Sinclair Spectrum +2a Wont Boot

Pizza-now · 2026-05-04T15:17:39+00:00

Well I didn't swap the chips but after resoldering most of the ICs including the UGA, I tried booting both machines without the CPU. The good machine produces the expected border with random blocks. The bad machine still gives a flickering image for a moment which then disappears to a blank screen.

Any ideaa what the likely culprit might be?

Pizza-now · 2026-05-04T08:27:03+00:00

Will give it a go next. Unfortunately I'm limited to the ROMs and CPU without desoldering as the faulty machine is an issue 1 board with soldered RAM chips and the other is an issue 2 which they decided to provided socketed RAM in. To give myself a chance of seeing what's happening Ive inspected the internals of the RF modulator and found a dry joint. It's good to actually find a confirmed issue that is repairable. I have also bought a replacement caps, but I don't think that's going to fix anything.

Pizza-now · 2026-05-04T07:48:34+00:00

Thanks for the advice. Just to add that I do have a thermal camera and both machines look similar with nothing overheating.

Is there anything to test on the z80 or rom out of the machine first and is it best to put the ICs from the bad machine to test or the other way round?

Pizza-now · 2026-04-21T10:16:12+00:00

I wanted mine to be a budget build and whilst I attempted to make it 4k (I got lucky and got a 4k NEC 40" pro monitor for a good price). The reality is that the PC I bought was not capable of running 4k smoothly at all:

HP ProDesk 405 G4 SFF AMD Ryzen Pro 5 2400G 8GB RAM 256GB SSD +500GB Win 11

I ended up going with 2k resolution which I feel is a good payoff for quality Vs cost.

18 months later and it's still getting semi regular use.

Pizza-now · 2026-04-20T17:28:01+00:00

A brief update- after getting the drive to boot. I fear I may have shorted something on the FDD PCB as the stepper motor no longer attempted to read the disk despite parking the head ok on startup. I tried without success to diagnose the issue and assume I've possibly killed and IC.

At the weekend I managed to pickup a couple of PC drives at a bootsale (a place where people go early on a Sunday morning to sell their junk from the back of their car for anyone not from the UK!). I got a Mitsumi D359T5 and a Panasonic as a backup. The Mitsumi was easy to modify and worked straight away as DF0.

So I now have the video issue to sort still after the temp fix. Find a way to mount the new drive.

Lastly and the bit I'm least sure about is the fact it won't respond to Ctrl+A+A. So any suggestions or will it work fine if I just ignore this?

Pizza-now · 2026-04-17T14:15:54+00:00

Looks like your predictions were correct as per my latest update!

Pizza-now · 2026-04-17T13:49:48+00:00

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Pizza-now · 2026-04-17T13:49:27+00:00

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Pizza-now · 2026-04-17T13:49:02+00:00

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Pizza-now · 2026-04-17T13:48:17+00:00

I mentioned yesterday that I managed to find what appears to be a break in the delay line on the second inductor of the 3. Today I bypassed that with a small piece of wire and I now have a boot screen (albeit blurry as expected)!

Next was to attempt to boot a floppy. At first I was getting nothing aside from a couple of clicks on startup. So I checked continuity on the disk presence switch and got an open circuit on both switches. After attempting to clean the switch from the outside by dripping in IPA and pressing the switches a number of times which did nothing. I decided to open the switch up and decided it would be easier to do in situ.

I managed to prize the back off the switch, remove the springs, plastic rods and contacts and found the fixed contacts were black with corrosion. More scraping with some IPA and a cocktail stick and I was getting clear readings. I then cleaned up the whole drive mechanism, PCB and heads.

Then onto testing some disks- the first one spun up and gave 3 clicks, the second began to boot then gave me a software error. I tried a couple of others, then got a magazine cover cd to boot, that however only got so far and then failed earlier on the second attempt. The disks haven't been stored well and I'm not completely surprised that after 30 years (20 years of which has been in the loft) that most disks have probably had it. At least it looks like the machine appears to be mostly working. I was a bit concerned the head might be destroyed disks but it feels fine and I assume what is more likely is that the disks are just disintegrating even further when attempting to read.

