Geloso Electronic Voice Control 9095-A

[Lef de art]

Hello forum. I have buy this Electronic Voice Control 9095-A for my geloso g268 reel to reel.
it is a transistored accessory on which the microphone is connected.
Two cables from it are connected to the recorder.
One to the microphone input to carry sound and the other cable pauses the tape recorder when no sound is detected.
Its mechanism is quite simple.
I tried it as soon as I bought it but unfortunately it keeps the tape recorder paused as soon as I connect it and it doesn't go into record mode when it detects sound.
Unfortunately the situation did not change at all even when I changed all the capacitors, electrolytic and paper. I suspect that the fault is in transistors. Does anyone have any idea how I can replace them? Where I can find them. They don't have any inscription

[DMcMahon]

As shown on the schematic the transistors left to right are OC75, OC72 & OC80 respectively. These are all very old Germanium PNP bipolar transistors. If the trasistors themselves are not marked you can work out which one is which by checking the associated connected components as shown on the schematic.

You may well find online sellers selling these, of course they will be old, probably NOS so no gaurantee that they will be good. There are many alternatives listed online.

I would first measure the DC voltages at all 3 legs of each transistor noting which voltage is which connection, i.e. base, emitter or collector in case that gives any clues.

You could also carefully remove each transistor one at a time and test them. A transistor tester would give a more comprehensive test but a DMM with diode check facility would check for good forward and reverse junctions.

Also an analogue meter such as an Avometer could measure the forward and reverse junctions resistances.

This is good information for testing transistors - https://www.vintage-radio.net/forum/...ad.php?t=60938

David

[Station X]

See here for info on testing transistors using the diode test function of a DMM:-

https://www.vintage-radio.net/forum/...ad.php?t=42194

[Lef de art]

Thanks guy's. I will try this and I will post the results

[Lef de art]

I have removed all transistors and I checked them in multimeter. All shows to be correct. The multimeter understand them as diodes with no open circuit . At the same time I checked and two diodes that exist in the system but both are ok. I can't figure out why does not work

[DMcMahon]

Presumably the G268 comes out of Pause mode when you disconnect the round 4 pin connector of the 9095 from the G268 remote control jack ?

David

[Lef de art]

Yes it comes out of pause mode when i disconnect the 4pin round connector. Also comes out of pause and when i close the accessory from his on/off switch .

[TonyDuell]

First thing I'd check is the voltage on the red wire from the 4 pin DIN plug with respect to the ground rail of the device, just to be sure it's getting power.

[Lef de art]

I will check this later, when i will return at home .

[Lef de art]

Originally Posted by TonyDuell

First thing I'd check is the voltage on the red wire from the 4 pin DIN plug with respect to the ground rail of the device, just to be sure it's getting power.

Just checked the red wire and it gets almost 23 volts. I used ground on the device and on accessory. In both cases i had the same measurements.
The same voltage i find in the first leg of this transistor.

[DMcMahon]

This maybe the collector of the 3rd transistor (shown as OC80 on the schematic).

I am thinking this because when the transistor is not turned on/not conducting, the collector voltage (via the relay coil) probably would be close to the supply voltage, would expect the other 2 transistors collector voltage to be lower due to their load resistors etc.

As suggested in Post 2, transistor voltage readings may give a clue to what is happening/not happening.

David