Hacker Radio:Motorboating - RP25

[paulsherwin]

Those voltages are very, very wrong. You will need to follow the +ve line from the on/off switch to the module and work out where the volts are going. Either there is a high resistance in the +ve line somewhere or something in the module is drawing excess current and pulling the voltage down.

Have you measured the current being drawn under normal operation? It should be about 20mA at low volume.

[Bonky28]

Hi, on FM I get 17.57mA rising to 18.24mA as the set warms up.
On AM I get 16.67mA.

I ran a separate 9V line to the board. I got crackles and motor-boating. I'll work back from the switches later.

Thanks,

R

[paulsherwin]

Those current figures are plausible and suggest nothing is pulling down the +ve line. You should continue to investigate the circuit voltages though, as there is obviously something seriously wrong there.

[Andrewausfa]

This has been nagging me since I saw your post yesterday, I'm sure I'm not the only one puzzled by the statements ' The whole set is slow to warm up' & 'As the set warms up'. This is a transistor set, as soon as you turn the switch to On, it should work immediately.

What actually happens when you turn the set on at the volume control switch? Is there any difference in behaviour between when you switch off/on using the volume control and then with the set on and 'working', switch it off and on by dis - and reconnecting the batteries? Can you describe?

Andrew

[Bonky28]

Originally Posted by Andrewausfa

This is a transistor set, as soon as you turn the switch to On, it should work immediately.

What actually happens when you turn the set on at the volume control switch? Is there any difference in behaviour between when you switch off/on using the volume control and then with the set on and 'working', switch it off and on by dis - and reconnecting the batteries?

"This is a transistor set, as soon as you turn the switch to On, it should work immediately."
I know; and I'm sure it did once!

"What actually happens when you turn the set on at the volume control switch? "
..Nothing --not even on FM.

"Is there any difference in behaviour between when you switch off/on using the volume control and then with the set on and 'working', switch it off and on by dis - and reconnecting the batteries?"

None that I can tell.

I'm about to spend another (wasted?) hour on it now so will do other simple tests.

Richard.

PS. I can't read the CBSE letters on the pcb for TR1. I know I can work back from the circuit diagram and obviously 'S' is to earth but it would be nice to have the letters confirmed. Does anyone else have an early Sovereign2?

Thanks for your interest!

[Andrewausfa]

If nothing happens with the Off/On switch how are you getting the set to work at all?

Just trying to discount a dodgy power/volume control, not unknown in these! I was wondering if you were turning it on, waiting for a few seconds and then the set was powering on and that equated to your 'warming up'. I've had ones where the switch had some lag, possibly due to old grease.

I doubt it's the cause of your main troubles however.

Andrew

[Bonky28]

Hi Andrew; again, many thanks.

It works OK on FM although it still takes time to warm-up. Very strange! I've used switch cleaner on the on/off switch.

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

On board 601 (the switchboard) I get 17V on one side of R13 (good),but only 5.47V on the other side - rather than 9V. I started checking the resistors. R13, R3 and R1 are all within limits (all measurements in situ). However, R1 should be 6.8k and is only 2.62k. I will replace it -when I can get to Maplins but fear that that's not the end of it!

T1 I took out and put back again. Looking from the 'battery' end to the tuning dial I have soldered the tags in this order: E,C,S,B. T2,3 and 4 are wired EBSC - I can read the letters on the PCB - but not for T1).

Thanks again,

BW

Richard

[paulsherwin]

EBSC is correct for an AF11x series. You should make sure that you have wired the replacement transistors correctly. It sounds as if TR1 is miswired.

[Andrewausfa]

I still don't get the 'warm up' bit

Anyway, if you've got an RP25 and you say R1 is 6.8k on the switchboard, it's not, it's 1.2K. R2 is 6.8K. But I doubt they'll be a real cause at the moment. I'm with Paul, I'd venture something, somewhere is miswired. Some clear photos may help internet diagnostics.

Don't get discouraged, keep going

Andrew

[Bonky28]

Apologies. R1 reads 1.19k;it's R2 that reads 2.62k when it should be 6.8k.

BW

Richard

[Bonky28]

Since I replaced T1 on the AM board the 'warm-up period' has thankfully disappeared when the set is pre-tuned to FM (!).

I've ordered some more parts - mainly so I could get the Vellemann tracer to work with an automatic probe (thanks David!). However I think I'm more than likely to ask others much more expert than me (not difficult) to peer into the giblets.

BW
Richard.

[Bonky28]

Originally Posted by Andrewausfa

Some clear photos may help internet diagnostics.

Andrew,
Thanks for that. Here are some pics (I hope). Purists will be disgusted that I've temporarily soldered T1 on the copper track side of the PCB (SO much easier...)

[Bonky28]

and 3 more...

Richard.

[Bonky28]

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.

[ms660]

Originally Posted by Bonky28

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

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

T1 looks ill according to that measurement.

Lawrence.

[paulsherwin]

Are you measuring voltages with reference to the +ve or -ve rails? This is a PNP module, so ground is +ve. If you are measuring with ref to -ve then those readings look plausible.

[mhennessy]

No, it's negative earth. The collector voltages are all OK