Superstar 360FM issues

[Mudslinger]

The other week I bought a 360FM, which was sold as working and the seller assures me that this is the case. A picture on his advert showed the radio all correctly lit up.

The radio arrived before christmas, but due to me being away on holiday for 3 weeks I have only just had the chance to check it.

I have plugged it in, and only the S-meter illuminates.

The RX/TX light is off, there is no sound from the speaker and the channel display is off.
Keying the mic does nothing.

The radio wasn't packed all that great so there is a possibility that it has taken a knock during transit.

I will probably end up sending the radio to Nick for a fix, but out of interest has anyone seen this type of problem before and what could be causing it?

I will of course have a look for dry joints and stuff. The radio is in very good condition and doesn't appear to have been messed with.

Many thanks

[ch25]

No 8V in some areas, no doubt.
Chris

[14CS06]

Hello

Look first if the legs of the transistor TR41 (2SA 473) are not desoldered = it is the transistor fixed against the frame
After check on this transistor:
on its transmitter = the power supply voltage is about 13, 8 volts
On its collector = about 8, 4 volts
If voltages not compliant = transistor HS or chemical isolated at 10 volts short circuit



@+
Claude

[Mudslinger]

Thank you Claude

[Mudslinger]

Right, I have tried to measure voltages and something strange happens.

As soon as I connect the test probe to the pin closest to the audio chip the radio comes to life and stays working once the probes are removed.

However if I turn the radio off and back on it no longer works until I touch the probe again.

I have checked solder joints and they are ok, I have measured between the transistor heatsink and the radio chassis and it appears to be isolated correctly.

[NightProwler]

Now heres a crazy idea that a wise man on here once told me and it worked on one of my 360FM's when it went a bit crazy was to check the screws that hold the board into the chassis. I loosened and retightened them and it done the job, Although I cant remember what the problem was now but it worked Too many gins im off to bed now

[Mudslinger]

I did try that one. I have a feeling one of the components near the transistor has partly failed.

[astradyne]

Right, I have tried to measure voltages and something strange happens.

As soon as I connect the test probe to the pin closest to the audio chip the radio comes to life and stays working once the probes are removed.

However if I turn the radio off and back on it no longer works until I touch the probe again.

I have checked solder joints and they are ok, I have measured between the transistor heatsink and the radio chassis and it appears to be isolated correctly.

Are you applying a lot of pressure on the pins when you're using the probes? If you are it may be a nearby component, if you're only gently touching them onto the pins it's unlikely.

It could be a dry/bad joint and maybe worth cleaning it up and applying fresh solder. You may as well do the same for any nearby components.

Have you checked for damaged tracks around the 8V regulator? If it's taken a knock in transit it's possible that damage could have been caused.

[Mudslinger]

Yes just a light touch, I have resoldered the legs as well as some nearby components but it has made no difference.

I think it's an electrical issue rather than a mechanical one.

[astradyne]

It's strange how a light touch is all that's needed to power the radio. Maybe changing the regulator will help.

[163TM847]

Either the 2SA473 is blown or you have a short from an 8v source to ground maybe something is touching something it shouldnt and the light pressure is "un shorting" it.

[Mudslinger]

I think I will send it to you Nick. I have a couple of other radios arriving here soon so will send it with those.

[cb4ever104]

I've had a few that have had cracked solder pads/strips during transport , which were really hard to see . As previously stated , check around the 8V regulator .

[The Collector]

Instead of the probe, have to tried something non-metallic to see if it does it then? That may help narrow down if it's electrically shorting somewhere or just a dry joint perhaps?

[Mudslinger]

It doesn't happpen if something non metallic is used.

It is as if the high resistance connection between the transistor and earth is jumping it into life.