HI Fred, your questions will be answered. Expect it to take a while with lots of signal tracing, head scratching, etc. Lots of fun remains. Don't give up!

Just for example: Yes, today I am also working on freebee ST-6. It has, and err had, various modifications to sort. Remember much of the ST-6 was supplied in kit form and invited customization.
I thought best to try to get back near factory. So a field added relay on the back panel was removed. There are several connections to a 25 pin D-sub connector which appeared to be for RS232 level signals or polar signals. Plus some other controls wired to a small vector board mounted behind the front panel having an assortment of transistors and resistors likely for computer or remote functions TBD.  Added through the front panel are three additional toggle switches. Some have useful features, one for afsk mark/space selection another marked cmpt/normal.
Now troubleshooting...
The power supply had a blown fuse. The loop switch transistor Q301 and diode D307 were destroyed and in pieces. The front panel Receive lamp was open and transistor Q602 weirdly intermittent. The afsk oscillator AK-1 had a bad 10 ufd cap, was not real stable and had horrific radiation that was hand sensitive and made my scope go crazy. For the stability issue I checked the +12 VDC supply and saw it was only +11.0 volts. Normally not a big deal, but the 8.2V Zener on the AK-1  was only reading 7.8 Volts! That 1 volt made a difference! Long story short, in the DC power supply I added two diodes in series with D507 adding 1.2 volts to the base of Q501. Now have 12.2V. Better would be to change the zener. For the radition generated by the toroids? I added a 220 uufd cap across base and emitter of Q7. That quieted things down tremendously.

I did check the AK-1 board with a spare. Both had the radiation issue. I also checked the power supply by removing the extra cards and with a spare. Both had 11 or 11.2V. So neither was an anomaly. Both were modified as mentioned. I am now getting closer to checking the receive filters.
That's all for now.

73, John W1AN


On 19-Feb-24 21:30, Fred Weksberg wrote:

Hello everyone,

I am trying to restore  HAL ST-6, but it’s not exactly like to pdf manual I have.

The motor connector at the back is a 8 pin tube socket, and the fuse holder at the front has been removed and replace with an inline fuse holder behind the front panel.  The panel hole now has a toggle switch (on-off-on) and it looks like a 3PDT.

When I turn the unit on the receive light is always on. The space light is on, even with no signal if the “new” toggle switch is in the middle or up position.  If I flip this switch down then the space light goes off and the mark light goes on.

The meter will peak to 0.6 on a 2125 (actually 2140) signal and will peak to 0.62 on a 2295  (actually 2320) signal.

The filters need adjustment, but at least they are 180 apart.

The wiring inside the switch looks original.

There is an additional board in the extra option slot.

 

I don’t know what this is doing.

In addition, when I am in standby and I peak a signal I don’t hear the relay activating.

Sound like multiple problems.

Any suggestions please.

 

Thanks, Fred Weksberg VE3WN / VE3PIE


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