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Old 9th Oct 2017, 10:25 am   #21
crackle
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Default Re: Hacker Radio:Motorboating - RP25

I think I would double check the plug to the amp board, wiggle at around when the motorboating is happening. This thread http://golbornevintageradio.co.uk/fo...56211#pid56211 is to do with the Sovereign 3, but it does show that the earthing of these sets is important, and I have had similar problems with the 5 pin plug and motorboating on a RP25.

Mike
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Old 10th Oct 2017, 4:30 pm   #22
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Default Re: Hacker Radio:Motorboating - RP25

Update:
1. I've re-cleaned the 5-pin plug contacts and inspected for dry joints. No change.
2. I delved deeper into the I.F.amp (502) and saw that the 2 screws holding it in place were missing. These effectively earth this board and other boards. The motor boating has now stopped BUT I cannot tune into any LW or MW stations
3.Just as worrying is the following: I tested the quiescent current of the amp board (205).

Now I hope I did it correctly: (Snipped the test link; bridged contact 4 and 5 on the female side of the 5 pin socket and reconnected the 5 pin lead. Connected my simple Maplins type multimeter (set to mA) between one of the battery terminals and the power lead. It should read 3mA. Mine: 17.5mA for FM and 8.28 mA on AM, BUT this was before I had properly earthed the IF board as described above. The new readings after this mod were: FM:17.4 mA; AM 14.2 mA).
I suspect a leaky capacitor on the AM side -but all the electrolytic ones appear to have been changed (and orientated correctly).

Please has anyone any ideas?

AND

If I cannot mend it does anyone live in or near Sheffield who could do it for me (at a price of course)?
Thanks,
Richard.

Last edited by Bonky28; 10th Oct 2017 at 4:52 pm.
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Old 10th Oct 2017, 5:08 pm   #23
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Default Re: Hacker Radio:Motorboating - RP25

I think you're getting confused about measuring the quiescent current.

To measure the quiescent current of the output transistors you open the test link and connect a milliameter in place of _that link_. Short pins 4 and 5 on the 5 pin socket to remove the audio signal and measure the current.

What you are measuring is the battery current. Well the battery current less the output transistor current (as that link is open). Reconnect the link and put the milliameter in series with the battery to measure the complete battery current.

According to the service manual the battery current should be 18-20mA on AM, and 20-23mA on FM. Given that 3mA of that is the output stage quiescent current (which you have removed by opening the link), your currents seem pretty much correct.
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Old 10th Oct 2017, 5:18 pm   #24
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Default Re: Hacker Radio:Motorboating - RP25

I agree, those readings are very plausible.

Use your signal generator to inject a 465kHz modulated signal at the detector diode, then work backwards touching the transistor collectors and bases until it disappears.

Don't give up yet.
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Old 10th Oct 2017, 6:13 pm   #25
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Default Re: Hacker Radio:Motorboating - RP25

Quote:
Originally Posted by TonyDuell View Post
I think you're getting confused about measuring the quiescent current.
You are absolutely correct. I had done it correctly before but totally forgot! I'm an idiot! Apologies!

Thanks,

Richard

Quote:
Originally Posted by paulsherwin View Post
Use your signal generator to inject a 465kHz modulated signal at the detector diode, then work backwards touching the transistor collectors and bases until it disappears.
Thanks Paul; I'll give it a go in the morning.

BW

Richard
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Old 11th Oct 2017, 7:21 pm   #26
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Default Re: Hacker Radio:Motorboating - RP25

Quote:
Originally Posted by paulsherwin View Post
Use your signal generator to inject a 465kHz modulated signal at the detector diode, then work backwards touching the transistor collectors and bases until it disappears.
Paul, another 'thick' question.
Which one is the detector diode? (Is it D1 (a BA102) on the T304 board?)
Is 'working backwards' towards the aerial or loudspeaker end?

...apologies...

BW

Richard.
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Old 11th Oct 2017, 7:31 pm   #27
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Default Re: Hacker Radio:Motorboating - RP25

On the manufacturers service data the AM detector diode is CR1.
What Paul meant was, work forwards to the RF end of the radio circuit, by touching the signal generator on the collector of T4, then T3, then T2, then T1 noting what happens to the signal.
The point at which the signal disappears shows the transistor downstream towards the AF end is the faulty one.

Mike
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Old 11th Oct 2017, 7:37 pm   #28
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Default Re: Hacker Radio:Motorboating - RP25

Thanks Mike; appreciated!

BW

R
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Old 12th Oct 2017, 1:48 am   #29
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Default Re: Hacker Radio:Motorboating - RP25

Quote:
Originally Posted by paulsherwin View Post
Replacing the AF117s in the AM IF stages with 2N3906s isn't a straightforward thing to do and it may be causing the instability. You can sometimes get away with it, but silicon transistors have very different characteristics and can be too lively without other component changes. Do you have any germanium RF transistors that you could try?
This is so true.

If you can get some AF178's they make excellent replacements, there are usually some on UK ebay most of the time. These have identical or just slightly superior properties to the AF11x series but they never get the Tin whisker effect as they are resin filled. And they look good as replacements on the pcb.
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Old 12th Oct 2017, 7:16 am   #30
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Default Re: Hacker Radio:Motorboating - RP25

Thanks for that; I'll look around. At present the AM section is completely dead!

