• Please review our updated Terms and Rules here

ZX Spectrum 48K Repair. I could really use some help from the other side of the pond repairing this...

Ah, right, I see there is an added level of complication in so far as it creates a unique fast loading format. Unfortunately I'm back at the point where I'm out of time to make progress with actual hardware and I am away for the weekend so I'll have to have a look at this next week.

In the meantime maybe you can go forward with your idea of trying a diagnostic EPROM because it is possible that the root cause of your trouble may be a still outstanding hardware problem.

Gary, can you suggest a known TAP to WAV converter for Windows (Most of my Windows machines which I use for this kind of thing are are XP).
 
Will do - I did already watch it with the sound down and subtitles on as it is late here, but maybe something was lost in translation. I'll have another go early next week.
 
OK, so I found a little bit of time to move a step further forwards.

-OTLA loaded on 11" Dell 1011 netbook (Windows XP). Audio output volume set to 90%
-Mono to mono 3.5mm jack lead plugged into 'Ear' on Spectrum. Stereo to Stereo jack lead plugged into headphones-out on Dell.
-Used short croc leads to join PC GND to Spectrum GND and one (only) of the Dell's stereo outputs to Ear-signal-In on the Spectrum.

Result: Working first time every time with the examples supplied with OTLA, for example Manic Miner, and the Psion Space Invaders knock-off (shown running below after being loaded with OTLA). It works equally well in speed loader mode or normal speed mode. I find the speed loader feature very impressive, what a great bit of software.

I didn't yet have time to transfer your TAP file onto the netbook and try that - I will do that later in the week. But at least I can say that in principle there should be no problem loading your Spectrum up with OTLA, it works for me.

One thing to bear in mind when you are loading from a 'device' like a computer or a smartphone, any sounds (like system sounds) which the device itself makes will be mixed in with the file being played out to the Spectrum and will disrupt the playback - for example if an email arrives and the system goes 'bong' to announce that, that sound (or any other system sound) will wreck the playback - so when you are trying to do something like this, you really need to have every other potential source of sound on the 'device' muted or turned off.
 

Attachments

  • Loaded_With_OTLA.jpg
    Loaded_With_OTLA.jpg
    1.6 MB · Views: 8
Last edited:
I've also just read back to the point where Verault got onto the subject of trying to load software and I have realised I see no specific mention of the use of the MIC and EAR sockets on the computer, and which should be used, when.

Just in case it is not clear, the audio-out from the tape player or other source should go to EAR, which is an input on the computer. Audio-out FROM the computer TO the recorder is from the MIC jack, in other words MIC on the computer is an OUTPUT. The labels on the computer's sockets indicate which sockets on the recorder / player they should be connected to.

It wouldn't be unreasonable to assume that phones-out on the player should go to the socket marked 'MIC' on the computer because any socket marked 'MIC' is normally an audio input... but in this case, it is not. The socket you should be playing the sound into is the EAR socket.

I wonder if that is the problem?
 
The video I referenced from mark fixes stuff which goes on about using OTLA makes it pretty clear to use only mono cables and connect to the EAR input. Also I mention that I do get the name of the program loading on screen. That would not be possible if I was using the wrong jack.. I dont think I would get flashing bars either.
 
Last edited:
Actually if you played it loud enough, really loud, it could work. Both sockets eventually go to the same ULA pin, the main difference is the values of the series resistors - there is a lot more attenuation between the ULA pin and the MIC socket than there is between the ULA pin and the EAR socket.

Point taken though, you are using the right socket. It seemed like a potential area for confusion with the sockets on the computer being labelled with what they go TO, rather than what they ARE, so I felt I'd better rule that out.

In that case I don't know what to suggest, other than programming a diagnostic EPROM as you had suggested. You already said that the diagnostic TAP was not the only one you were unable to load. Maybe there's some remaining underlying hardware problem, of which this inability to load is just the most obvious symptom. Sorry I haven't been able to help you more, other than by confirming that what you are doing should work.
 
No I understand we need to cover all the bases. But that is why I showed the video. I used it as a guideline on how to do what I am trying to achieve.
 
