question marks everywhere

[jojo]

who can tell me what this is ;

[1024MAK]

A wild guess: something to help with either loading or saving maybe???…

Mark

[XavSnap]

Yes, seem to be an audio amplifier based on a simple darlington feature (transistors), drive by a variable resistor and electronics filters.
... Or unused something to do nothing else...



In my opinion, it's a crappy something to trash... DON'T USE IT !!!

[Moggy]

Agree with Mark re load/save and it does look like a small audio amp though doubt it's a Darlington pair configuration as the transistors look mismatched and also such a pair would be overkill for this. It looks more like a before and after amp in the sense that one transistor is there as an impedance matcher set at unity gain with the second transistor bringing the signal back up to speed by amplifying the signal level losses from the passive filter network.

What part of the board was this connected to?

[jojo]

thanks all for helping me out.

sorry , image with original situation has been blown into digital blue.

white cable was connected to the lower speaker connection ( issue 2 pcb )
yellow cable was connected to input of rf modulator
there is a switch to activate it

i have removed it and re-connected all back to original .

unfortunately the problem remains the same .

only very vague vertical gray lines in a gray backgroend.

so i need to verify the internal switcher to get all voltages back .

[1024MAK]

thanks all for helping me out.

sorry , image with original situation has been blown into digital blue.

white cable was connected to the lower speaker connection ( issue 2 pcb )
yellow cable was connected to input of rf modulator
there is a switch to activate it

i have removed it and re-connected all back to original .

unfortunately the problem remains the same .

only very vague vertical gray lines in a gray backgroend.

so i need to verify the internal switcher to get all voltages back .

Based on the above, it could be a device (audio “modulator”) to add sound to the RF/UHF TV signal. Unless that’s something you want, it’s best to disconnect it.

Mark

[Moggy]

I suppose it works in the same signal mixing manner as the Currah Microspeech which if memory serves always produced wavy lines on the screen which no amount of turning the little micro adjustment screw on the unit would get rid of.

[jojo]

Thanks for answering me ,

now the strange connection to the video-line makes sense .

so now i understand the reason for the switch .

is there any info available on this "system" as the pc has been nicely made .

[XavSnap]

Hi,

Jojo, if you plan to keep this audio mixer, you had to change the input and the output audio wires.

In fact, the audio signal is drive to an unshielded electric wire, and this wire is an "antenna" and collect all electromagnetics noises.

The high frequency noises from the Z80 or all electronics process are added to the sound signal and generate the high frequency screen waves.

Change the both sound wires by shielded one, and connect the shield wire to the ground.

In fact, all the circuitry had to be enclosed in a metal box, to protect it from electromagnetics garbages.

[Moggy]

Hi,

Jojo, if you plan to keep this audio mixer, you had to change the input and the output audio wires.

In fact, the audio signal is drive to an unshielded electric wire, and this wire is an "antenna" and collect all electromagnetics noises.

The high frequency noises from the Z80 or all electronics process are added to the sound signal and generate the high frequency screen waves.

Change the both sound wires by shielded one, and connect the shield wire to the ground.

In fact, all the circuitry had to be enclosed in a metal box, to protect it from electromagnetics garbages.

The wavy lines are a natural feature of sideband interference when the audio is mixed with the UHF signal not something picked up from the board.
The simple audio transistors seen here usually roll off or fail to amplify anything over 20khz and looking at the components used I detect a simple Zobel network has been employed should that happen and that plus using the wires as a twisted pair (used in an audio sense) will suffice I would have thought also the out put of a power amp doesn't usually require shielding as its signal is stronger than any interference especially the minute levels found here.