BW

Richard
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Old 12th Oct 2017, 10:12 am   #31
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Default Re: Hacker Radio:Motorboating - RP25

Ordered! Thanks. R
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Old 15th Oct 2017, 5:56 pm   #32
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Default Re: Hacker Sovereign II RP25A Dead on all Wavebands

Very interesting as I have a similar model with a similar loss of AM. Injecting a signal to the diode in L8 produces a tone but the C and E of T4 to T1 produce no tone at all. I have some replacement trannies in the post so will hope my fault is as easy to rectify as yours.

Thanks for the inspiration!

Richard
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Old 19th Oct 2017, 5:46 pm   #33
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Default Re: Hacker Sovereign II RP25A Dead on all Wavebands

Ignorant trier here again...

Re:Hacker Sovereign 2. (RP25). I have got rid of the motor-boating. It works fine on FM but not on AM. I have now replaced T1 to T4 on boards 502 and 501 with more authentic ones (AF178s). But still no sound. Most of the electrolytic caps have been replaced.

I have a sig gen and a Vellemann signal tracer (now working properly after early issues). I can get sounds from some components on both boards, I was advised to start at the detector which I think is on board 502 and under the 'can' of L8. I have tried to unsolder this item with no success. Imagining where the diode pins may be on the pcb, I do get a sound from one 'end' and not the other. I don't know if this is correct(?)

I am at a loss to know how to move on. I know I need the discipline to follow the circuit diagram properly and not just stick a probe in at random, but I wondered if anyone could give me some advice...

(I live in Sheffield but periodically visit Golborne and Bath. If any kind soul would like to peruse the 'giblets'I would gladly pay).

I hope it's acceptable to copy this on two other websites (Golborne and HackerGroups).

Yours,

Richard
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Old 20th Oct 2017, 12:04 pm   #34
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Unhappy Re: Hacker Radio:Motorboating - RP25

Quote:
Originally Posted by Radiocruncher View Post
Have you cleaned the FM switch with switch cleaner as that could cause issues? I had to take one apart recently and clean it with emery paper as switch cleaner didnít do the job.
No, no no!

To anybody else reading this, please don't follow this advice!

And don't use Brasso, either.

The switch contacts are silver plated and it is vital that the plating isn't removed, ever.

Use Silvo (the liquid, not the padding) or a similar product designed specifically for cleaning silver, eg: Goddards Long Term Silver Polish.

It is vital, for long term reliability, to preserve the silver plating. Usually a thin silver line will appear at the point of contact as the switch is operated. In really stubborn cases, assistance in the form of light pressure from a suitable object such as a matchstick can be used but it is vital that the silver plating is not abraded in any way.

When the switch is clean, the remaining Silvo can be blasted off by an application of switch cleaner.

Back in the 60s, working in an industrial area, switch cleaning, particularly of VHF TV tuners, was a daily routine. Finding contacts stripped back to bare brass usually mean't the end of the set's life as the tuner would need cleaning virtually on a weekly basis.
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Old 20th Oct 2017, 3:18 pm   #35
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Default Re: Hacker Radio:Motorboating - RP25

I use a slither of card (birthday card or similar) laced with Servisol to clean delicate switches and relay contacts. If you are able, release the pressure between the two contacts sufficiently that you can move the card back and forth, but that it doesn't bind (grind to a halt and buckle). Never use out and out abrasives.
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Old 20th Oct 2017, 3:38 pm   #36
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Default Re: Hacker Radio:Motorboating - RP25

Using a signal generator, you will get sound from one end of the detector diode but not the other. This is normal and shows the detector is working.

Now move back through the IF module, touching each transistor collector in turn with the signal generator probe. You should be able to hear sound at each one.

Double check that you have wired the replacement transistors correctly. Have you checked the transistor voltages in the IF module?
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Old 20th Oct 2017, 3:44 pm   #37
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Default Re: Hacker Radio:Motorboating - RP25

What frequency is the signal generator set to?

Lawrence.
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Old 20th Oct 2017, 5:10 pm   #38
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Default Re: Hacker Radio:Motorboating - RP25

I think I tried two: 5kHz and 465kHz (?)

Thanks,

Richard
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Old 20th Oct 2017, 7:20 pm   #39
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Default Re: Hacker Radio:Motorboating - RP25

5 kHz is an audio frequency. Most simple sig gens won't provide output at that frequency (though some may modulate at that frequency - around 1kHz is more usual).

465kHz is the frequency you should use. You may need to vary that a little if the IF alignment is a bit off.
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Old 22nd Oct 2017, 5:11 pm   #40
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Default Re: Hacker Radio:Motorboating - RP25

Hi all. Once again, many, many thanks for you all on this site and Golborne's for all the help.

Update:
I am no further forward.

1"David Potter:
One question.
Is the AM oscillator actually oscillating?
One simple method is to place the radio under test, near to another working radio, tuned to a medium to weak station up the high end of the band, 1.2 meg and above. Tune the test radio lower down the band to see if you can pick up the oscillator of the test radio on the working radio, (you will soon know if you find it).
You can practise with two working radios first. Tune slowly as it will be very narrow."

I couldn't find any signs of the pick-up from the oscillator in a working radio.

2. Voltages on the collectors of Tr1 to 4
There are no voltages (!) except on TR1 (On another board) where it reads 1.27V

3.The HT line on the 502 board should read 9V. It reads 2.23V

I thus thought that the switches must be at fault, but shorting the pins on the pcb made no difference.

I haven't yet tested the 'dropping' resistor R13 but if this were faulty then why do I get a voltage on the collector of TR1 (via R3)?

I can't see how board 502 gets its +ve supply from.

A tell-tale sign may well be that the whole set is slow to warm-up ( perhaps 30 secs or so) - even on FM (which works well)

Thanks,

Richard.
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