spectrum +3 "all-RAM page test failed"

[jgh73]

Hello,

I just joined the forum. I'm from Madrid, Spain. Maybe my english is not very good, so my apologies in advance..

A few weeks ago I have rescued a +3 from my basement that I bought second hand a couple of decades ago (and at that moment I barely checked it). I also owned a +2A but this is faulty (ULA failure)
I didn't have any disk with games (just a couple of blank disk a friend gave me from his Amstrad CPC) so I tried to load games from audio. I was able lo load some of them. Then a bought a DivMMC and there was a lot of games that don't load in the +3 most of them 128k games, but also 48k (like 1943, or bomb jack) I started to suspect of a hardware problem

Then I proceed to interchange the memories with the faulty +2A and the start screen also appeared but the problem with the loading of certain games persisted.

Then I posted this issue on a spanish spectrum forum, and someone told me about the auto test included in the ROM (holding BREAK while reset, and then pushing QAZPLM keys) The RAM test passed, but at the summary of the test appeared the message "all-RAM page test failed"

I suppose this RAM page test issue is related with the problem with the games loading, and i suppose that is a hardware problem, but I don't know how to continue with the diagnosis. So I post this here just in case someone can give me some advise.

Thank you!

[Alessandro]

Hola jgh73,

The original Elite release of Bomb Jack won't load on a +2A/+3. You will need to download the MCM re-release, which is compatible with them (more information here).

I also own a +3, and two +2As (+2Bs more precisely since they mount a V4.1 ROM), and a DivMMC EnJoy. I did not find any issues loading 1943 through the interface on these machines, therefore I am afraid that your problem could be related to the RAM fault you mention.

If the computer lets you proceed with the in-built test even after the "RAM page test failed" message, you should pass through these tests: GI sound, ULA (press SS+A), keyboard, ULA sound, joystick (you can pass it even without a Sinclair joystick attached, just press the keys from 1 to 0), cassette output, screen switching, printer (will fail if you don't have a suitable printer connected, but as you can guess, it's not really important these days), disk, tape.

Maybe other folks here could also help you by telling you how to check the voltage of some components on the computer's motherboard - unfortunately I can't because this is definitely not my cup of tea

[jgh73]

Thank you for your reply Alessandro!

Hola jgh73,

The original Elite release of Bomb Jack won't load on a +2A/+3. You will need to download the MCM re-release, which is compatible with them (more information here).

Yes I tried this versión and the +3 also crash... in all cases a get to the main menu of the game, I even can choose controls and the first screen appears, but then frezees

I also own a +3, and two +2As (+2Bs more precisely since they mount a V4.1 ROM), and a DivMMC EnJoy. I did not find any issues loading 1943 through the interface on these machines, therefore I am afraid that your problem could be related to the RAM fault you mention.

In the case of 1943 the music and the first game screen appears but with no options, and qhen i press any key it crashes.. so, yes, it seems that there is a hardware problem..

If the computer lets you proceed with the in-built test even after the "RAM page test failed" message, you should pass through these tests: GI sound, ULA (press SS+A), keyboard, ULA sound, joystick (you can pass it even without a Sinclair joystick attached, just press the keys from 1 to 0), cassette output, screen switching, printer (will fail if you don't have a suitable printer connected, but as you can guess, it's not really important these days), disk, tape.

Yes, I can proceed with the full in-built test. Actually the message "all-RAM page test failed" appears (among others like "printer test failed") in the summary at the end of the test

Maybe other folks here could also help you by telling you how to check the voltage of some components on the computer's motherboard - unfortunately I can't because this is definitely not my cup of tea

Yes, I would need some clue on how to make some aditional test. For the moment I have checked by changing the 4 rams, the ROMS and the CPU (from my faulty +2A) and the result is the same...

Thank you anyway!

[1024MAK]

If it fails with a full set of known good DRAM chips fitted, then either there is damage to one (or more) of the PCB tracks (traces), either the track itself or a broken/missing plated through hole. Or there is a problem with the circuitry that performs the bank switching.

So as the next step, with the machine disconnected from its PSU, using a multimeter on the continuity range or 200 ohm resistance range, test the connections between the DRAM chip pins and the gate array chip.

So for the main RAM, that is DRAM chips IC5 and IC6, Test A6 (pin 6) and A7 (pin 10) on each chip between the DRAM chip and the gate array (IC1) MA6 (pin 18) and MA7 (pin 19) respectively.

Then do the same for DRAM chips IC3 and IC4, Test A6 (pin 6) and A7 (pin 10) on each chip between the DRAM chip and the gate array (IC1) VA6 (pin 63) and VA7 (pin 62) respectively.

See the schematic diagram over on zxnet.co.uk

The above assumes that the machine will work as a 48K machine. If will only work as a 16K machine, then test all of the connections for IC5 and IC6.

If these connectors all check out okay, and there are no short circuit diodes D12, D13, D19 to D22, then the problem could be the gate array chip, this contains the bank switching circuitry. Alas there are no known spares of these.

Mark

[Mollymorgen]

Nice information.