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Beogram 6500 fuse constantly blowing

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Steve
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Steve posted on Tue, Jul 26 2016 7:15 PM

Hi 

 

I've recently moved house - and my Beogram 6500 has blown two fuses. It was working when I moved in, but every night when I come home the turntable won't power up and fuse blown. The first time I replaced fuse it played fine all evening.. but then tonight I come home and the new fuse is gone. Is this a power / surge issue in my apartment block.. or something problematic with the electronics?

 

any advice appreciated!

steve

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kimhav
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kimhav replied on Sat, Apr 10 2021 4:19 PM

D1 is open. Measuring C2 (470 uF) gives reading (increasing ohm value) and IC1 pin 9 to ground indicates that it's closed (low ohm reading).

Dillen
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Dillen replied on Sat, Apr 10 2021 4:32 PM

IC1 shorted then, if you're sure about those readings.
That's quite unusual.
Can we see a photo of IC1?

Martin

Dillen
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Dillen replied on Sat, Apr 10 2021 4:34 PM

Could also be that D2 has shorted. Lift one end and put your ohmmeter across it.

Martin

kimhav
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kimhav replied on Sat, Apr 10 2021 5:03 PM

Martin, I misread what you wrote; I measured IC1 PIN1 to general ground. Measuring IC1 pin 9 to IC1 ground and pin 9 to general boards ground it open (and IC1 looks fine) and regarding the diodes:

D1 = 631 and switching polarity gives 1609 instead of OL so it's bad.

D2 = 122k ohm (measured directly over it)

D9 = 630 and switching polarity gives OL so it's good.

 

 

Dillen
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Dillen replied on Sun, Apr 11 2021 7:07 AM

Sounds fine then.
Sure you fit the correct type and rating of fuse?
Is a RIAA fitted in your Beogram?

Martin

kimhav
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kimhav replied on Sun, Apr 11 2021 8:30 AM

Yes, using slow blow 500 mA fuse so that should be fine as well. But, for now I'll just need to fix that bad D1 diode (any idea was this one gone bad?) and going  to check the mentioned transistors above also. Yes, the 6500 has a RIAA fitted, but as mentioned the fuse blows only if the PCB1 board is connected to PCB2. Haven't removed PCB1 board one yet from the turntable but going to do this today to do the work.

kimhav
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kimhav replied on Sun, Apr 11 2021 12:31 PM

Here is the full PBC1-board which in general looks fine:

But there are two areas on the boards which shows signs of heat; first area is the resistor cluster R38 - R45 in the corner area:

Including around R3 and TR1:

So going to check the various surrounding components but any pointers and hints is appreciated - As it has been so far from everyone in this thread.

Dillen
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Dillen replied on Sun, Apr 11 2021 12:58 PM

Is the solenoid plunger broken?

Martin

kimhav
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kimhav replied on Sun, Apr 11 2021 1:43 PM

No the solenoid plunger looks fine and moves smoothly when applying gentle movement to it. And to be mentioned I did use it for couple of hours last weekend before it stopped working once it was done playing a record; meaning moving the sledge back to 'parking' mode. Obviously something spiked in the PCB1. Currently I've replaced C2 (470uF), C28 (2.2uf) and D1 & D2 (1N 4002) including TR3-5 (BC337-35).

Checked the rest of the transistors which seems within expected measurement range when checking values between base and collector/emitter with exception for TR6 (92 PU51) which measured between base & collector (658) and base & emitter (301). So seems that TR6 needs to be replaced as well if this isn't the expected behaviour of this PNP transistor and that 92PU51 can be replaced by 2SA1593 or BD508.

kimhav
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kimhav replied on Sun, Apr 11 2021 6:46 PM

Here is a guess for what to be looking at next; since TR6 seems to be a bit wonky I would assume that due to this that the motor might be drawing too much from the 5V which could potentially or most likely also blew D2 which is used to regulate the 5V for the most of the parts on this board based on that D1 was verified to be bad as well.

While I could test by removing D2 and test but don't really have and 12V to feed with, well could use a 9V battery plus some resistor to bring down to appropriate level to verify if it's working order. Could also remove TR6 and measure the 5V over D2 to see what it shows. Or I just go for replacing Tr6 and D2 and try then. What is your take on this?

Dillen
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Dillen replied on Sun, Apr 11 2021 7:43 PM

Will the platter and carriage motors both rotate easily by hand?

Martin 

kimhav
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kimhav replied on Sun, Apr 11 2021 8:32 PM

With the belt and everything in place, then Yes, it rotates easily by hand. Measured up all the resistors around the motor control most of them comes out fine with the correct values but there are a few ones which comes out with odd values including that the silkscreen doesn't match up what is printed on the component side:

R1 = Can't locate this one but viewing the silkscreen printing it indicates R1 on the solder side were R3 is located.

R2 = Measures 30k and increases so this one is bad. Should be 100k

R3 = Measures 220 ohm which aligns with the schematics (see also note for R1)

R5 = Measures 55k. Should be 100k

R10 = 300. Should be 10k

R11 = Measures 300. Should be 560.

R12 = Measures 300. Should be 560.

R31 = Measures 29k3. Should be 82k (this one should be good since it's regulated by R32 (45RPM)).

R34 = Measures 25k2. Should be 34k8 (this one should be good since it's regulated by R34 (33RPM)).

Might be that all of the values are all fine based on the collective forum experience and that the schematics aren't correct.

Dillen
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Dillen replied on Sun, Apr 11 2021 9:15 PM

If you are mesuring the resistors while they are in circuit you cannot trust the readings, because you will be measuring
through other components as well.
I'm sure they are all fine.

Martin

kimhav
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kimhav replied on Mon, Apr 12 2021 9:08 AM

Yes, aware, was more of an indication if something sticks out and to verify whether any of the resistors didn't work proper. But, seems that most of them are within the expected tolerances and none of them are bad and not working. So for now I'm going to replace also D2 and TR6. TR6 seems to be a bit trick to find including the suggested replacement; any additional thoughts on good replacement parts for TR6?

Dillen
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Dillen replied on Mon, Apr 12 2021 9:16 AM

The correct part:
Beoparts-shop

Martin

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