Hacker RP38A; very obscure fault.

[ekcobeach]

Arghhhhh, frustration or what.I have a Hacker RP 38A which utterly refuses to work standing up. Lay it down, and it performs perfectly but if you lift it very slowly and gently into the upright position, it cuts out.

Now I'm at my wits end because I have checked, poked prodded and even thumped it a few times but nothing has given me the slightest clue as to what's causing this. It's almost as though it has a built in mercury switch.

The odd thing is that laying face down, ie speaker down, it works fine but if you lay it reverse side down, not a peep. Loose wires, internally broken wires, dry joints, definately not. It's something else. So come on you experts, put me out of my misery and make some suggestions - PLEASE I'm willing to try anything.

Regards, Colin.

[Paul Stenning]

Is it completely dead when it's upright? Is any current being drawn from the battery? Do you get a buzz when you touch the wiper of the volume control?

If it is drawing current but completely silent, check the earphone socket (if fitted). The contact that disconnects the speaker could be a bit loose. Try connecting an external speaker directly to the connections on the PCB to prove this.

It may even be the fine wires from the tags to the cone on the speaker, though I would expect the sound to break up in the working position (especially at higher volume) if it was that.

If it's not drawing any current, check the external DC input socket (if it has one) for the same thing.

At least with "totally dead" it is likely to be power or speaker connections. Amplifier alive but no reception would be more tricky to track down.

It may come down to normal fault tracing with it positioned where it doesn't work, to narrow down where the problem is.

[Darren-UK]

If I remember correctly with this set, look in the back at the righthand battery. This battery stands upright and there's quite a clutter of wires very near the top of the battery, the earphone(?) socket and the end of the pcb.

Could the problem be caused by something here ? the battery tilting slightly when the radio is turned over, thus moving a wire that otherwise shorts when the radio is upright ?

[ekcobeach]

Hi Guys, Thanks for the input thus far. I currently have the main board out of the case and the problem lies somewhere on this bit.If i turn the board slowly from horizontal to vertical ,the power appears to drain away. Any clues? Please don't suggest loose wires or the like.

[Steve_P]

Can you prop it up vertically to make a few tests. First, the On/Off switch! Then see where the 18V supply goes. I notice that there is a Plug and Socket arrangement between two boards. Look at this carefully. There's also a test link between 18v and the Push-Pull output transistors. And there's another Socket arrangement, J51 in series with the speaker.

Faults like this drive you mad. Advice from an Expert - Go for a cup of tea and come back to it refreshed. You might then land straight on it!

Cheers,

Steve P

[yestertech]

Could it be a loose/broken slug in an IFT, given the face down/face up difference ??
Andy

[ekcobeach]

Hi Andy, That was my very first thought but being as these are screw in slugs,i dismissed that idea,unless you know different!

[stuie319]

Hi there,

Absolute long shot, and I'm sure your pushing and prodding would have disproved this already but could it be a hairline print fracture thats managing to make when the board is horizontal? can you prop the board up and make some DC checks?

Regards
Stu

[yestertech]

Just checked the Hacker data for this set - sometimes I find these have been annotated for stock faults - NOTHING !
Given that at least the fault is repeatable, you'll need to test stage at a time to see where the fault lies. ( inject AF, IF , and RF consecutively and repeat ) measure battery current at the same time.
Loose washer under a screw somwhere ? Faulty preset ? Loose contact in a switch wafer.... you'll nail it sooner or later ! A.

PS how about linking out the on/off switch, just in case ?

[johnlees]

I had exactly the same problem with a radio I gave to Paul Sherwin (can't remember which, but it was a valve mains one). It worked fine face down but suddenly went absolutely dead, i.e. switched itself off (yes, the dial lights went off as well) when it was up-righted. I never did find the answer to such a seemingly simple problem. Did you, Paul ?

[Mike Phelan]

Talking about slugs falling out, the ferrite cup on my RP25 LO coil (L5?) was loose; wonder if Colin's IFTs have these in them?
As it seems to be completely dead, maybe not.
What I would do is to run a lead to things like the VC slider for a start or the IF PCB LT supply and measure these when the set goes off - that will get you nearer.
Could it be an AF11? transwhisker? They often respond to tapping.
HTH

[Paul_RK]

Originally Posted by Mike Phelan

Could it be an AF11? transwhisker? They often respond to tapping.
HTH

No, those stages are all silicon in the RP38A. Can't say I've met this symptom in a Hacker. I do have it in a wedge-shaped mains ITT-KB set which I was told when I bought it would only work upside-down and had been happily doing so for years. A couple of years have passed since then, so I await Colin's success with interest

Paul

[wireful3]

Originally Posted by ekcobeach

,the power appears to drain away. Any clues? Please don't suggest loose wires or the like.

Does this mean a gradual fade away or sudden cutoff at some point?

If the latter I would not dismiss a hairline fault in the pcb track just yet. As you say the vigorous treatment should have shown up dry joints on leads but the tracks are different.
I had a similar problem with a plug-in stereo decoder. It worked for about 10 mins and then cut out. I could find no faults on either board even with careful examination. Removing the supporting clamp however solved the problem so I can only assume thermal distortion was bending the board slightly. I never found a faulty track but it has worked now for over a year.
I have just looked quickly at my 38A and it looks as though the supply from the on off switch goes to the board very close to the mounting screws which might be significant.

It might also be useful to know what happens to the battery current when this is going on.

[G0PKH - Pete]

What I would tend to do in this situation, is to temporarily solder some fine wires to the voltage rails in the set and attached a meter to them, that way you can determine exactly what is going on.

Pete

[Gordon]

I had a similar fault on a Hacker Sovereign which turned out to be a bad contact on the external 'dc in' socket (I don't know if you have one fitted) and although I moved the main board the wire to the socket must have moved causing the fault to appear and disappear.
Gordon.

[ekcobeach]

Hi All, Many thanks for your suggestions.I am now a step closer to the problem. When i short the contacts on the on/off volume switch,the radio comes back to life so i'm suspecting a dodgy wiper contact or something similar. Further investigation required. Colin.

[ekcobeach]

Having removed the on/off volume switch,bit of a fiddly job, I stripped down the pot and hey presto,one side of the switch contact fingers broken in two and floating,causing the intermittent contact. Thanks again for the tips,i'm now off to the Radio parts wanted section. Regards, Colin.