Seriously Kitsch SABA

[boiss]

Found some stuff here from Tasovision called" LUBRI-LIMP/0" which is supposedly a Tuner and contact dry cleaner. I will give it a few squirts and see what it is like tomorrow.
Cheers
Mike.

[boiss]

A few squirts of contact cleaner has freed up the switches. Still no AM/FM.
Checking back on AM one BF was O/C, swapped, all appeared OK but no sound.
Checked for LO using 7600, LW,MW and SW all OK. Touching I/P to front end at the Fet, brought in MW stations, also at the tuned L, dead at the Antenna I/P side though, all switches are OK Rather Odd !!!!!!!! Couldn't find anything immediately, this is going to be a bit of a pain I reckon. On the FM side dead in front of the stereo demod. IC (MC1305P) doesn't appear to be drawing any current. (Just happened to have a couple of MC1305Ps in the goodies box (As you do !!!!!)) .
Swapped it..... SOUND albeit distorted. swapped it for another with same result.

Getting Hum on both channels (Previously Intermittent) and one of the PAs is getting a bit warm. A quick check on an emitter R showed it was passing a few Amps. I noticed that part of the trimmer pot for the quiescent current had rusted away. It was 470Ohms, nearest in the goodies box 1K Ceramic. Swapped them in both channels and fitted a 1K in parallel.
Cool now without hum (Previous cap change was not necessary)
Everything is distorted now AM/FM and external Audio I/P.
A good time to break off and have a drink or 3 and think about what has happened.
Mike

[boiss]

Latest update;-
Audio amp probs with trimpots falling apart some dry joints and a very strange transistor, this measures on a DVM from each pin the same. Putting it on the HFE test provides variable but repeatable results as an NPN device but nothing if PNP selected. The Tranny in question was one of the drivers, substituting it restored the functionality.
FM now works quite well. AM is humming and showing signs of instability. The -24V line is only 22V and the O/P from the bridge rec is about 10V low, Changing the caps produced no change. It appears that something is pulling a lot of current from this line, according to the volt drop on the series 22Ohm res about 80mA. Will look at this prob in the next day or two. I reckon this will be the last thing I do with 3 legged fuses.
Instead of doing a FET grid dip meter next I'll do one with a DL96 if I can find one.
Mike

[Radio Fixer]

Admire your persistence: good stuff!

Gary

[Geaney]

Great work Mike, it will pay off in the end. Like many on here I share your views on the solid state stuff. Still, looks like a nice set so hopefully it will settle down and work reliably once the heavy work is done.

Cheers, John

[boiss]

Thanks Gary & John for the encouragement.
Another duff tranny, now the signal strength meter works along with the stereo decoder. Still got a nasty with the -24V supply(AM)??? The unsmoothed output at the reservoir cap is 10V low and the -24 is a few volts low. Removing the load everything is hunkydory. As I reconnect the various sections then the V drops and hum comes up.
The main cap is OK, the PSU appears to sink as much as it outputs, ie. 150 mA in and 70mA out. Offload, the current that is sunk is a few mA.
Have to get the scope out tomorrow and try and work out what is happening.
Mike

[boiss]

Using the scope indicated immediately what the prob with the -24V was, the ripple was 50Hz, checking the bridge rectifier once it was out showed an O/C diode. Changed for 4 x1N4007, Perfect, All voltages correct after tweaking the pot. Listening to the radio and also with an external signal, one channel was slightly weaker and tinnier. Changing a few of the caps in the pre-amp / tone control section made no difference. Hard wire bridge between the channels pinpointed it to the final pre-stage. Voltage checks showed yet another 3 legged fuse. Substitution , Sorted !! It worked fairly well before due to the feedback circuit, the fault being like having a low value Emitter cap.
The FM frequency indication meter has become intermittent and sticky, I took it apart but could see no obvious problem. I still have the problem with the poor AM sensitivity at the aerial socket. This appears to be down to the MW I/P coil, probably some shorted turns, maybe in the future I will look into rewinding but for now this is as far as I go and It is definitely the last tranny job I do on old stuff.
Problems with the sliders being broken and missing, I will try and repair with carbon fibre inserts and maybe make a slider knob.
Anyway it's all back together and I will use it as my workshop radio etc.
Mike