36, again a 1uF 50V Cap.

After that I turned my attention to C39, a 4.7uF 25V Capacitor.

Then I replaced C41, a 100uF 25V Electrolytic Capacitor.

C30 was next which is a 47uF 25V Capacitor.

Followed by C23, a 22uF 25V Cap.

C25 was next which is a 47uF 25V Capacitor.

Then C24, a 10uF 25V Electrolytic Capacitor.

C62 was next on the list which is a 22uF 25V Electrolytic Capacitor and I found that it was quite awkward to de-solder.

I then replaced C63, also a 22uF 25V Cap and had a similar problem de-soldering it.

Then I replaced the 100uF capacitor fitted for C68 earlier with a 220uF 16V capacitor.

The final capacitor in the Capacitor kit was C52 which was originally a 22uF 25V Electrolytic Capacitor. As I had replaced that capacitor with a 100uF 25V Capacitor during my Jailbar and Ghosting Fix (see earlier entry) I decided to leave the 100uF Capacitor in place. If you require to replace C52, I would recommend replacing it with a 100uF 25V as this will help to improve the picture quality of the video on your TV set.

Locations can be found below.

After replacing all the Electrolytic capacitors and with no further plans to repair or modify the circuit board, I gave both the solder side and component side of the PCB a good clean with some IPA Alcohol and a toothbrush.

Cleaning the solder side of the PCB with IPA and a toothbrush does remove (or loosen) flux residue left over from soldering both new soldering and factory soldering. However it does leave a sticky residue all over the PCB. I found that the best way to remove the mess was to use some fresh IPA and a cotton bud.

After I thoroughly cleaned the PCB, I turned my attention to the heatsink on the ULA. As the ULA for the ZX Spectrum +2’s are quite rare and expensive to replace, it is a good idea to replace the old heatsink compound on the heatsink and ULA.

To remove the old heatsink, I gently twisted the aluminium clip with a pair of pliers then lifted it from the ULA IC.

I am very glad that I decided to do this wee modification as there was hardly any heatsink compound on the ULA or heatsink at all as can be seen in the photo below!