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Old 7th May 2017, 6:55 pm   #1
Apfelmus
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Default Philips PM5518 pattern generator: St35035 display driver

Hi folks,

I hat to put my pattern generator on the workbench as its display was nonworking. Only the display... a four digit, 7-segment LED arrangement.

I hoped for an easy repair, but it turned out this is some kind of integrated vodoo whatever circuit I cannot find anything about.

Since the LEDs on the buttons do work correctly I suspect the fault to be within this driver circuit. I'm still doing some measurements, but it would be helpful to have some more knowledge about that circuit.

For example: what is the voltage supposed to appear at pin7 (brightness control)? In my case its as good as clamped to 5V with no change at all when turning the pot. Bringing down the voltage with an additional resistance towards ground (20k) does not brighten the display...

cheers & thanks already
Martin
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Old 8th May 2017, 11:45 am   #2
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Default Re: Philips PM5518 pattern generator: St35035 display driver

Hello Martin
I posted the operating instructions and service manual for the Philips PM 5518 in 2010, see if the following link works. If not use the search box at the top of the header.
https://www.vintage-radio.net/forum/...t=55775&page=2
There was another member with the same problem as you have with the display and I think he found a way to solve the problem.
Regards Stan.
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Old 8th May 2017, 2:04 pm   #3
Apfelmus
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Default Re: Philips PM5518 pattern generator: St35035 display driver

Many thanks, Stan!

I skipped the thread you gave me based on its subject - I already had operator and service manuals. But it contained the vital information about the "real-world" number of this circuit.

It seems I can find an LTM8328 at my local dealer...

cheers
Martin
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Old 8th May 2017, 4:52 pm   #4
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Default Re: Philips PM5518 pattern generator: St35035 display driver

Hello Martin
I am please the link was of some use to you, even though it was posted some seven years ago.
Regards Stan.
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