Philips GM5655 V2

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Philips GM5655 V2

Postby Harry Dalek » Sat May 09, 2015 9:25 pm

LIke my other scope a while back this one from 1959 has been sitting around for a while ,doesn't work but i knew the CRT was ok as you see a green out of focus dot move acoss the crt when powerd off .
I had a look to see if there are any circuits to this scope and there are but documents tend to be in dutch i think all 8 of them .
Any case i opened it up to have a look and i could see i was not the first vistor to view this beast ! all valves light up... but parts of it i am not impressed at the wiring ,
Some ones put in a pot connected around the power supply area it was taped and left inside on top of the circuits and between that and the top of the case a little dangerous to say the least .

The wirering under the red tape looks new to me as well .

So once again others have tinkered with the design a little .

I suppose all those caps need replaceing look dry and cracked ,well this is mine i will show a cleaner verson next post sort of helps seeing a good one.
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that little red push button on the bottom does not look original and looking at other scopes its a connector
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what the hell !
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This does not look original either
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Last edited by Harry Dalek on Sun May 10, 2015 5:01 pm, edited 2 times in total.
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Philips GM5655 V2

Postby Harry Dalek » Sat May 09, 2015 9:49 pm

Heres what a cleaner one looks like.
https://www.youtube.com/watch?v=7ylUWCa6Ew8

this one is the same year as mine
http://www.greentrace.co.uk/oscilloscop ... gm5655.php

looks like he has replaced near on all the parts
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Philips GM5655 V2

Postby Steve Anderson » Sun May 10, 2015 2:46 pm

This isn't going to be as easy as the previous 'scope fix due to it's age and the very tight space that everything is crammed into...it is some 56 years old!

I have downloaded the manuals/circuits but I haven't yet looked at them. I note you've already powered it up, you were lucky that nothing went 'bang' or no clouds of smoke. For the while don't power it up again, let me go though the circuits etc...

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Re: Philips GM5655 V2

Postby Steve Anderson » Sun May 10, 2015 3:19 pm

Just to confirm the model No., is the nameplate on the back of the case the same as below? The serial number of course will be different, but hopefully it's a GM5655/02.

What valves/tubes are fitted? This will help date it and find the correct manual for it. The manuals you posted cover three different models.

You're correct, that push-button wouldn't have been there originally but an input connector.

You'll note that in the video there's a horizontal burn across the tube, it must have been left on for a long time with no input signal. Thankfully you can still get the DG7-32 and they're not that expensive, well, as far as CRTs go. The last two I bought about 10 years ago were GBP 25.00 each.

Steve A.
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Re: Philips GM5655 V2

Postby Harry Dalek » Sun May 10, 2015 5:16 pm

Steve Anderson wrote:This isn't going to be as easy as the previous 'scope fix due to it's age and the very tight space that everything is crammed into...it is some 56 years old!

I have downloaded the manuals/circuits but I haven't yet looked at them. I note you've already powered it up, you were lucky that nothing went 'bang' or no clouds of smoke. For the while don't power it up again, let me go though the circuits etc...

Steve A.


I noticed when adjusting one of the pots a spark jumped across one ! i wasn't to worried about the bang and smoke as i powered it up a few times over the years but never till now have i looked inside ,i think i would of been more worried had i known about the floating power supply pot !

Really to do it right would be to pull it to bits and start again but the point to point wireing is a hard one to get your head around being all over the place ,i think the resistors would be fine and valves ,there are one or 2 parts i havce not idea what they are early diode or cap of some sort .

I need a game plan here to tackle a correct appoach to fixing it ...i suppose looking at where the add on floating pot is connect to might be a good start .
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Philips GM5655 V2

Postby Harry Dalek » Sun May 10, 2015 5:57 pm

Steve Anderson wrote:Just to confirm the model No., is the nameplate on the back of the case the same as below? The serial number of course will be different, but hopefully it's a GM5655/02.


I just took a photo of mine yes its a 02 i think i read its a 1959 model if its a 02 but have also seen 1955 ? sounds about right a 50's model .

What valves/tubes are fitted? This will help date it and find the correct manual for it. The manuals you posted cover three different models.


