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Amiga cdtv 1000 not working

Just got back from my business trip late last night and just finished installing a new porch light before the forecast storm arrives!

Those readings look good to me!

Excellent...

So, what I need you to do now is to leave the circuit as it is (with the temporary resistor in place of T2 in the collector of Q8).

Whilst measuring the dc voltage across the temporary resistor, what I would like you to do is to connect a short piece of wire from 0V/GND to the base of Q7.

With the temporary shorting link not present, both transistors Q7 and Q8 will be conducting and you should find a high voltage across the temporary resistor.

With the temporary shorting link present, both transistors Q7 and Q8 should be non conducting and you should find a low voltage across the temporary resistor.

Dave
 
daver2 said:
Just got back from my business trip late last night and just finished installing a new porch light before the forecast storm arrives!

Those readings look good to me!

Excellent...

So, what I need you to do now is to leave the circuit as it is (with the temporary resistor in place of T2 in the collector of Q8).

Whilst measuring the dc voltage across the temporary resistor, what I would like you to do is to connect a short piece of wire from 0V/GND to the base of Q7.

With the temporary shorting link not present, both transistors Q7 and Q8 will be conducting and you should find a high voltage across the temporary resistor.

With the temporary shorting link present, both transistors Q7 and Q8 should be non conducting and you should find a low voltage across the temporary resistor.

Dave
Click to expand...


Welcome back Daver!
Ok i soldered a little wire from gnd to Q7 base and in this way i have 0v across resistor....
 
Excellent. So we now know that Q7, Q8 and the surrounding circuitry is OK.

Remove the temporary piece of wire. Do you have a pushbutton or switch you could replace the shorting wire with?

Can you also remove the temporary resistor and solder Q8 back into the circuit please.

I will also need you to remove diode D5 as well (or disconnect one side of it from the circuit at least).

When you have done that, we can proceed with the next test - testing to see if transformer T1 is alive!

Dave
 
Ok thanks!
I removed wire and i inserted a switch.
I soldered Q8 on board.
I removed one side of D5 from board.
 
Excellent.

So, what I would like you to do now is to set your multimeter to dc Volts (on a low scale). Start off with something like 5 Volts or so full scale and decrease it to 1 Volt full scale (or even lower) if you fail to see a reading when you perform the test below.

Measure the voltage from 0V/GND to the junction of D5/R72.

Whilst measuring the voltage, turn the switch you installed alternatively ON and OFF.

What you are looking for is a ‘pulse’ generated in the feedback winding of transformer T1 when you change the state of the switch. This will be indicated by a pulse of voltage on your multimeter. Of course, an analogue meter is going to be best for this test...

What you might find helpful is to solder temporary flying leads onto 0V and the junction of D5/R72 and attach the two flying leads to the probes of the multimeter to leave your hands free. Of course, your multimeter may have clips to accomplish this without the flying leads.

Does this make sense to you?

Dave
 
1. Are you using an analogue meter or a digital meter?

2. You do remember you are looking for a pulse as opposed to a voltage level when you make and break the Switch?

If still nothing read, can you swap your multimeter for your oscilloscope (1 Volt/division).

Dave
 
daver2 said:
1. Are you using an analogue meter or a digital meter?

2. You do remember you are looking for a pulse as opposed to a voltage level when you make and break the Switch?

If still nothing read, can you swap your multimeter for your oscilloscope (1 Volt/division).

Dave
Click to expand...

Im using a digital multimeter....ok now i try with a scope...
 
Ok,

With the power OFF, can you measure the resistance (with your multimeter) between transformer T1 pins 2 and 3 and between transformer T1 pins 1 and 9 please.

Dave
 
daver2 said:
Ok,

With the power OFF, can you measure the resistance (with your multimeter) between transformer T1 pins 2 and 3 and between transformer T1 pins 1 and 9 please.

Dave
Click to expand...

T1 resistance:
Pin 2 to pin 3=0.005 ohm
Pin 1 to pin 9=05.5 ohm
 
Thanks,

I need to think a bit...

I am trying to work out whether you have a short-circuited T1 primary winding or the resistance is so low as to not read very well (i.e. it appears as a short circuit on your multimeter).

The secondary (feedback winding) looks Ok.

I just need to workout a suitable test for you to differentiate the two cases!

