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Telefunken M1 arcing on 240V supply


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#1 wills15

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Posted 29 January 2012 - 09:57 PM

Hey guys,

Posted this on stereo2go without much luck,


I picked up a Telefunken M1 in mint cosmetic condition the other day, however, when I connected it to the Australian 240V mains, it sounded as if there was arcing behind the tape VU metres - near the power supply.



The 'box is rated at 220V, but I only turned it on for a second, but it seems to have done some damage. Has anyone run one of these on 240V before?



Anyway, now when I run it with batteries, it shows low voltage on the battery display and doesn't have enough power to run properly. Was working perfectly on batteries before I plugged it in!



As you can imagine i'm spewing! Anyone able to clarify whether it was the voltage or another issue that caused the failure? Anyone else had this problem?



Thought I'd ask around before tracing the circuits with the schematics I've downloaded.



Any help much appreciated.

Will

#2 tshorba

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Posted 29 January 2012 - 10:02 PM

If that was the one off Gumtree in Melbourne, good score, I think the is only a couple of these known in Au

If you are in Melbourne i might be able to help

#3 baddboybill

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Posted 29 January 2012 - 10:08 PM

Hey guys,

Posted this on stereo2go without much luck,


I picked up a Telefunken M1 in mint cosmetic condition the other day, however, when I connected it to the Australian 240V mains, it sounded as if there was arcing behind the tape VU metres - near the power supply.



The 'box is rated at 220V, but I only turned it on for a second, but it seems to have done some damage. Has anyone run one of these on 240V before?



Anyway, now when I run it with batteries, it shows low voltage on the battery display and doesn't have enough power to run properly. Was working perfectly on batteries before I plugged it in!



As you can imagine i'm spewing! Anyone able to clarify whether it was the voltage or another issue that caused the failure? Anyone else had this problem?



Thought I'd ask around before tracing the circuits with the schematics I've downloaded.



Any help much appreciated.

Will

I know for a fact these run very low when running on battery's. They are better on AC :thumbsup: but I would say one of the fuses would blow before any damage would occur. What does it actually do when plugged into AC outlet :hmmm:

#4 wills15

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Posted 29 January 2012 - 10:27 PM

If that was the one off Gumtree in Melbourne, good score, I think the is only a couple of these known in Au

If you are in Melbourne i might be able to help


Yep it was, I offered him a little more as an incentive to find the battery compartment lid, which he did, so now it's almost mint!

When it's plugged it, all lights are illuminated but flicker, and it sound like something's sparking in the power supply, there's also popping through the speakers.

I could smell burning after it had been plugged in.

It doesn't just run low, I used new batteries, and the first time when I powered it up on them (only for a minute or so) it worked perfectly; now, the radio gets almost no signal, the battery meter shows low, tape rotates super slowly.

#5 baddboybill

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Posted 29 January 2012 - 10:48 PM

Well I would pop back off and look inside to see if any wires or components looked burned. :yes:

#6 wills15

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Posted 30 January 2012 - 05:51 PM

Well I would pop back off and look inside to see if any wires or components looked burned. :yes:


Will definitely give that ago, otherwise I'll hit up tshorba with a PM.

#7 sony_apm_fan

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Posted 30 January 2012 - 06:34 PM

Well I would pop back off and look inside to see if any wires or components looked burned. :yes:


Will definitely give that ago, otherwise I'll hit up tshorba with a PM.


I'm happy to have a look over it too... :yes:

#8 hemiguy2006

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Posted 05 February 2012 - 06:11 PM

There are fuzes inside the back of the box that determine voltage to be used ,versus a switch
For multi voltage operation.
You need to take off the back cover to check and see.
One fuse in the middle determines 220 v operation.
Two seperate fuses determines 120 volt.
I will likely have mine open again tommorow evening for bulb replacement if you need pictures of
These fuses.

#9 wills15

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Posted 06 February 2012 - 04:43 AM

Yeah, it's set on 220V, but the supply voltage is 240V - was wondering if this was a problem.

#10 wills15

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Posted 23 April 2012 - 05:02 PM

Hey guys,

I found the service manual on here and did some hunting around inside the telefunken. Found one of the electrolytic filter caps was shorted, and changed four others and the bridge rectifier (known to be unreliable).

Now...

Posted Image

Unfortunately I also found the pivot spindle for the tape button controls has broken away from the deck, so I'll either need to repair this or find a new deck chassis in the future.

#11 hemiguy2006

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Posted 23 April 2012 - 08:52 PM

AwsEsome you got it fixed!!!!!
I had the same happen with my cassette keys. Good luck finding a replacement deck though.
This seems to be a common problem as well with this radio. The plastic getts brittle then snap :
I rigged mine up with some jb weld and a zip tie to hold the rod in
Place while it dried. It is better than new now.

#12 wills15

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Posted 24 April 2012 - 02:16 AM

I had the same happen with my cassette keys. Good luck finding a replacement deck though.
This seems to be a common problem as well with this radio. The plastic getts brittle then snap :
I rigged mine up with some jb weld and a zip tie to hold the rod in
Place while it dried. It is better than new now.


