Portavision-5

[Joe]

I'd more or less forgotten I'd got this until I was reminded by one of Chris's threads. It's a a Realistic (ie Tandy) Portavision-5, catalogue number 16-7058.

[attachment=1583]

I got it new in 1986 and it worked fine until a few years ago when I switched it on, there was a 'plop' in the speaker but that was all. This is what it still does.

There's nothing that's obviously been over-heating or anything and any advise about where to start would be handy. I circuit diagram is too long a shot to even think about.

[attachment=1584]

Cheers
Joe

[tiv48]

hi jo have you checked the plug in psu. if ok check the joints on the power input socket, also joints around the lopt and the line output transistor. thease were common falts when they were used by lorry drivers look the same as road star?

[Joe]

Power is certainly getting into it but I'll check the other joints you suggest.

Thanks
- Joe

[Joe]

I've not been able to do much today but I've just had another look at it.

I can't find any bad joints and have redone those of the power socket and LOPT just to make sure all is well.

The diodes Jamie mentioned are fine too.

I found it was drawing a current of 12mA so there seemed to be some life in the beast. I tried injecting a signal at the volume control and, yet again, nearly got deafened by 4kc/s belting out at full amplification a couple of inches from my ear. I don't know if this means anything or not.

I've had a dig around for a schematic with my predicted lack of success. It isn't helped by there being other things called a "Portavision-5" including a colour set and a TV-radio-cassette.

It's far from important, it isn't a RADIO when all's said and done, but makes an interesting diversion.

Thanks for the suggestions so far.

- Joe

[tiv48]

do you have a scope if so see if there is a wave form at the base of the line output transistor
rob t

[Joe]

I don't have a 'scope but had a poke around the output transistor, or at least the three-legged device I take to be the output transistor, with a crystal ear-piece but couldn't hear anything.

I think that having neither a schematic or any previous experience (the only things I've previously done in my life have been to resolder an aerial socket and bypass a broken main switch) the best thing is to put it aside pending the acquisition of either. At least I've ruled out anything stupidly obvious.

Thanks, all
- Joe

[danny]

Hi its probrably the regulator thats failed if you folow the supply from the power socket you will find a power transistor check the voltages on all three legs. it should regulate at about 11v if this is missing you can try the set with a bench supply set to 11v do not exceed this voltage or the crt heater may get zapped. this shouldnt take long to sort out . i have a similar set somewhere if you need help i will get it out and trace the cuircuit for you. Danny

[Joe]

Thanks, Danny. I'll have another look at it when I've tidied up a bit and have room to move. I think it will be something obvious as one day it just didn't switch on - there was no spectacular bang or anything.

Cheers
- Joe

[Joe]

It looks like you're on to something. Whilst measuring the voltages I momentarily sorted something and it gave a whistle like it as warming-up. I know from experience that my bench supply hasn't got enough 'umph' to power it but that also made it whistle at least.

This drawing shows what voltages were where when connected to its own PSU, relative to ground, from the track side of the PCB and a drawing of the three-legged beastie in question:-

[attachment=1685]

I haven't been able to find any information on a devise with the part number KD880 so far so any help on that score would be appreciated.

Cheers
- Joe

[tiv48]

h i jo a d880 is a 3 amp silocon power transistor
rob t