ZX Spectrums problems : diagnostic software ?

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1024MAK
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Re: ZX Spectrums problems : diagnostic software ?

Post by 1024MAK »

There are plenty of other places where you can connect the negative probe of the multimeter, such as the modulator case, the appropriate DC input connector pin, the 0V fingers on the edge connector, various capacitor legs, etc...

Mark
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dizzy33
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Re: ZX Spectrums problems : diagnostic software ?

Post by dizzy33 »

I just received my Retroleum Smartcard V2. When I ran the diag test from its ROM, the diag test returned some low RAM failing.
I have replaced ALL my low RAM (8 chips). As a reminder, I also replaced my Z80 as the M1 line was dead, the 7805 with a TRACO, replaced both TR4 and TR5, and did a full RECAP.
So now, my Smartcard V2 does not report any RAM failing anymore, but my Speccy still behave like if there was a RAM issue : less games a failing, but there are still many which fail to load. Plus, when the Speccy is getting more hot, I can see a few bugs on the left of the screen (some "." are displayed).

I also tried to run the ZX-Diagnostics, but not from ROM, and then it says some low RAM are failing, but never the same ... Sometimes it says bits 3 and 7 are failing, sometimes it says bits 0,1,2,3,4,5,6,7 (all !). But as it runs from RAM, I don't think I can believe what it says.

So I don't think this is really a RAM problem as my Smartcard V2 does not find any failing RAM anymore (even if I still have a doubt on the RAM sockets I receive which are of a very bad quality : if you remove the RAM chip from the socket, then some socket contacts just leave the socket ! I already had to replace 3 of them which were dead !!)

So I am totally lost now ...

Can someone help me ?
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1024MAK
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Re: ZX Spectrums problems : diagnostic software ?

Post by 1024MAK »

I would still like you to do the voltage tests that I asked you to do earlier:
1024MAK wrote: Sun Feb 02, 2020 10:45 pm What do you get on the following power rails:
  • +9V (nominal) input?
  • +12V ?
  • -5V ?
If these power rails are outside the normal range, the 4116 DRAM chips will malfunction.
At the same time, can you please test the +5V rail.

You also say that you are having problems with the DIP/DIL sockets that you got. The cheap type are only designed for a small number of insertions and removals. If ANY pin/socket contact is not making a good connection, this will eventually cause strange symptoms. Intermittent contact problems are very hard to track down.

Mark
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dizzy33
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Re: ZX Spectrums problems : diagnostic software ?

Post by dizzy33 »

1024MAK wrote: Mon Feb 17, 2020 11:34 am I would still like you to do the voltage tests that I asked you to do earlier:
1024MAK wrote: Sun Feb 02, 2020 10:45 pm What do you get on the following power rails:
  • +9V (nominal) input?
  • +12V ?
  • -5V ?
If these power rails are outside the normal range, the 4116 DRAM chips will malfunction.
At the same time, can you please test the +5V rail.

You also say that you are having problems with the DIP/DIL sockets that you got. The cheap type are only designed for a small number of insertions and removals. If ANY pin/socket contact is not making a good connection, this will eventually cause strange symptoms. Intermittent contact problems are very hard to track down.

Mark
Thanks a lot Mark, in fact I just ordered new sockets of another type (the one with the round holes, in french we say "tulipe" type, I do not know the english word for this. I hope it will correct the problem (the more I think about it, the more I'm pretty sure that my problem finally comes from my new sockets ...).
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1024MAK
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Re: ZX Spectrums problems : diagnostic software ?

Post by 1024MAK »

The type with the round holes, we usually call ‘turned pin’.

Mark
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dizzy33
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Re: ZX Spectrums problems : diagnostic software ?

Post by dizzy33 »

1024MAK wrote: Mon Feb 03, 2020 8:04 pm In circuit resistance tests can be misleading, as the results are affected by the type of multimeter used.

Before anything else, I strongly recommend you carry out these voltage tests. For all these tests, you need a digital multimeter switched to a 20V DC voltage range.

For the +9V and the +5V, the easiest place is to test on the 7805 voltage regulator chip (assuming it has not been changed to a DC/DC converter). This is the chip mounted on the large aluminium heatsink.

The left hand leg is the +9V (which is typically between 10.5V and 12V), the middle leg is 0V/GND, the right hand leg is the +5V output.

Use the metal tab of the 7805 voltage regulator chip (which is also connected to 0V/GND) for the negative (black) meter probe. The carefully use the positive (red) meter probe to measure the +9V and the +5V legs. Be careful not to slip and short out to the middle leg.

Next, the +12V and the -5V rails.

The easiest way to test is either on the edge-connector contacts, or on the pins of one of the 4116 DRAM chips.

Note that some diagrams in some Sinclair documentation (including some of the manuals) show a "-12V" supply pin as well. Ignore this, the name is supposed to be "~12V" (where the ~ is a wavy line) as this is a AC waveform, not a DC supply. The supply rails that you should test are however, labelled correctly.

Test all of them with respect to the 0V pin (-V/black meter lead connected to the 0V pin) or to the 7805 voltage regulator tab (as earlier).

Image
(This pin-out is one of a number in a thread that is linked to in my signature ;) )
A copy of the full data sheet is here

Pin 1 is VBB, which is -5V (-5.5V to -4V)
Pin 8 is VDD, which is +12V (+10.8V to +13.2V) (although lower than 11.5V normally indicates a problem).
Pin 9 is VCC, which is +5V (+4.75V to +5.25V) (the output from the 7805 regulator is normally very close to +5V)
Pin 14 is VSS, which is 0V (ground/GND)
(Voltage tolerances taken from here

Please post up your results.

Mark
I am sorry but even if your message is very detailed, I don't understand how to do the measurement (I am totally noob in electronic) :
I own a multimeter which I can put in "20v DC" as you request, but it's not clear to me how to do the tests you are requesting.
At first, I guess my Speccy should be powered on, right ? So I am very afraid of making a shortcircuit, that's why I am asking so much questions.

Then, as I don't have a 7805 regulator but a Traco regulator, should I put the negative probe of my multimeter on the modulator case ? (I did a composite mod, is this still working ?) are where else exactly ?

Is testing my new Traco regulator necessary as I just replaced it ?

To be sure I understood well the ram chip tests : I put the black probe on pin 14v, then alternatively the red probe to pin 1,8, and 9 ?

Sorry for these stupid questions, but again I am totally noob and very afraid of burning my Speccy ...
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1024MAK
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Re: ZX Spectrums problems : diagnostic software ?

Post by 1024MAK »

Would a video help?

Mark
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dizzy33
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Re: ZX Spectrums problems : diagnostic software ?

Post by dizzy33 »

Oh yes !!! Definitly ! I was just checking Youtube to see if some videos were there ...
But please, when you will make the video, remember that I don't have a 7805 regulator, but a TRACO regulator.
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1024MAK
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Re: ZX Spectrums problems : diagnostic software ?

Post by 1024MAK »

I’ll see if I can do a video at the weekend. And I will take into account your use of a modern DC/DC converter (TRACO).

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
dizzy33
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Joined: Mon Jan 13, 2020 3:24 pm

Re: ZX Spectrums problems : diagnostic software ?

Post by dizzy33 »

Thanks a million !
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