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-   -   Philips SBC850 Multimeter (https://www.vintage-radio.net/forum/showthread.php?t=153107)

Station X 24th Mar 2020 5:51 pm

Re: Philips SBC850 Multimeter
 
I'm not suggesting you dismantle anything.

You could fit a battery and see whether the resistance ranges work. Just select each range in turn, touch the test leads together and see if you can zero the scale at the right hand end using the OHMS control.

Then how about measuring the voltage of a 1.5V and 9V battery?

DMcMahon 24th Mar 2020 10:57 pm

Re: Philips SBC850 Multimeter
 
Quote:

Originally Posted by giacomo16v (Post 1227771)
I think the color of resistance are all brown for 1,2,4,5 ......the middle is to much burned and dont know if that is one information for understand something......example.....in commerce the only one resistance that you can find is one resistance all brown if the 1,2,4,5 are brown....somebody have an idea

You must have very good eyesight if you can distinguish 4 brown bands on this burnt resistor !

DMcMahon 25th Mar 2020 12:24 am

Re: Philips SBC850 Multimeter
 
1 Attachment(s)
I can now see from post # 6 where you think there are 4 brown bands, I am not so sure myself.

Some of the other resistors look like they have 6 bands and others 5 bands, so the burnt resistor could be a 5 or 6 banded resistor but the sixth band is a temperature coefficient value, so it does not matter in terms of the resistance value determination.

From your high resolution photo my old eyes are still struggling with some of the band colours on the various resistors, but from what I can determine they do not obviously appear to be similar values to the Philips UTS-001 circuit resistors.

If the burnt resistor does have 4 browns bands with a band in-between, then that would mean the resistor is 11X (first, second and third colour band digits) multiplied by 10 (4th brown band = the multiplier of 10) where X could be anything between 0 and 9.

In this example the most logical colour for the middle band would be black (0) this then would be 110 multiplied by 10 which is 1.1kohms which is a preferred (standard) resistor value. The 5th (outer/last) brown band being a +/- 1% tolerance band.

But resistors in DVMs may not be preferred values, i.e. they may be special values to suit the meter calibration.

Have you tried measuring the burnt resistor to see if any resistance value can be measured ?

giacomo16v 25th Mar 2020 10:44 am

Re: Philips SBC850 Multimeter
 
I still have not tried to measure the burnt resistance because unfortunately I do not have a multimeter with a charged battery to be able to do it, however under the microscope the bands of the burnt resistance can be clearly seen that there are 5, and fortunately the 4 external to the central one can be seen well that the color is brown. Your deduction on the color of the central band gives me hope and I thank you for understanding my little electronic reasoning, and more practical. Now I will look for a way to create a 3 volt battery to power the other multimeter I have at home and measure the burnt resistance. thanks a lot DMcHamon

Crowella 25th Mar 2020 3:09 pm

Re: Philips SBC850 Multimeter
 
Hi, sorry for the late reply, the PCB will come out, I will send what info I can, but need to find the meter again first!

giacomo16v 7th Apr 2020 6:11 pm

Re: Philips SBC850 Multimeter
 
Hi Crowella! Sorry but only now i have see your answer. So thank you, i'm waiting for your good news!:-)

Gtman72 26th May 2020 7:22 pm

Re: Philips SBC850 Multimeter
 
Greetings to all from Italy.
I think this discussion is the only one in the world that talks about the SBC850. And of course those who find it are those who have a broken SBC850. Unfortunately, I am no exception, the same broken resistance, soon I will post some photos.
It would be very important for me to repair this multimeter, because it has a great emotional value for me.
I hope that a solution can be found together.

Gtman72 6th Jun 2020 8:45 pm

Re: Philips SBC850 Multimeter
 
3 Attachment(s)
I took new photographs of my SBC850 and I noticed that it is less burnt than yours, I can partly trace the colors, by exclusion you can get there, can you help me? So we finally fix them!

Station X 6th Jun 2020 8:52 pm

Re: Philips SBC850 Multimeter
 
Red denotes that the value begins with a '2', but that's not much help.

Is the resistor's value written under it on the Printed Circuit Board (PCB)?

Station X 6th Jun 2020 9:00 pm

Re: Philips SBC850 Multimeter
 
1 Attachment(s)
Your burnt resistor is intact in the attachment to post #15, so a forum member with better knowledge of colour codes than me should be able to determine its value.

