Spectrum 128K +2 Fault Conformation?

[Reminis]

Hi all, just joined. I have an issue when I plug in the cassette lead to the main board it kills the output and have found what looks like a burnt out resistor but will need info on it and possible reasons why (pics below) and thanks in advance...

More detail: My dad just found the speccy in his loft and dropped it round. It was from new during the war, always worked and when it was packed away it worked.
I unpacked it and plugged it in, power light came on and tuned to TV showing the good old choice screen (that was a flash back from the past).
I was so excited to get loading my old fav's and within about 30 to 40 secs I could smell something like hot electrics from the ext port, so I quickly unplugged it and cleaned it out finding a few little bugs and fluff/dust etc near the heat sink. So I thought that's all it was, just cooking some bugs for dinner.

Unfortunately not, when I plugged it in again it still smelt. I googled it and some posts said that after 37yrs the plastics can re-aquire form and that could be it. I ran it again (case opened so I could see whats going on) and saw no smoke.
However, this time the red power indicator didn't come on and nothing loaded.
So I just ran the main board without the cassette or ribbons plugged in and it loaded properly again. So I tried one at a time and found it fails when I plug in the cassette plug.
Looking at the board that the cassette plug goes to (TCI-AI2H 94HB)) I found what looks like a burnt out resistor (location L30I), it's kinda dark brown in the middle.

So, does anyone know exatcly what type of resistor I need and where to get it from? and even if it is burnt out, should it look like that?
Also, If I just replace the resistor will that also burn out, could the reason it burnt out be something else or is it common?

I'm kind of a noob to this so I'm not as up to date on it as you masters!

Thanks in advance and sorry for the long post.

[Guesser]

It's not a resistor, but an inductor. The value according to the schematic is 82μH.

For it to have burnt up something else in the circuit is presumably shorted out.
Do you mean that when you plug the tape board in it kills the machine? That would be consistent with it having a short on the 5 volt rail.

[Reminis]

It's not a resistor, but an inductor. The value according to the schematic is 82μH.

For it to have burnt up something else in the circuit is presumably shorted out.
Do you mean that when you plug the tape board in it kills the machine? That would be consistent with it having a short on the 5 volt rail.

Thanks for the reply Guesser, that goes to show how little I know
Does it look burnt out to you in the picture?
And yes, when I plug the tabe board into the main board it kills the machine, remove it and it works again.
Where do I find the 5 volt rail so as I can look more carefully at it?

Many thanks

[Guesser]

You can find the schematic for the tape board in the +2 service manual https://spectrumforeveryone.com/wp-cont ... Manual.pdf

The short would be something after the inductor, possibly C323 if it's not a short in the motor or switch wiring.

[1024MAK]

Nearly all of the main board runs off the +5V supply. This comes from the voltage regulator (attached to the heatsink).
On the main board, this +5V rail is tapped off to feed the connector that goes to the tape deck board.

As Guesser says, whatever has gone short circuit will be after the now slightly cooked inductor. This appears to still be conducing electricity, but although it’s not ‘burnt out’, the overheating may have changed its value. So normally it’s recommended to renew it. But not until the source of the short circuit has been found.

The most likely cause is either a piece of metal (foreign object) or one of these parts:
Ceramic disc capacitor C323 0.022µF (22nF) (marked 223Z)
Electrolytic capacitor C322 470µF 10V or 16V
The motor or the wiring to it, or to the leaf switch (operated by the play key)

Neither ceramic disc capacitors or electrolytic capacitors normally fail short circuit unless there is visible signs of damage.

Mark

[Reminis]

Lot's of very helpfull information from the above posts, looks like I've got a busy day tomorrow
Thanks everyone!

[Reminis]

Result, it was the Electrolytic capacitor C322 that was causing the black screen once cassette plugged in. Thanks guys. On another note, how the hell do I get sound from it? What cables?

[1024MAK]

I presume you mean sound from the computer?

Use a 3.5mm mono jack plug and connect to an audio in on a amplifier or other device. Most amplifiers these days are stereo, hence you may not get away with a stereo to stereo lead. I forget which version socket is used on the +2 Grey.

Later on, if you want, I’ll have a look at mine.

Mark

[Reminis]

I presume you mean sound from the computer?

Use a 3.5mm mono jack plug and connect to an audio in on a amplifier or other device. Most amplifiers these days are stereo, hence you may not get away with a stereo to stereo lead. I forget which version socket is used on the +2 Grey.

Later on, if you want, I’ll have a look at mine.

Mark

Thanks Mark, yes... I have tried a old school mono cable but nothing. Guessing my TV is stereo only.
Any work arounds?

[1024MAK]

So, just to be clear, generally speaking, 3.5mm mono plugs are not compatible with stereo sockets. And generally speaking, 3.5mm stereo plugs are not compatible with mono sockets.

And yes, the 3.5mm socket on a +2 grey is a mono type (unlike on the +2A/+2B/+3 which is different).

So you really need a 3.5mm mono plug to a 3.5mm stereo plug (if your TV uses a 3.5mm stereo socket). These are, not very common. So you may either have to make your own up, or use various cables and adaptors. It’s fine to feed the mono audio from the Speccy to both the left and right channels on your amplifier/TV.

Do you have a 3.5mm stereo jack plug to 3.5mm stereo jack plug cable? That may work. Even if you only get sound from one audio channel on the TV.

There is however something similar: “3.5mm STEREO Jack Plug to 2 x MONO Jack Plugs SPLITTER Converter Cable Lead 1m” on eBay that I use for various purposes. But obviously if you used this lead, you would only get sound from one audio channel on the TV.

Having said all that, sometimes you can get a temporary connection by not fully inserting an incompatible 3.5mm jack into the socket. But you need the Speccy to be playing a sound continuously so you know when you get the plug contacts to the ‘sweet spot’ position

Mark

[Reminis]

Thanks again Mark. I did fashion my own old school mono to mono lead (3.5mm) but no joy. I did try inserting to different depths but no luck. So maybe you say try a mono to stereo connection? I don't know how I would do that tbh. I'm reluctant to spend £15 on the rgb connector.

[Reminis]

It's not a resistor, but an inductor. The value according to the schematic is 82μH.

For it to have burnt up something else in the circuit is presumably shorted out.
Do you mean that when you plug the tape board in it kills the machine? That would be consistent with it having a short on the 5 volt rail.

The fault was capacitor C322. L301 is listed in the manual/schematic as a inductor, but it is not, please see my original pics (1st). Maybe they changed something between models but L301 is definitely not an inductor. I've found the inductor related (defo not the part in my pics) and it's a resistor. Question is which one? Now I've fixed the reason for the resistor burning I'd like to replace it but it's too burnt to get the colour codes and manual is incorrect. Any ideas?

[1024MAK]

L301 may look like a resistor, but that does not mean that it is a resistor.

Here’s a possible replacement (link).

Mark