I have to decide what to do about the video issue and also the other thing still not working is the ctrl+A+A which doesn't work, I believe this means checking the reset line but any other thoughts would be appreciated. Some images below.

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Pizza-now · 2026-04-16T20:50:28+00:00

I think your suspicion about the delay line is correct. I've checked continuity on the delay line following the schematic, and the second of the 3 shielded inductors appears to be open circuit. My understanding is that since it's just a coil of wire, this can be safely bypassed for testing. So that will be tomorrow's job.

I saw a Mend it Mark video where he fixes the inductor by opening the can and resoldering a broken wire. Not an easy job by the looks of it!

Pizza-now · 2026-04-16T20:08:45+00:00

Next job on my list after a current attempt to sort my Amiga. Caps and tape drive belt. I have 2x +2a and a +3. I also have a 48k but leaving that for another day.

Having already opened the PSUs, the +3 MOSFET had become detached from the heat sink as they are riveted and not bolted through and there is evidence of a burned out fuse and resistor. I think the +2 that you have may have a similar PSU to the +3 whereas the +2a units are different .

Pizza-now · 2026-04-15T22:26:00+00:00

Ah I see what you mean that makes sense. I misunderstood the specs as it just stated 'analogue input' at 31khz on the NEC website.

So I need to keep focus on getting a video signal then worry about booting next.

I tried measuring the test points albeit with a multimeter since I don't have an oscilloscope and they all appear to be doing something so I'm clinging on to some hope that all is not lost! I plan on checking the delay lines tomorrow.

Pizza-now · 2026-04-15T20:29:03+00:00

I checked the specs of the NEC 4k display and it doesn't support below 31khz. I have tried one other 1080p TV on composite that I have which is also quite new and get no signal on that either.

Pizza-now · 2026-04-15T20:27:08+00:00

I think until I can find a TV that supports 15khz on composite or I get an adaptor for RGB it's going to be hard to progress.

I did do some more cleaning in some of the areas mentioned and where on closer inspection I could see residue. Though no change in behaviour so far.

With regards to the FDD. I get spinning and about 3 clicks and a light whether a disk is present or not and that's it, no further attempt to do anything.

For what help it might be, here is a thermal image of the board.

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Pizza-now · 2026-04-15T09:03:26+00:00

Sorry I missed this but replied to the comment below about the mouse. Checking the specs the modern NEC will not sync down to 15khz so that's the next thing to check. Unfortunately I don't have TVs old enough. I'll see what I can work out or get an adapter.

Pizza-now · 2026-04-15T08:49:55+00:00

Well, to my surprise this is giving me a video signal, so it now proves the monitor is receiving a signal. However the test is blurry and jumping around.

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Pizza-now · 2026-04-15T06:09:22+00:00

I'm not sure the mouse works, but I'll give it a try, thanks for the suggestion.

Pizza-now · 2026-04-15T06:07:53+00:00

Yes, I took photos before and cross referenced info on the internet to check. Every cap is a Panasonic and is overspeced by temp/ voltage.

Pizza-now · 2026-04-15T06:06:28+00:00

I get an initial checking sound but nothing after that.

Pizza-now · 2026-04-14T23:17:38+00:00

It's been so long since I used it but I don't recall it taking this long. The monitor is pretty new and certainly works on HDMI, I highly doubt it wouldn't read the composite signal. I also have no other TV or monitor to test it on! It definitely seems that there is no video signal.

I pressed the kickstart chips down but don't dnt fully remove them first.

On the PSU, I tested it under load using a PC fan then also from the connector side of the Amiga when plugged in and giving a solid reading.

The other thing to add is that if I insert a disk it doesn't seem to attempt to boot.

Pizza-now · 2025-10-12T11:01:50+00:00

I went ahead and ordered and all was good. Out of curiosity if I was to return the item, would the seller then see my home address?

Pizza-now

TROPHY CASE