Spectrum 128 +2 grey loading issue

acsi
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Spectrum 128 +2 grey loading issue

Post by acsi »

Hi

My Spectrum +2 Grey has developed an issue where it will appear to load fine (displaying the loading screen etc) but when it gets to the end of the program it will reset and display (c) Amstrad and lockup.

edit: It runs programs fine from the Divide Plus

I've left it on a soak test with a diagnostic rom and everything seems to work fine.

My initial thought is Capacitors but thought I'd ask if anyone else has had the same issue before?

Thanks
acsi
Posts: 47
Joined: Tue Apr 23, 2013 12:03 pm
Location: New Zealand

Re: Spectrum 128 +2 grey loading issue

Post by acsi »

OK Some progress as I managed to get it to load "Reaper".
Trying "Splatter" again it either doesn't pick up the header (No program displayed) or gives a tape loading error.

Now I'm thinking the Azimuth needs adjusting... haven't done that it years (Probably 1984 or 85 with a ZX81).
acsi
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Joined: Tue Apr 23, 2013 12:03 pm
Location: New Zealand

Re: Spectrum 128 +2 grey loading issue

Post by acsi »

Maybe not. By adjusting the azimuth I managed to get it to get it to successfully load "Jetpac" once as well as "Splatter". However it will not load again and goes back to "Tape Loading error" or a reset back to "(c) Amstrad".

Whilst in the process of doing this I also noticed that the AY is extremely quiet. Testing it with a test ROM I can just make out a bit of tone but the noise seems to work ok.

Back to suspecting the Caps. Although I may replace the AY while I'm at it (Or at least order one along with the capacitor kit).
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1024MAK
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Re: Spectrum 128 +2 grey loading issue

Post by 1024MAK »

Three things:

Do you have a multimeter?

Have you cleaned to tape deck head and the rollers and rest of the tape path.

Have you tested the sound just using a test ROM, with a game or using BASIC, and how are you listening to the sound?

Mark
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acsi
Posts: 47
Joined: Tue Apr 23, 2013 12:03 pm
Location: New Zealand

Re: Spectrum 128 +2 grey loading issue

Post by acsi »

Do you have a multimeter?
Yes
Have you cleaned to tape deck head and the rollers and rest of the tape path.
Yes and replaced the belts which were quite loose
Have you tested the sound just using a test ROM, with a game or using BASIC, and how are you listening to the sound?
Test rom and I first noticed it after loading Rick Dangerous 2 from my Divide. Beeper sound seems to be fine as I get the beeps during the beginning of loading Jetpac.

To hear the AY sound I have to turn the monitor volume up to max. Interestingly trying it again this morning it is louder when the machine is cold.

Looking at the modifications page on Retroleum as I'm now using the RGB port and Sound socket I'll check the value of R115. (Was using RF before now)
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1024MAK
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Re: Spectrum 128 +2 grey loading issue

Post by 1024MAK »

If you have a multimeter, then I presume you have checked all the supply rails. Nearly all the circuitry runs off the main +5V supply from the 78S05 voltage regulator, including all the audio and sound circuitry. This should be between +4.75V and +5.25V although most regulators normally manage to be much closer to +5V

The sound from the beeper (generated by the ULA) and the GI AY-3-8921A sound chip have always had different sound levels. The volume of the beeper has no direct control. While the AY has a register to control the attenuation (volume) of each of the sound channels.

Apart from for the supply rail, there are no electrolytic capacitors involved in the sound circuitry for either the bleeper (ULA) or the AY sound chip if using either the audio/tape/sound out socket or via the Monitor/RGB socket.

If using the TV/RF/UHF, then there are three 1uF electrolytic capacitors, but these have a very easy life and are unlikely to have failed. The 5V supply to the audio modulator chip for the TV/RF/UHF output does have a 220uF electrolytic capacitor.

With regards to the tape deck, you have done all the obvious things.
Are all the machine screws on it tight? IIRC one acts as a 0V/GND connection, hence if loose can cause strange and intermittent symptoms. It’s also worthwhile testing the switch that controls the motor. Dirty contacts will not help.

On the main PCB, (excluding the electrolytic capacitors for the supply rails), there are no electrolytic capacitors in the circuitry for the incoming audio from the tape deck.

There are some electrolytic capacitors on the tape deck PCB however.

Do you have a battery powered amplifier?

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.
acsi
Posts: 47
Joined: Tue Apr 23, 2013 12:03 pm
Location: New Zealand

Re: Spectrum 128 +2 grey loading issue

Post by acsi »

Voltages test as. (before and after recap)

PSU shows 11.2v unloaded and 9.5v loaded

5v - 4.9v
12v - 11.1v
-5v - -5.1v

While I was in there with the soldering iron I reflowed the joints between the motherboard and the tape pub just to rule out a dry joint.

However loading still fails. Right at the end of the recording it resets back to the (c) 1982 Amstrad message?

Tape motor on play is showing 4.6v which seems a bit low?

Anyway I did notice when testing the ULA with retroleum's diagrom it brings up a message saying "ERROR: EAR stuck high!"?
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1024MAK
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Re: Spectrum 128 +2 grey loading issue

Post by 1024MAK »

What’s the DC voltage on pins 34 and 35 of the ULA?

It’s common if there is a loading problem for the machine to “reset” and display the copyright message. Only some tape loading problems result with a tape loading error message.

This copyright message is coming from the (16K/48K) BASIC ROM. The machine is not really being reset, rather the processor is ending up doing the equivalent of a “NEW”.

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.
acsi
Posts: 47
Joined: Tue Apr 23, 2013 12:03 pm
Location: New Zealand

Re: Spectrum 128 +2 grey loading issue

Post by acsi »

What’s the DC voltage on pins 34 and 35 of the ULA?
Pin 34 = 1.5v
Pin 35 = 0.5v
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1024MAK
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Re: Spectrum 128 +2 grey loading issue

Post by 1024MAK »

Are those results with the cassette deck connected?

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.
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