Bush TR114 Major Struggles

[Nowhere-Man]

I removed today the decoupling capacitor and that blue power capacitor. This was new terrain as I have very little experience soldering on a PCB. As I said before, the main difficulty has been matching one side of the board against the other when removing a component. I also needed some way to clear the PCB holes for fitting replacements.

One mistake I did make was I used a bit too much heat on removing the large blue power capacitor so a localised bit of tracking had delaminated. Only a tiny bit still it's not convenient. Then I find a lot of people when that happens they run some wire along the damaged track to electrically connect the pathway. However, it would be nice if I could find a way to paint over some track paint if such an item is sold at Maplins?

I'm not very optimistic of my chances but I'll get some new caps tomorrow and should have them in soon. Might replace the transistor as well.

[Refugee]

You can indeed buy conductive paint however it is quite expensive and we rarely use it for track repairs.
Have you downloaded a circuit diagram yet?
Even if it does not have any voltages on it we can work them out so that you can check them.

[Nowhere-Man]

You can indeed buy conductive paint however it is quite expensive and we rarely use it for track repairs.
Have you downloaded a circuit diagram yet?
Even if it does not have any voltages on it we can work them out so that you can check them.

I don't have the diagram yet although I did find one I can use for the Ultra ACDC set.

I travelled to Maplins today to get capacitors and now I'm thinking I must have gotten something wrongly interpreted as they simply have nothing to match what I'm looking for. These are:

160 mF at 10 volts.

50 mF at 6 volts

30 mF at 12 volts

Also a spare transistor, possibly AC128 to maybe replace the OC81

Given they can find nothing that comes remotely close, it must be that the figures I read on the caps may have a point mark I didn't pick up on.

[Refugee]

The actual values of those capacitors are not critical and the voltage just has to be greater than the battery voltage.
160uf use 220uf 25 volt
50uf use 47uf 25 volt
30uf use 33uf 25 volt

We are not yet sure the transistor is faulty just yet as it was measured in circuit and the biasing resistors will have produced false readings.

[Nowhere-Man]

The actual values of those capacitors are not critical and the voltage just has to be greater than the battery voltage.
160uf use 220uf 25 volt
50uf use 47uf 25 volt
30uf use 33uf 25 volt

We are not yet sure the transistor is faulty just yet as it was measured in circuit and the biasing resistors will have produced false readings.

Thanks. I popped back to Maplins just and now have the caps. Only snag is they're not film ones so polarity may be an issue - that is I'll have to be sure they're fitted pos and neg. The ones I removed had a centre and side lead and I did jot down a few notes.

I bought a PNP transistor just in case while I was at the store. The original transistor is indeed fine as I resoldered some fine wire back to the leads and it seems fairly robust. I will probably put it back in situ.

I forgot to say, by the way, I noticed one capacitor was puffed at the top so it now seems an electrolytic was knackered. It could well be the case that the cap went kind of wild as I was attempting to fire up the radio and it all led to heating of the speaker. It could even be the case it was nothing I did wrong but the cap was just a weak link so I got a burst of stations coming in and then fading out.

Anyway, I'm very appreciative of all the terrific advice you guys hand out here and will keep plodding on with a possible hope of a future fix. Keeps me away from the DVD movies.

[Refugee]

The radio will most likely be positive earth so that the capacitor locations will have the positive sides going to the positive battery terminal. Just check with the meter on the lowest ohms range to confirm this and you should have no trouble getting them the correct way round.

[Nowhere-Man]

The radio will most likely be positive earth so that the capacitor locations will have the positive sides going to the positive battery terminal. Just check with the meter on the lowest ohms range to confirm this and you should have no trouble getting them the correct way round.

I'm a bit wary of cobbling up the electrolytic polarity. I would rather have gotten film caps but Maplins only had electrolytic ones. The caps I removed had long upper leads and the lower lead was short. Going by the pics and my notes, the longer upper leads bend down from the top and are facing forwards so I conclude that the positive leads will be closest to me. I already did a few tests with the meter taking resistance from both perforations in the board between the solder pad and battery positive. So, logic would suggest the lowest resistance to + will be the capacitor + longer lead.

Still, it would make life simpler and surer if I was just going to use a film cap.

I still need to fix the track of the PCB and may just use superglue to pin down track edges and some tiny strands of wire I have. Then solder a bridge but away from the superglue area and finally test continuity.

