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Faulty Philips PM 5508 Pattern Generator

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by Refugee » Mon Oct 05, 2015 10:44 pm

I would have a good look at the power supply before going any further as the video looks like it has got ripple on it.

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by marc » Mon Oct 05, 2015 10:49 pm

Refugee wrote:I would have a good look at the power supply before going any further as the video looks like it has got ripple on it.

Hi Simon,

When used with 'video out' all patterns work and are rock steady so if the PSU was playing up wouldn't I get issues on both RF and video out ? :aaq

Marc.

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by Refugee » Mon Oct 05, 2015 11:07 pm

The RF part of the unit may well be on a different output from the power supply.
The power to the logic sections is clearly all right though.

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by marc » Mon Oct 05, 2015 11:17 pm

Refugee wrote:The RF part of the unit may well be on a different output from the power supply.

It has a single output PSU of +6v 0 -6v supplying all boards so I guess that means the PSU is unlikely to be at fault (famous last words) :qq1

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by Refugee » Mon Oct 05, 2015 11:36 pm

marc wrote:
TVJON74 wrote:Hi Marc,
Are the dial bulb working OK? The UHF side should be lit when a UHF pre set is being used and the VHF side should be lit when a VHF pre set is being used. The +6V supply is switched between the UHF & VHF modulators and the corresponding dial bulb.
Check the +/-6V supplies are getting to the modulators.

Hi Jon,
Yes the bulb and modulator supply is switching correctly between the two.
However there is only +4.2v and -5.97v at the UHF modulator
VHF modulator is +5.69v and -5.97v

Marc.


This post is the one that is making me suspect the power supply.
That +4.2 volts is a red warning to me being almost 30% down on the 6V it should be.
Surely that is enough for a full power supply examination.
It could be bad switching or decoupling.

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by marc » Mon Oct 05, 2015 11:45 pm

Refugee wrote:
This post is the one that is making me suspect the power supply.
That +4.2 volts is a red warning to me being almost 30% down on the 6V it should be.
Surely that is enough for a full power supply examination.
It could be bad switching or decoupling.

Yep that's bugging me too.
The drop only occurs when the UHF mod is switched into play, when the VHF mod is on the voltages come back up so I reckon it's time to crack open the UHF mod :aaq

Marc.

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by TVJON74 » Mon Oct 05, 2015 11:49 pm

Refugee wrote:
marc wrote:
TVJON74 wrote:Hi Marc,
Are the dial bulb working OK? The UHF side should be lit when a UHF pre set is being used and the VHF side should be lit when a VHF pre set is being used. The +6V supply is switched between the UHF & VHF modulators and the corresponding dial bulb.
Check the +/-6V supplies are getting to the modulators.

Hi Jon,
Yes the bulb and modulator supply is switching correctly between the two.
However there is only +4.2v and -5.97v at the UHF modulator
VHF modulator is +5.69v and -5.97v

Marc.


This post is the one that is making me suspect the power supply.
That +4.2 volts is a red warning to me being almost 30% down on the 6V it should be.
Surely that is enough for a full power supply examination.
It could be bad switching or decoupling.

There is a series inductor and a cap to ground on the +&- 6v rails feeding the modulators. Those supplies are used for both VHF & UHF. Only the +ve rail is switched.

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by marc » Tue Oct 06, 2015 12:00 am

Hi all,

the voltage drop when the UHF mod is switched in was caused by it's panel bulb, once removed the voltage is back up to 5.97 from 4.2
I can now see a very grainy chequer board on UHF 625 but still a way to go.

Marc.
DSCF3437 forum.jpg
At last something on 625 UHF

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by Cathovisor » Tue Oct 06, 2015 12:08 am

marc wrote:Hi all,

the voltage drop when the UHF mod is switched in was caused by it's panel bulb, once removed the voltage is back up to 5.97 from 4.2

Errrr... shouldn't those power supplies be regulated? :aab

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by Refugee » Tue Oct 06, 2015 12:14 am

Can you tack in a modulator from an old video recorder to see if that fixes it?

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by marc » Tue Oct 06, 2015 12:23 am

Hi all,

As if by magic.....
DSCF3439 forum.jpg
UHF 625

DSCF3443 forum.jpg
Even cross hatch works


Don't ask me how but up it's come. :aab
All I have done is remove the UHF panel bulb.
Next thing is try it on a colour set to see if the rest works.

Marc.

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by marc » Tue Oct 06, 2015 1:41 pm

Hi all,

After trying the generator on a colour set it's fairly obvious that the out going RF signal is pretty weak. All patterns and colours are there but quite snowy.
Another look at the internal coax's is on the cards I think.

Marc.

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by Refugee » Tue Oct 06, 2015 1:54 pm

It may be worth having a look at the output transistor in the modulator.
If it is faulty it would account for the modulator dragging the voltage down.

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by marc » Tue Oct 06, 2015 2:27 pm

Refugee wrote:It may be worth having a look at the output transistor in the modulator.
If it is faulty it would account for the modulator dragging the voltage down.

Hi Simon,

I'll do that but as for voltage's there fine since the UHF modulator scale bulb (wrong type) was removed.

Marc.

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by Refugee » Tue Oct 06, 2015 2:53 pm

Have you tried swapping the bulbs over?

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by Alistair D » Tue Oct 06, 2015 3:09 pm

Have you tried scanning the TV across the whole band just in case you are tuned to a spurious output?

Al

 
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Re: Faulty Philips PM 5508 Pattern Generator

Post by marc » Tue Oct 06, 2015 3:28 pm

Hi Simon,

Yep I've tried bulb swapping and the voltage drop moves with the duff bulb to which ever modulator it's connected to so has now been removed and the good bulb is on the UHF modulator.

Hi Al,

I've swept the entire band on both the generator and TV but the signal from the generator remains weak at all points.

Marc.

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