HMV 1621 radiogram

[jfisheresq]

Thanks folks, does anyone (Ed?) have a rough idea of how much a transformer rewind is likely to cost?

I've also got hold of a proper circuit diagram for this model, which I think, for me without any experience, is going to be a huge help.

And Chris, thanks - I may well take you up on that. I'm actually near Tenbury Wells, so not far at all.

I think some better photos might be helpful too, the sub chassis is currently restrained by a couple of wires which once de-soldered will allow a better view of it.
Jason

[jfisheresq]

Hi Everyone, I'm still working my way through this radio, and am learning lots as I go. Things are becoming clearer, but there's a long way to go. I've replaced a lot of the waxed capacitors, and the reservoir and smoothing caps, and had the output transformer re-wound.

What would be really useful is to have some advice about really obvious/important places to look for faults in relation to this particular radio, and some help in making further tests... I've got the circuit diagram in front of me, but it's not freely available, and am just wondering what the rules are for posting a photo of it - I don't want to upset anyone.

Thanks,
Jason

[Station X]

You're welcome to post extracts from the service data, but not the entire circuit.

[PaulR]

If you have replaced all the wax capacitors including the audio coupling ones then it should be safe to fire it up if you haven't already done so. Use your lamp limiter and see how it goes.

[jfisheresq]

Yes, I've replaced all of the wax capacitors, including the coupling capacitors, and any others which seem like they might be really important from looking at the circuit diagram. I've also replaced a couple of resistors which were not right, one was in the HT circuit from the rectifier, and was completely open, so I was hopeful that that was what was causing a lot of the problem. So, I've powered it up, through the lamp limiter... things are a little different, but the set is still pretty dead. There is a faint hum from the speaker now, and there is a slight crunch when changing between wavebands, where there was nothing before. The most worrying thing is that there was some arcing inside of the rectifier tube as soon as the lamp was bypassed, so I immediately turned it off. So... what are people's thoughts on that? Is there something to do with replacing the electrolytic filter and smoothing caps which could have caused this - something I may have done wrong or overlooked? Or could it be caused by a fault with the rectifier valve? This particular valve socket is a little loose, but there are no obvious signs of bad connections.

I haven't taken any voltage readings at all yet, but I'm getting more comfortable with what's what and where to take readings. And I'm still doing lots of reading and research - finding it all fascinating, and so getting a better feel for it. I suppose I'm just cautious of the high voltages.

Thoughts would be really helpful, as always.
Cheers,
Jason

[jfisheresq]

I should have added that with the test lamp in circuit (100w), the bulb was only dimly lit, and there was no smoking or smell from anything. I only bypassed the lamp for a second and noted the arcing rectifier immediately. With it fired up through the lamp, there was some audible sound through the speaker from rubbing the pickup stylus, when the waveband was set to gram. So it's certainly not quite as dead as it was before.
J

[Michael Maurice]

You need to start taking voltage readings, that is the only way you'll find out what's going on.

I take it, its dead on VHF.

Check the voltage on pins 1, 6 and 8 of V2 You will only get voltage on pin 8 on VHF

Pins 7 & 8 of V3

The fact that you're getting something from the gram, basically exonerates V4, V5, V6, V7.

The voltages are on the circuit diagram.

The screen grid resistors R6 & R12 are likely suspects for going high.

Let us know how you get on.

[Simon Gittins]

The arcing could be a faulty rectifier, it would be worth double checking your work though.

[jfisheresq]

Hi Everyone, Well, after many hours of reading and research, and lots of learning, and I've got a working radio! I can't tell you how thrilled I am. This set was so dead, and so daunting - and the help I've had here has been a major contributor to me not giving up (I don't tend to anyway!). My approach has been rather trial and error, and therefore has taken a lot of time, but I've been methodical and made notes about everything. FM is still very weak (tuning in to a couple of stations but very very quiet - weak valve?), but everything else is working very well, including the record changer which I've serviced. The pickup is fine with LPs, but there is some distortion with the 78rpm stylus, so that will need looking at in the future. This has really just been a bit of fun and a challenge, but I also seem to have acquired or found another 4 or 5 radios which need looking at, so I will no doubt be back for more help. The rectifier arcing was my fault - an electrolytic cap polarised the wrong way (!). But I've replaced the valve, and the capacitor. The screen grid resistors mentioned above were both very high, and so thank you for pointing those out. Anyway, I just wanted to thank everyone for their help and encouragement. What fun!

[PaulR]

Well done. It wasn't the easiest set to work on so you have done very well. If it has an ECC85 in the FM front end the that could be the cause of the weak FM. What is next, then?