Hacker RP 25 -Motorboating now now AM and high quiescent current

[Crackle]

UKVRRR is not such a good place to add pictures, they get reduced rather a lot to about 600 x 450, the detail is hard to see.
On here there is no such excessive image reduction, but I suggest be sensible on file size. I normally limit my images to 1280 x 960.

Mike

[Mark Hennessy]

Yes, JPEGs can be up to 2MB in size. The number of pixels is not limited, just the file size...

[Murphyv310]

Yes this must be one of the most generous sites for the size of uploads.
On a couple of car forums I'm on I did use Photobucket, now you have to subscribe to link to forums, I now think it's best to upload to the forum for continuity.
Sorry for going off topic.

[Refugee]

Those transistors just looked like regular TO5s.

[Mark Hennessy]

Yes, I thought the same at first...

Here's an image of them: https://www.langrex.co.uk/products/af178...rs-x-2pcs/

[Bonky]

T1 to T4 are now AF178s. (PNP, TO72 packages)

R

[Bonky]

Update. I hope I'm not being a nuisance here...

Trying to pick up the oscillator from a nearby working radio doesn't seem to work on my Sov2,however, injecting a 1kHz signal on both sides of R14 does elicit a tone from the Hacker speaker.

These are the voltages on T1 to T4. There are NO voltages on the Collectors!

T1 B 6.28. E 8.18
T2 B 7.08. E 7.55
T3 B7.13. E 7.55
T4 B 6.46. E 6.79

I've ordered a new detector diode and various replacement parts so will wait for those to arrive...unless anyone has any further helpful hints...?

Thanks,

Richard.

[pwdrive]

No voltages on the collectors...try to figure out why....its easy.

T1 looks ill according to that measurement.

Lawrence.

[Murphyv310]

Hi.
Yes T1 is wrong. I'd also hold fire on the diode, very rare for them to fail unless someone had flashed it. The oscillator is certainly not running, could be a duff cap, faulty oscillator transformer or even the transistor or its connections.
P.S. you are not a nuisance.

[Mark Hennessy]

Well, since you mention it, running the same thread on 3 different forums can become a bit awkward. Whenever this has happened in the past, it's always led to confusion - especially if the person asking the questions is a beginner.

First of all, it is correct that there are no voltages on the collectors. Or rather, there is 0V at the collectors.

To help us understand you better, to what extent are you able to follow the diagram?

For the benefit of others who commented on this earlier, please look at the schematic. It is available via the Yahoo Hacker Radio group.

The other voltages mostly look OK at a glance, but T1 is a bit suspicious.

Why are you changing the detector diode? I strongly advise that you don't do that until you have firm and conclusive evidence that it is faulty. They are very reliable - I've repaired hundreds of these sets and can't recall the last time I had to replace them. In addition, it is buried inside the IFT, and so requires a fair bit of skill to replace without causing more faults.

You also mention "various replacement parts". Why?

With the greatest of respect, you are treating this radio like a modern garage treats obscure faults on cars. This "scattergun" approach of randomly replacing parts is not the correct way to repair a radio. AF117s aside, there might only be one or two faulty components, and you need to find them using logic. Every time you change a part you risk creating a new fault. Stop it!

It's likely that the oscillator is the problem and the IF amp might well be OK. Or perhaps not. Either way, we need to do some diagnosis to decide where to look. So, to save me having to re-read all the threads, have you managed to inject a 455kHz tone yet? Apply it to C8 in the first instance, and come back to us with the results.

If you don't have the means to generate 455kHz, then either obtain a suitable generator, or leave the poor set alone!

I repeat: do not change that diode. Yes, it might well be faulty, but we don't know that yet. If you damage the IFT, they are very hard to find.

Sorry if some of that seems to be bit blunt, but for the sake of the poor set, we need to focus.

In some ways, it's unfortunate that Hacker sets have a reputation of being easy to work on. It's true that mechanically, they are superb. But electrically, they are complex sets, and need just as much skill as any other set when they do go wrong.