OH okay i had a look
2 6v4 power supply rectifiers little plate next to it says Ez80
2 12At7 Ecc81
2 very hard to read i think 6bv8 EF80
1 6AJ8 ECH81

I hadn't looked into any difference in models my self ,some of the schematics are poor .


You're correct, that push-button wouldn't have been there originally but an input connector.



It doesn't seem to do any thing not sure the reason sounds like i need to replace that with a plug again in time .

You'll note that in the video there's a horizontal burn across the tube, it must have been left on for a long time with no input signal. Thankfully you can still get the DG7-32 and they're not that expensive, well, as far as CRTs go. The last two I bought about 10 years ago were GBP 25.00 each.

Steve A.
[/quote]

I think mine has this burn as well ! i can live with that you don't put people down if they have grey hair :wink: it shows character ! it must of had a hard working life ...there also must of been many of these made and a popluar model, would of been a great hobby scope due to its size for the times .

Thanks for looking at this one with me steve ,i'll see also if i can track any thing else down onit .
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Philips GM5655 V2

Postby Steve Anderson » Sun May 10, 2015 7:38 pm

OK, armed with that new data the most applicable manual is your upload GM5655_4.pdf. I have no problem with the diagrams, they're not pin-sharp but quite legible.

The valve/tube compliment should be/is from what you've posted:-

2 x ECC81/12AT7 (a slight typo there Harry) Dual Triode.
2 x EF80/6BX6 (hard to read so an 'X' looks like a 'V') RF Pentode
1 x ECH81/6AJ8 Triode-Heptode
2 x EZ80/6V4 Full-wave rectifiers

The European and US equivalents are exactly the same above. All of these are still easy to get these days should it be necessary.

Let me think about where to go and what to do next...

This will make a very useful NBTV display where you can check out other circuits/cameras/whatever without having to tend to a mechanical device. Once whatever you're working on is OK replace this with a genuine mechanical device. The screen is clear, no graticule and at 3" diameter large enough for 32 lines. But it's useless for SSTV due to the phosphor type. The only other thing that would need be to added is some form of grid modulation, but that's down the road for now...

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Re: Philips GM5655 V2

Postby Harry Dalek » Sun May 10, 2015 8:19 pm

Steve Anderson wrote:OK, armed with that new data the most applicable manual is your upload GM5655_4.pdf. I have no problem with the diagrams, they're not pin-sharp but quite legible.


I was just looking at that one my self the others are hard make out for me but this one the valves look all the same and the manual is ok least it has a parts list .

The valve/tube compliment should be/is from what you've posted:-

2 x ECC81/12AT7 (a slight typo there Harry) Dual Triode.
2 x EF80/6BX6 (hard to read so an 'X' looks like a 'V') RF Pentode
1 x ECH81/6AJ8 Triode-Heptode
2 x EZ80/6V4 Full-wave rectifiers


Yes bad eyes and half rubbed off numbers letters bit of a guess i was happy they had insight to put little metal similar tube numbers next to the tubes.

The European and US equivalents are exactly the same above. All of these are still easy to get these days should it be necessary.


I have a fair few tubes i collected over the years so i think i would have a spare if something gos all the tubes light up in the scope but .

Let me think about where to go and what to do next...


I found this some one repairing one of these worth a look .
https://translate.google.com/translate? ... edit-text=

I think he found most of those large black caps needed to go .

This will make a very useful NBTV display where you can check out other circuits/cameras/whatever without having to tend to a mechanical device. Once whatever you're working on is OK replace this with a genuine mechanical device. The screen is clear, no graticule and at 3" diameter large enough for 32 lines. But it's useless for SSTV due to the phosphor type. The only other thing that would need be to added is some form of grid modulation, but that's down the road for now...

