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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

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Old 14th Mar 2021, 5:54 pm   #41
Simon Gittins
Heptode
 
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Location: Cornwall, UK.
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Default Re: Dynatron Music Center - Help Please

It's quite possible that there is no power getting to that section!

I don't have the service data for that model, being able to see the whole of the FM section would help but that would be stretching the above rule. Perhaps a moderator could advise whether this would be ok?
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Old 14th Mar 2021, 6:44 pm   #42
BotleyJoe
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Default Re: Dynatron Music Center - Help Please

I think I've now found the power supply to the board. This section of the wiring diagram...
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...corresponds to this area on the board where the red wire is connected via a 15 Ohm resistor...
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The voltage at the red wire is 74.7V but there is no mention of what the correct voltage is in the data sheet. I think I may have gone as far as I can now with my limited knowledge. To be honest I'm a bit worried about frying something and putting the unit beyond repair.
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Old 14th Mar 2021, 7:48 pm   #43
Simon Gittins
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Default Re: Dynatron Music Center - Help Please

That's difficult if the correct voltages don't seem to be given.

The voltage is coming in on the red wire connected to R612 (15k) and then goes to R448 (33k) which then connects to the positive terminal of C457. It may be worth checking what the voltage is at the junction of R448 and C457.

The other way of getting it fixed would be to post a request in the Repair and Restoration Services Wanted section.
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Old 14th Mar 2021, 8:22 pm   #44
BotleyJoe
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Default Re: Dynatron Music Center - Help Please

I'll have to take the chassis out of the case to get at the junction but the voltage off the top of C457 is 18.7v (assuming C457 is the blue one in the photo above). Does that help?

I'll try to check the junction under the board tomorrow; what voltage should I expect there?
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Old 14th Mar 2021, 10:39 pm   #45
Simon Gittins
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Default Re: Dynatron Music Center - Help Please

That's the correct point to measure (the top of C457) and 18.7 volts sounds about right. There is no need to check under the board, that's the junction of R612 and R448.
Does the data sheet give any voltage details at all?
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Old 14th Mar 2021, 11:22 pm   #46
BotleyJoe
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Default Re: Dynatron Music Center - Help Please

Not that I can see, but I'll read it all through again tomorrow. Unfortunately I still have to remove the board. R456 is cracked and the only way to get at the underside of that section of the board is to slide it to the rear and away from the frequency tuner. I have ordered a new one.

I think it might be time to call in a "responsible adult".
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Old 15th Mar 2021, 11:11 am   #47
Simon Gittins
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Default Re: Dynatron Music Center - Help Please

Reluctantly, I think you may be right.
Another thing to be considered is that the BF195 transistor shown in the second picture of Post 42 is of a "Lockfit" type and these are increasingly troublesome. If you put "Lockfit" into the search bar at the top of the page you will find lots of posts including this one:
https://www.vintage-radio.net/forum/...d.php?t=144412
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Old 15th Mar 2021, 11:37 am   #48
BotleyJoe
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Default Re: Dynatron Music Center - Help Please

Many thanks Simon.
There are 6 x BF195's on the board. The one in the picture is TR404. How would I go about testing these components? Can it be done in situ?

On a positive note, I have managed to remove R456 without damaging to board.
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Old 15th Mar 2021, 12:29 pm   #49
Simon Gittins
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Default Re: Dynatron Music Center - Help Please

As you are in the process of changing R456, you may as well see whether this has made it work. If it was open circuit you may be lucky.
If it still doesn't work, you can try gently tapping each of the Lockfit transistors in turn, this may restore results briefly and identfy the faulty one.
Otherwise, it's voltage measurements or checking them with the set unplugged using your AVO meter and the method on this page:
https://www.vintage-radio.com/repair...or-faults.html
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Old 15th Mar 2021, 10:46 pm   #50
100series
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Default Re: Dynatron Music Center - Help Please

Hey Joe.
VHF worked before. Unless you picked it up and threw it down some stairs with frustration there is nothing wrong with it. Nothing has changed since when it last worked.
Once you start removing items or twiddling things on the mobo anything (worse) is possible.
It is lack of use which is the cause of the FM not being reliable.
As I write I am listening to another (different Dynatron,with an SRX 25 amp/innards) playing Wille Nelson" sitting on top of the world" on VHF.
An hour ago there wasn't even any hiss. Worked out that one channel of the power amp is dead. Stuck H/phones to confirm this just in case its a loose wire to the speaker outputs, which, unfortunately it isn't, but found out it was a well worn DIN socket was why no sound came from it, the other channel is dead. End of.
So wearing the H/phones I do another of my foolery. Get the tuning knob and while listening spool it right to the right extremity (108) and try to force it further ( > 108) than normal and sometimes (and I cant explain why) I start getting hiss. I then spool it back and I now find my FM is working perfectly, and can tune it as a now healthy VHF tuner. Tonight this has worked with this particular junk Dynatron.
I am listening to it right now.
I dont know if you have made all that impossible by doing what you have described above but if not give it a try. You dont have to.of course, but it worked for me half an hour ago.
I then thought I will post this.
Good luck.
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Old 15th Mar 2021, 10:52 pm   #51
BotleyJoe
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Default Re: Dynatron Music Center - Help Please

Thanks for the suggestions. I reset everything to the way it was so I'll give your suggestions a go. I don't have any headphones so I'll have to work out another solution.

It was working perfectly until I fitted the turntable. That was the only thing I did and I can't understand how that would have changed anything. Bur maybe it did?

I still get excellent reception on MW & LW so the issue is only with FM.

The unit is now in my spare room while I'm waiting for the resistor to arrive and I'm to give my self (& the machine) a break and go back to it later in the week.

Thanks again for the suggestions. I'll post an update later in the week.
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Old 16th Mar 2021, 2:26 pm   #52
100series
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Default Re: Dynatron Music Center - Help Please

No problem, no hurry and another Diet Coke if it works. Or maybe a pack of Truffle flavoured crisps from Waitrose.
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Old 16th Mar 2021, 5:24 pm   #53
BotleyJoe
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Default Re: Dynatron Music Center - Help Please

As luck would have it, one of the guys I volunteer with at a local charity is a retired electronics engineer and he is going to have a look at it for me tomorrow f. Fingers crossed!
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Old 20th Mar 2021, 12:48 pm   #54
BotleyJoe
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Default Re: Dynatron Music Center - Help Please

Quote:
Originally Posted by BotleyJoe View Post
As luck would have it, one of the guys I volunteer with at a local charity is a retired electronics engineer and he is going to have a look at it for me tomorrow f. Fingers crossed!
Do luck there unfortunately, but he did replace the cracked resistor for me. So we tapped all the transistors as suggested above but noting, not even a crackle.

I've have found that if I connect my DAB radio to the tape input the system will pipe everything the DAB can receive at much better quality than the radio.

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But that's not what I was hoping to do so I've decided to cut my losses, fit the beautiful (new) Lenco GL75 deck and sell the unit on to free up some space for another project.

Look out for pleas for help on that one

Many thanks to everyone for all your help on this one.
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Old 20th Mar 2021, 12:56 pm   #55
Edward Huggins
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Default Re: Dynatron Music Center - Help Please

The GL75 will need care in setting up. We can advise and/or you can go to LENCO HEAVEN for additional advice.
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