Gtman72 6th Jun 2020 9:19 pm

Re: Philips SBC850 Multimeter
 
I looked with a powerful lens, after red there seems to be brown, and the last one is definitely brown. I believe that other users can be of help since the resistance above them is burnt, instead on mine you can still see the colors. It's already a step ahead, isn't it?

Gtman72 6th Jun 2020 9:32 pm

Re: Philips SBC850 Multimeter
 
There is something written on the PC, but it doesn't read, I should remove the resistance to see if the writing has burnt or is legible.

Station X 7th Jun 2020 11:24 am

Re: Philips SBC850 Multimeter
 
Six band resistor calculator here:-

https://www.digikey.co.uk/en/resourc...or-code-6-band

Try reading he values of the good resistors and compare them to what's printed on the PCB.

DMcMahon 7th Jun 2020 12:36 pm

Re: Philips SBC850 Multimeter
 
Quote:

Originally Posted by Station X (Post 1256795)
Your burnt resistor is intact in the attachment to post #15, so a forum member with better knowledge of colour codes than me should be able to determine its value.

Using the calculator I make it 143 ohms 1%, starting with brown, yellow etc, if one tries to read it from the other end, the yellow band then is not a valid colour for the % tolerance.

DMcMahon 7th Jun 2020 12:48 pm

Re: Philips SBC850 Multimeter
 
Actually looking at the chart in my Post # 23, yellow has a 4% tolerance, so in that case reading it from the other end (the red band) it is 210 x 1,000 so 210kohms at 4%.

This makes it confusing. There is supposed to be a spacing between the bands to enable one to know which is the first/start band but difficult to see the spacing.

factory 7th Jun 2020 1:38 pm

Re: Philips SBC850 Multimeter
 
The lower value makes more sense with the failure mode, the higher value would have much less chance of being burnt from measuring voltage with it set to the current or resistance ranges.

David

jonnybear 7th Jun 2020 2:16 pm

Re: Philips SBC850 Multimeter
 
1 Attachment(s)
I have just found this circuit in a drawer, I know it is a schematic for a Philips multimeter but unsure of the model. It might help locate the part you are looking for or give some direction.
John

Station X 7th Jun 2020 2:27 pm

Re: Philips SBC850 Multimeter
 
Very good!

If Gtman72 can tell us the resistance and full-scale deflection of the meter in his multimeter we'll know whether it's the correct diagram.

Several resistors there with values commencing 14.

factory 7th Jun 2020 2:56 pm

Re: Philips SBC850 Multimeter
 
I don't think that diagram is for the SBC850 as it shows a separate socket for the 2.5A range. Also looking through the pictures in this thread the SBC850 has a 100K pot and x3 ranges instead of the x2.5 ranges shown on the diagram.

David

stuarth 7th Jun 2020 3:18 pm

Re: Philips SBC850 Multimeter
 
Not the correct diagram Iím afraid. It shows a 20k/V version of an SBC 851.

The diagram shows a separate AC/DC switch rather than AC and DC ranges at different positions of the main switch, 2AA cells rather than 1, 4 Ohms ranges rather than 3, and different current ranges. Resistor values will be different.

However, assuming a reasonably conventional circuit with a universal shunt, and comparing the front panel picture in post 3 with the resistor values visible in the attachment to post 15, we can hazard a guess at the missing resistor value.

The resistors at the top of the picture are obviously the voltage range resistors, and unsurprisingly are undamaged. These resistors show that this is a 20k/V meter (for DC).

Resistors close to the missing resistor have values of 143, 1430, and 1.41 Ohms

Unless Iím very much mistaken, these are the universal shunt resistors, and the missing resistor is between the 30mA and 300mA switch positions and should be 14.3 Ohms. The resistors between the two pots are 2840, 274, and 27.4 Ohms. These would match up the resistance ranges seen in post 3 with current ranges of 0.3mA, 3mA, and 30mA. There is no 0.3mA range on the main switch, but the top of the 1430 Ohm would give that range for the highest resistance range.

If this theory is correct, DC voltages will read high by 20 to 30%, current ranges of 30mA and below will read very high, and current ranges of 300mA and above wonít read at all.

If you just short the stub ends of the missing resistor, the voltage ranges should read correctly. If you fit a 15 Ohm resistor, the resistance ranges should be OK, but the 30mA current range will read a bit high. Adding a 330 Ohm resistor across the 15 Ohm resistor should give near enough 14.3 Ohms.

Then again, I might be very much mistaken!

Stuart


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