Steve A.
[/quote]

I was wondering if it was any good for NBTV monitor one day i was always thinking of converting it but i don't like the idea of pulling it to bits if the scope could do that anyway as is but never got arond to to looking at it till now ...it has a few plug in inputs i was never sure about had no manual till now ,i think i can pdf convert to english with out pictures least then i can read it .
So doesn't sound impossiible to repair but i know it needs to be a cautious repair .
Yes pity about no lag in the display for old sstv but with that screen burn it sounds like it has a mighty amount of scanning light may be good for flying spot perhaps ...depends on how fine a raster line focus wise it can do as well.
The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Philips GM5655 V2

Postby Steve Anderson » Mon May 11, 2015 2:31 pm

It seems that there's going to be quite a bit to do on this. My plan of attack would be simply getting the thing to work first, then remove the modifications performed by someone else. If possible trace out and draw the mods. and have a guess as to why they were done. If the thing performs as it should with the mods removed and put back to original then all is well.

This is an oscilloscope, but compared to later models it's not completely useless but nothing is calibrated and there is no graticule so you can't measure voltages or time/frequency only observe waveshapes - you can have a very rough guess at volts/time though. So with that it would make a good NBTV display, but some gentle modifications would be required.

The internal timebase will run at the NBTV 12.5Hz frame rate but this would require a swap of the deflection plates to get it to go right-to-left - a minor mod.

You would then need to make an external timebase of 400Hz to feed into the vertical channel (easy).

The biggest mod is actually an addition so putting the instrument back to original would be easy. This is for the grid modulation arrangement which would be quite simple using an opto-isolator and a few other parts.

Now as far as SSTV goes you would need to replace the DG7-32 CRT with a DP7-32 which has a P7-like phosphor, and although they were made they are very rare, and I mean very rare... = very expensive if you can find one. The vertical channel would need extensive work to be able to provide the 8-second vertical scan. So I wouldn't even contemplate any of this.

The link you provided has sound advice and I suggest you follow this guys method and gradually weed out all the duff components.

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Re: Philips GM5655 V2

Postby Harry Dalek » Mon May 11, 2015 6:44 pm

Steve Anderson wrote:It seems that there's going to be quite a bit to do on this.


Yes Steve its not something you can rush either .

My plan of attack would be simply getting the thing to work first, then remove the modifications performed by someone else.


I think its logical to say the power supply transformer works i have heaters lighting up and high voltages ...and no bang or blue smoke on power up and an indication on the crt its ok and has voltages going to it .
The modifications i wish they hadn't but i will have to deal with it .

If possible trace out and draw the mods. and have a guess as to why they were done. If the thing performs as it should with the mods removed and put back to original then all is well.


The big one that worries me is the floating pot which might be connected around the high voltage power supply so i am guessing perhaps some high voltage control wanted for some reason ,but yes i will see and draw where it gos ,i had a quick look the 2 red wirers either side of the pot look to be connected in picture below near the silver power caps ,need to see with my multi meter for sure and can't tell till then where the middle grey wire from the pot gos ,just need a bit of time to work onit .

The front panel control inputs less of a worry but again yep i need to see why the hell someone wanted to change it .

This is an oscilloscope, but compared to later models it's not completely useless but nothing is calibrated and there is no graticule so you can't measure voltages or time/frequency only observe waveshapes - you can have a very rough guess at volts/time though. So with that it would make a good NBTV display, but some gentle modifications would be required.


Oh it does have a visor and a plastic graticule removed at the moment i just replaced it for a picture see again below .perhaps i will just keep it there with blu tack easy to remove for any NBTV experiments .


The internal timebase will run at the NBTV 12.5Hz frame rate but this would require a swap of the deflection plates to get it to go right-to-left - a minor mod.


Could it be inverted before hand in circuit any case thats good to know .

You would then need to make an external timebase of 400Hz to feed into the vertical channel (easy).


I have done that in the past a good 10 years ago for my Trio scope

The biggest mod is actually an addition so putting the instrument back to original would be easy. This is for the grid modulation arrangement which would be quite simple using an opto-isolator and a few other parts.


OH thats interesting ..i will have my revenge for some other owner in the future ! any thing that really makes it work better why not i say .
It sounds like i will have to replace a the tar caps they would be shot so it will not be original and its already been played with ,its only hope at another working life is a repair and replaced parts .

Now as far as SSTV goes you would need to replace the DG7-32 CRT with a DP7-32 which has a P7-like phosphor, and although they were made they are very rare, and I mean very rare... = very expensive if you can find one. The vertical channel would need extensive work to be able to provide the 8-second vertical scan. So I wouldn't even contemplate any of this.