Ah awesome, so the rod doesn't need to rotate? I might do the same thing - I guess you can drill a hole to put the zip tie through?

#13 Superduper

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Posted 24 April 2012 - 02:42 AM

If this unit was indeed correctly set to 220v as opposed to 110/120 (no external indicators of set voltage since it's done internally), highly doubtful that such a small difference in input voltage 240 vs 220 was enough to cause such failure. Chances are that the caps were on it's last legs and the small increase was enough to pop 'em. If shorted like you say, it would indeed cause a very low voltage condition. I wonder if they used marginally rated caps (voltage). I forget exactly but I think the telefunken has 49v rails when on AC so if the caps were 50, or even 63 volts, they are marginal for the application. Bumping them up to 90 or 100 volt caps would improve reliability if there's enough room to fit them. Rectifiers are probably OK but with the increased current draw from the shorted cap, they might be suspect and damaged so swapping them out was a good move.

#14 tshorba

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Posted 24 April 2012 - 09:23 AM

If this unit was indeed correctly set to 220v as opposed to 110/120 (no external indicators of set voltage since it's done internally), highly doubtful that such a small difference in input voltage 240 vs 220 was enough to cause such failure.


Au is bad for voltage from the wall sometimes, I have seen the supply in Melbourne swing from 225-260V, I have even heard of areas in Au hitting 280V and that is why I use a power conditioner on my Hi-Fi system. My current house sits around 233V and my old work (10 min walk away) used to sit around 243-246V

#15 Superduper

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Posted 24 April 2012 - 11:29 AM

10% swings in AC voltage is fairly common and the range you speak of sounds fine for a 240v system. But 280v for residential power??? That's very high, and very lethal.

#16 maxhifi

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Posted 24 April 2012 - 05:06 PM

10% swings in AC voltage is fairly common and the range you speak of sounds fine for a 240v system. But 280v for residential power??? That's very high, and very lethal.


I usually change out the electrolytic capacitors on anything over 30 years old which I intend to use regularly. If you have a decent desoldering tool it goes pretty fast - the bigger problem is sometimes accessing and removing boards.

I have Yamaha stereo equipment from the 70s which runs 50V electrolytics at high 40s. I know there's a margain of safety built into component ratings, andit seems ridiculous to push it but lots of manufactures seemed to anyways.

#17 wills15

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Posted 24 April 2012 - 05:39 PM

Yeah, I don't think it had anything to do with the AC voltage, that was just me hypothesizing...

I read on other posts here that the rectifier used is a selenium one, and it gets old and breaks down, resulting in sparking and weird issues, probably that, combined with the 30 year old electrolytics was the cause.

Everyone on here keeps talking about how well built this thing is, but of the boomboxes i've owned, this one has the most problems!
It's like a german car, looks solid but is actually unreliable...

#18 maxhifi

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Posted 24 April 2012 - 08:25 PM

Yeah, I don't think it had anything to do with the AC voltage, that was just me hypothesizing...

I read on other posts here that the rectifier used is a selenium one, and it gets old and breaks down, resulting in sparking and weird issues, probably that, combined with the 30 year old electrolytics was the cause.

Everyone on here keeps talking about how well built this thing is, but of the boomboxes i've owned, this one has the most problems!
It's like a german car, looks solid but is actually unreliable...


If you relate build quality to performance instead of reliability, German cars look a little better - hopefully the Telefunken has some superior performance too!

Selenium rectifiers will give off toxic fumes if you let them burn... if it burns don't breath it, and probably not a bad idea just to replace it as a matter of course. They also have a higher impedance than a silicon rectifier - I'm actually surprised to see one in such a new product, in US electronics like TVs they were gone by the middle 60s.

#19 Superduper

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Posted 24 April 2012 - 09:21 PM

Most boomboxes use IC's in the tuner, at least the multiplex decoder if not also the IF. They also use amp modules as opposed to discrete transistors in the outputs virtually eliminating the need for bias checks/adjustments.

The Telefunken, however, is mostly all discrete components and like points vs electronic ignition, or carburetor vs. EFI, it will require tuneups to keep it working in top shape and component values do drift over time. It's my experience that electronics that relies on IC's rather than discrete components are more reliable, and require less maintenance. Discrete components power some of the highest powered amplifiers and are easy to service since failed components can usually be substituted for an alternate part if the original is no longer available. IC's on the other hand is difficult to replace if the orginal module becomes obsolete. However, for boomboxes, they are perfectly fine and much more reliable.

Something interesting about the telefunken is that the darlington transistor outputs will operate over a very wide voltage range but for maximum performance, it simply must be tethered to AC. That's because on AC, the PS supplies 51.5 volts compared to 12 volts when on Batteries. That is the greatest disparity I've seen in operating voltage between AC and DC I've seen on a boombox. Even the Sony FH-7 has the ability to operate on AC or DC (with proper DC batter adapter). On AC the FH7 amp also is fed a fairly high voltage by boombox standards but on DC, it bypasses that amp completely and the DC adapter houses it's own internal amplifier since the AC amp won't even operate with the power supplied by the DC adapter.