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

[Bonky]

Thanks; I can't see any signs of the faults you describe`.


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!

Adding a separate 9V supply to the board does not result in anything except crackle and motor boating.

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

[Murphyv310]

Hi Richard.
A transistor set doesn't need time to warm up. Now that could be caused by something drifting, a component that is failing when cold or something failing leaky that partially clears when switched on.
It's hard to diagnose what's wrong especially like Terry in that I have no manual.
I could of course repair it for you for just the cost of post and parts, happy to oblige and do a write up here on the work done.

The resistor you mention is not likely to be the problem. You'll be reading through it and the other circuits. Something is pulling excess current and that's why your voltage is low, hence the quiescent current is up.

[Refugee]

If it is that bad you could bring it here to be fixed.
It certainly will not get wrecked in the post.

[Murphyv310]

I think we should leave the final decision up to Richard, Ref.
He may wish to plug away himself or take up mine or your offer.
I do though offer a five years warranty and a free bottle of champagne with my repairs.   

[Refugee]

I did say could without bothering to add the words "as an option".
There does appear to be a short circuit of some kind that needs to be found. A transistor the wrong way round is another thing that needs to be looked for.

[Bonky]

Thanks both of you for the kind offers.

I think I'll give it a few more days and then will no doubt avail of your very kind offer to take it off my hands!

BW

Richard

PS I hasten to add that the set never worked on AM; it's just that'll my alterations/investigations have made no difference.

BW

R

[Bonky]

I have added some pics on: https://www.vintage-radio.net/forum/show...367&page=3

BW

Richard.

[Refugee]

It looks like the collectors of the transistors might be touching the IF cans.

[Bonky]

I'll re-check;thanks.

[Mark Hennessy]

But these aren't TO5 transistors with the case connected to collector - these have a screen connection, just like the AF117s did. So assuming the leads have been correctly identified when they were fitted - which is an important assumption, naturally - then the cases touching the IFTs shouldn't cause a problem.