I haven't done particularly well on this specific project and got caught out by lack of experience but I did my best to make better diagrams and may be lucky enough to get it going - time will tell.

[Refugee]

Your measurements do indicate that it is positive earth. Old electrolytic capacitors used to have the negative lead bent round the can. At least you now know how to get them back in the right way round.
If all the capacitors are fitted back in correctly there is a good chance it will work again.
Resistor lead offcuts are good for repairing tracks. Superglue makes a nasty vapor if it gets heated so I avoid it in places where it might get near a soldering iron.

[tiv48]

Here is part of the circuit to see how it compares to yours

Rob T

[Yorkie]

I don't want to appear critical, discouraging or dismissive of your efforts, but think that most of us, before embarking on any work on a radio - especially a transistor radio with a high component density on a PCB, would first obtain the service data, and would go about diagnosing any faults in a methodical way before making assumptions about what might or  might not be faulty based for example of folklore about AF117s. True, the problems they can pose are well documented but we shouldn't jump to conclusions - often they're not faulty at all.

The most productive approach is methodical diagnosis. The first thing to do is to measure the voltages as compared to the circuit to highlight any variances which might pinpoint the cause of the fault.

In the case of the Bush TR114 the Bush service data runs to 7 pages, and though it shows component placements, isn't too descriptive as to the PCB track layout. I'm not normally a fan of Trader Sheets, but in the case of the TR114, the two-page Trader Sheet shows an X-ray of the track layout so you can identify key components to enable you to test, and if need be, unsolder and remove them.  If the PCB is SRBP rather than fibreglass, as it most likely is, the adhesion of the tracks will be poor, so you need to be quick at unsoldering component leads and use a pencil tip iron and de-solder pump. Never be tempted to 'wiggle' a component when de-soldering, to free it up or sure as heck, you'll lift or break the track.

If you don't adopt a methodical approach to fault diagnosis, you'll inevitably disturb, and possibly damage components that aren't faulty, and may introduce faults that weren't there in the first place.

You can do a quick check if the oscillator is running by placing a set with the same IF frequency alongside the TR114 and turning the Tr114 tuning cap across the same waveband as the other set to see if you hear 'whistles'. If you do, it's an indication that the mixer/oscillator in the TR114 is working.  

On a dead set which has an earphone socket, open circuit contacts are often the culprit and bridging out the socket can check that out, but in your case, the overheating could possibly be caused by C31 being leaky (in the electrical sense). That can only be checked by taking it out of circuit. The audio stages in that set are a reliable design and pretty standard in many sets of that era. Everyone has their own approach to servicing, but personally, I use a signal injector/tracer to pinpoint faulty stages. If you inject a signal into the slider of the volume control and hear a loud tone from the speaker, that's an indication that the audio stage is working. (Even scratching the slider tag with a screwdriver should be audible in the speaker).  If you get no tone, and apply the tracer (just a small amplifier) to the slider of the volume control and can tune stations, that means the RF/IF stages are working.  If you don't hear stations, you can work your way with the tracer to the front end of the set - for example checking at the collector/base of each transistor to isolate the faulty stage.

In the TR114 - as in the Bush TR82 - if the audio stages are working, but no stations can be heard, a likely culprit is a faulty detector diode (referred to as 'MR1' in the TR114 circuit), which is an OA90 germanium diode, hidden in IFT3.  It's quite a palaver to get to that diode, but there's no need to dismantle anything. Leave the duff diode in place, and a replacement diode can be tried externally across pics 1 & 2 of IFT3 (the right way round!) and if that brings a dead set back to life, it can be permanently soldered externally between pins 1 & 2.

You can get an excellent Velleman kit to make a signal injector tracer from ESR Electronics for about a tenner inc P&P:

https://www.esr.co.uk/velleman/k7000.htm

You just need to add a little speaker, on-of switch and some sockets, put it in a box and make a probe, then you can use it on any valve or transistor radio. There's a pic of one I made below.

As I said at the outset, the last thing I want to do is to dampen your enthusiasm, so the above comments are meant to be helpful - not critical, because it's evident from your comments that you are putting in as great deal of effort, with this set and your Ultra valve radio, though without a structured approach, and without at least some basic test gear and service data, which is reducing your chance of success. You're treading a well-worn path, down which we've all trodden, you can rest assured about that!

Every good wish in your endeavours.