Did you make any progress on this? My TS1500 would load but not save. I finally tracked that down to a glass capacitor in the audio circuits, located adjacent to the rec/play jacks.

The scoped audio shows very definite waveforms that may help with troubleshooting. I don't own a scope but I've seen a magazine article about the ZX81/TS1000 showing examples.

I built this dongle that adds an old record level meter and an earphone monitor. That's been a big help with adjusting levels and listening for dropouts. I use it on both the TI99/4A and my Timex gear.

!LoadMeterDongle.jpg
 
I do have a few things to report. I am just waiting till I have some time. lets just say the reason tapes were not loading was far deeper than connections or cables. the board has bigger issues. Again will report more when I have time. I have not even come close to giving up on this.
 
I finally tracked that down to a glass capacitor

I would be interested to know which actual part that is. I can't think of any glass-like capacitors in the Spectrum, unless maybe you mean polystyrene types which have transparent bodies with silver foil visible inside.
 
To be honest, that was where I was going with this, as there are no polystyrene capacitors listed in the Spectrum parts list, only ceramics and electrolytics. But then I was wondering what the faulty part has been replaced with.

The diodes in question are supposed to be 1N4148s, I don't know about the Spectrum off hand but certainly the 1N4148 in my original MK14 tape interface has a tubular body with yellow, brown, yellow, grey bands on it. You can see what they did there. It wouldn't be unreasonable to mistake one of those for a capacitor at first glance.
 
Looking at the best image I can find, here is a crop from the tape in / tape out section of an issue 3 Spectrum PCB.

The diode is quite obvious, the small pinkish component running vertically away from the right hand end of the crystal with the black polarity band at the upper end. The two highly glazed yellow components are perhaps the ones which have been identified as glass-like?

tape_components.jpg
 
Sorry Guys. I wrote above-
Did you make any progress on this? My TS1500 would load but not save. I finally tracked that down to a glass capacitor in the audio circuits, located adjacent to the rec/play jacks.
I was referring to my Timex SInclair TS1500, not the Speccy. I didn't know nor check to see if the Spectrum was similar or not. Guess I should have or at least made it more clear I wasn't talking about a Spectrum. Glass or styrene I don't know, but C18 broke and shattered when removing it. It was the bad one. Here's a pic of the glass caps C18 and C10 in the TS1500.
TS1500.Motherboard.Top.jpg
 
Last edited:
Hi Ed, you made it perfectly clear that you were talking about a Timex. My mistake was assuming that the Spectrum and Timex versions were similar enough to compare. Thanks for showing the actual component which was the problem.
 
I was looking at various online photographs of the TS1500 and observed different types of capacitor in these locations. One of the types was clearly a ceramic disk capacitor (similar to a decoupling capacitor).

That got me thinking. On our Honeywell boards, all of the decoupling capacitors are little glass devices...

1657009125939.png
They really explode well when thy go pop!

Dave
 
Last edited:
There is another interesting failure mode for glass bodied components, it starts with them being inserted into the PCB with the leads not perfectly formed to go straight into the holes in the PCB, and in fact this is often deliberate so that the component is held in place by spring tension, ready to be soldered. So from that point on, the body of the component is under steady spring pressure applied to it by the tension in the bent leads.

As everyone will have read at some point, glass is not really a solid but a very slow moving liquid. After about 30-40 years, the constant pressure applied to the body by the leads makes the component crack in half. I have often traced faults to glass components, especially diodes, only to have them fall apart into two halves as soon as I desolder one end, no matter how carefully I do that.
 
Last edited:
I was looking at various online photographs of the TS1500 and observed different types of capacitor in these locations. One of the types was clearly a ceramic disk capacitor (similar to a decoupling capacitor).

That got me thinking. On our Honeywell boards, all of the decoupling capacitors are little glass devices...

View attachment 1243247
They really explode well when thy go pop!

Dave
I have come across some blown caps exactly the same as this one (103's) on a few machines. A Franklin Ace 1200 Keytronic keyboard PCB in fact. The ribbon cable for the KB was not keyed so when inserted backwards it fried the ROM, 3 TTL chips, and a few of those glass caps. I replaced them with standard disc ceramics and it worked fine. hey just take up a bit more height.
 
Back
Top