Dave
 
OK, first thing:

Can you measure the dc voltage from Q8 base to emitter when your temporary switch is both OPEN and CLOSED and post the results back please.

Switch OPEN. Q8 b-e voltage = ?
Switch CLOSED. Q8 b-e voltage = ?

I would then like to look at how you have configured your oscilloscope.

Dave
 
daver2 said:
OK, first thing:

Can you measure the dc voltage from Q8 base to emitter when your temporary switch is both OPEN and CLOSED and post the results back please.

Switch OPEN. Q8 b-e voltage = ?
Switch CLOSED. Q8 b-e voltage = ?

I would then like to look at how you have configured your oscilloscope.

Dave
Click to expand...

Switch OPEN. Q8 b-e voltage = 0V
Switch CLOSED. Q8 b-e voltage = 0,94V
 
I suspect the switch is the other way around - but the principle is that Q8 b-e voltage is changing when you operate the switch. That was what I was expecting to see.

Do you have a 9V battery (or something close) and a 100 Ohm resistor (or something close) to hand?

Dave
 
Yes maybe the switch is in the other way!
Yes i have 9v battery and 100ohm resistor!
 
Excellent.

So, what we are now going to do is to test the transformer by injecting a 'pulse' of current into one of the windings and monitoring the output pulse on another winding.

To do this you are going to connect the 100 Ohm resistor in series with the 9 Volt battery (to limit the current flow to a maximum of 9/100 = 90 mA) and use this as a 'stimulus'. You are going to use your oscilloscope to measure any resultant pulse in the second winding.

This test is performed with the power switched OFF to the Amiga CDTV-1000.

Connect your oscilloscope up to T1 pins 1 and 9. Signal to T1 pin 9 and screen to T1 pin 1. Set the oscilloscope for something like 100 mV/division and a slow timebase. Put the Y-level (with no signal) in the middle of the screen. All we are looking for is a 'glitch' appearing on the oscilloscope whenever you connect and disconnect the battery/resistor to the other winding.

Connect the battery/resistor series combination to T1 pins 6 and 8 (with the display NOT connected). It doesn't matter which way around the leads go.

Observe any glitches on the oscilloscope when connecting and disconnecting the battery/resistor.

If you don't see anything at all. Put the oscilloscope on T1 pins 6 and 8 and the battery/resistor on T1 pins 1 and 9 and see what happens when you connect and disconnect the battery/resistor.

Keep your fingers away from touching any wires when you do this - just in case things work! You may get a little electric shock if you touch the parts!!!

If you see some glitches on the scope, then we can look at the primary side next.

If you don't see any glitches, can you post a photograph of your oscilloscope screen please.

Dave
 
daver2 said:
Excellent.

So, what we are now going to do is to test the transformer by injecting a 'pulse' of current into one of the windings and monitoring the output pulse on another winding.

To do this you are going to connect the 100 Ohm resistor in series with the 9 Volt battery (to limit the current flow to a maximum of 9/100 = 90 mA) and use this as a 'stimulus'. You are going to use your oscilloscope to measure any resultant pulse in the second winding.

This test is performed with the power switched OFF to the Amiga CDTV-1000.

Connect your oscilloscope up to T1 pins 1 and 9. Signal to T1 pin 9 and screen to T1 pin 1. Set the oscilloscope for something like 100 mV/division and a slow timebase. Put the Y-level (with no signal) in the middle of the screen. All we are looking for is a 'glitch' appearing on the oscilloscope whenever you connect and disconnect the battery/resistor to the other winding.

Connect the battery/resistor series combination to T1 pins 6 and 8 (with the display NOT connected). It doesn't matter which way around the leads go.

Observe any glitches on the oscilloscope when connecting and disconnecting the battery/resistor.

If you don't see anything at all. Put the oscilloscope on T1 pins 6 and 8 and the battery/resistor on T1 pins 1 and 9 and see what happens when you connect and disconnect the battery/resistor.

Keep your fingers away from touching any wires when you do this - just in case things work! You may get a little electric shock if you touch the parts!!!

If you see some glitches on the scope, then we can look at the primary side next.

If you don't see any glitches, can you post a photograph of your oscilloscope screen please.

Dave
Click to expand...


Very difficult job :(
It's correct in this way?
Schermata 2020-02-15 alle 18.27.55.png
 
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