HR2510 about 15ma of final bias before mic is keyed.

[Low_Boy]

Only showing bias on final before keying not driver. The radio will put out 30W. Bias diode is good. All associated disc. Caps and resistors check good. Unless I missed something. VR112 good. I believe if the final was bad I would not be getting good power like I am. Any ideas?

 

[nomadradio]

Trouble with the transmit-receive power-supply switching. If the transmit side fails to shut completely down in receive mode, this is one side effect. Takes not much more than a Volt leaking out in receive to tickle the final's bias circuit.

73

 

[Low_Boy]

Thank You Nomad. I started thinking along that line but I remembered this happened on a 148 GTL and it turned out to be a disc cap in the final section on that radio. Time for me to look at the block diagram and schematic.
Thanks.

 

[Handy Andy]

Per @nomadradio - I second the notion, but make sure too - that all your hardware in that area is tight - small currents from loose hardware not taming the IF noises and provide shielding - can turn those MRF477 on like a switch - and the only way you'd know it - was by you hearing it slowly baking itself to death by the "carrier" that formed and seems to swoosh up and down the bands - would kill your receive. It self-oscillated that easily.

 

[DoctorAudio]

Yes, on a 2510, B+ is on the driver and final even when the radio is off.

 

[Handy Andy]

I'm working on something regarding how the infamous UNIDEN engineers took to the task of the problem on their next radio - the 2600...

Something interesting there - partly to them, for they know it exists, a type of current loop ringing effect that even MOSFETs are prone to encounter under use, or used in - inductive loading.

But because of single sided layouts and the 2510 phasing out - they just did this up for their 2600 radio and they then just seemed to end the project...

I'm only putting this out there for their efforts in the 2166 Drivers NFB circuit was not enough.

Hr2510...

Hr2600


​

Might want to review parts and values used...

Locate C118 (Q32) - so think and act accordingly...

 

[Low_Boy]

I always wondered why they designed that so if the radio was switched off there was still power to the back end. Possibly they could not fit a bigger on, off and volume pot in the radio. LOL.

 

[Handy Andy]

Power supply thru the switch - the MRF-477 can easily take 7 amps - not too many simple On-Off Volume switches are built for that kind of power pull/draw - at least in the size that fits that radio!

 

[Low_Boy]

They did it on the Jackson. I think. but that is a bigger radio.

 

[nomadradio]

Yes, on a 2510, B+ is on the driver and final even when the radio is off.

Power to the collector circuits. Not to the base circuits. That comes from a regulated source, by way of the transmit/receive switching. The final and driver are effectively switched off when there is no base current. Using the power switch only to control the stuff that does turn on the driver/final saves money on the power switch and the wires feeding into and out of it.

73

 

[NZ8N]

They did it on the Jackson. I think. but that is a bigger radio.

The original Jackson DX had direct power to the Final and Driver, it was the precursor design to the HR series.

 

[Low_Boy]

Talk about cheap. I believe it is just a bad idea leaving power to the final and driver transistors all the time.

 

[Handy Andy]

Ever own a Ford, GM, Chrysler, Yugo - or Nissan?

There's more than one piece of equipment that leaving the battery connected all the time - isn't the most effective means to avoid voltage drops.

 

[nomadradio]

We observed a unique vulnerability with this setup in the HR2510. OTR drivers would park a truck at a plaza, go inside for a while and come out to a smoke-filled cab. And a radio too hot to lay your hand on. Seems a sufficiently-large radio parked next to him keyed up and kicked the 2510's final into oscillating.

Until it either tripped the fuse, or started smoking heavily.

Not so common now, but when that radio was popular with drivers it would happen every year or two, seemed like. Learned to recommend pulling the power plug when the truck is parked.

73

 

[Low_Boy]

We observed a unique vulnerability with this setup in the HR2510. OTR drivers would park a truck at a plaza, go inside for a while and come out to a smoke-filled cab. And a radio too hot to lay your hand on. Seems a sufficiently-large radio parked next to him keyed up and kicked the 2510's final into oscillating.

Until it either tripped the fuse, or started smoking heavily.

Not so common now, but when that radio was popular with drivers it would happen every year or two, seemed like. Learned to recommend pulling the power plug when the truck is parked.

73

I have heard this about the 2510 in the past. I know I do not know how long it was pushed in. I thought things were very quiet for quite a while. Turned out the TX button was in. Lol other drivers were listening to the underground garage along with me for who knows how long. Not really but good thing the radio does not have vox.