I recall trying a slow scan tv with again my trio scope you could see a few lines sort of work out a picture at 8 sec scan but i will be happy with nbtv use.

The link you provided has sound advice and I suggest you follow this guys method and gradually weed out all the duff components.

Steve A.
[/quote]

Thats good i have been studying the repair ,i just wanted to run it by you ....sounds like i will have to pull a circuit panel out as 2 tar caps are between middle of the scope and hard to get to .
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Philips GM5655 V2

Postby Steve Anderson » Mon May 11, 2015 11:08 pm

It seems that the graticule was for go/no-go testing of some form of device with its central rectangle, we can only guess. Perhaps the mods were somehow tied into this and was a customization for a production line. A rather poorly carried out customization though. At the radar company I used to work for they also sometimes had to customize instruments for production purposes but it was done properly with assistance from the instrument manufacturer. It would appear not so in this case - I can't imagine Philips condoning this sort of bodging.

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Re: Philips GM5655 V2

Postby Harry Dalek » Tue May 12, 2015 7:08 pm

Steve Anderson wrote:It seems that the graticule was for go/no-go testing of some form of device with its central rectangle, we can only guess. Perhaps the mods were somehow tied into this and was a customization for a production line. A rather poorly carried out customization though. At the radar company I used to work for they also sometimes had to customize instruments for production purposes but it was done properly with assistance from the instrument manufacturer. It would appear not so in this case - I can't imagine Philips condoning this sort of bodging.

Steve A.


I just had a look to see if i could find another Gm5655 with this visor and graticule ..i see some with visors and some with a graticule but none really similar to this ,i would of thought the visor was original but it is different to the other google images , perhaps some one just made it as you think....i never really thought about it it looked to me to have been glued in place once ,perhaps the 2 examples here are also home made modifications
With all the other fiddling done to it i would now not be surprised...

As you mentioned i need to get as much dirt dust off it for a start ,i'll take the valves out and put them some where safe ,i would like to get at the 2 tar caps in the center of the scope replaced ,some disassembly needed unfortunately....I know i have to trace the floating pot and since i am going to document this may as well do all this now and not later.
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Philips GM5655 V2

Postby Harry Dalek » Wed May 13, 2015 11:35 am

I took the front panel off today as theres some tar caps that would need replacing and only way to get at them unfortunately is to do this .

I also had a look at the floating pot it seems its just just using the pots built on switch ,i have 2 red and 2 grey wires ,i will leave it for now ,i am starting to think it was power on off switch ...who ever did this never got around to doing any thing apart from putting some electrical tape around it.

I will leave it for now as is and check the switch i was thinking it was a resistance connection until i took the tape off .
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Philips GM5655 V2

Postby Harry Dalek » Sun May 17, 2015 6:16 pm

I worked on the scope today and replaced these 0.1 uf 100nFcaps all 4 were the same small rated 400 large 600volts i didn't have any thing rated at this value at 600 volts apart from 4 .068 68 nF rated at 650 volts so for now i wanted to see if the old caps were bad .

These were the hardest to get to so tackled these first ,after replacing i have a line as you see ,i was hoping for a dot my self :wink: but least its showing something on the screen ...

Theres no way to center the display its set so i suppose in time i am going to have to change parts to adjust it .

Theres no frequencey sweep so i would say most of or all the old Tar capacitors are caput broken :cry:

The rest of the scope is a bit easier now to get at the parts and check so leave that for later in the week .
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now seeing what that red push button switch does
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powering off
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The electromagnetic spectrum has no theoretical limit at either end. If all the mass/energy in the Universe is considered a 'limit', then that would be the only real theoretical limit to the maximum frequency attainable.
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Re: Philips GM5655 V2

Postby Steve Anderson » Mon May 18, 2015 7:44 pm

Well you're getting somewhere here. I simply as a matter of course would replace all those 'tar' capacitors. Even if they seem good now - in 12 months time? While you've got the thing apart you may as well deal with them all in one go. Otherwise it seems to be taking a semblance of life it seems.

At least the CRT appears OK.

100nF/630V caps are easy to find and quite cheap to buy here, I hope they are in Oz.

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