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Display module repair (IFR A-8000 Spectrum analyser)

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jimmc101
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I have a faulty display module (COMPUTRON MOD # 115-35 DMK7) in my spectrum analyser (vintage 1987).

I confess I'm not familiar with TVs but to me it looks a bit similar to a monochrome set of that era.

It is a 7" display similar to a TV but with the scan coils turned to give a vertical raster.

(I think that the external connections show the rotated names but parts of the circuit diagram refer configuration before rotation.)

Would anyone like to hazard a guess as to what IC101 is, I would like to get some idea what signals to look for before I dismantle half the unit to get at the display module.

I forgot to mention the fault is total lack of any picture.

Jim

Schematic
 
Posted : 26/03/2020 7:47 pm
jimmc101
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I've done a bit more reading, I was wrong, all Horizontal and Vertical references are to the unrotated  state.

Horizontal sync is a 19.608kHz squarewave, Vertical sync unknown but does not matter as it's shorted out by the modification that replaces C116A by a short.

 
Posted : 26/03/2020 10:36 pm
Nuvistor
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No idea about the chip, hopefully may just be a PSU fault otherwise is multimeter and scope.

 

Frank

 
Posted : 26/03/2020 11:12 pm
jimmc101
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Well I managed to get it apart and found that a lot of corrosive glue had been used to hold large components and cables down.

CRUD

 The ribbon cable connects to the CRT base and the worst corrosion occurred on the G2 conductor at both ends.

Board cleaned and recapped where necessary and ribbon cable connections remade.

I hope to reassemble it all tomorrow.

IC101 remains a mystery, It really annoys me when manufacturers sand off the type markings.

 

Jim

 
Posted : 27/03/2020 8:01 pm
Nuvistor
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Hope that sorts it out, that glue really is corrosive.

Frank

 
Posted : 27/03/2020 8:50 pm
jimmc101
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I'm pleased to say that that the analyser is working now.

It lives

Jim

 

 

 
Posted : 28/03/2020 8:23 pm
Doz, Nuvistor, Red_to_Black and 9 people reacted
turretslug
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Blimey, that's a shocking example of how destructive something apparently innocuous like glue can be. Must have been a considerable relief to have it come back to life.

 
Posted : 28/03/2020 8:59 pm
6.3volts
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@jimmc101

Remarkably fortunate repair. Have you removed any other glue before it wreaks further havoc? I've yet to experience this type of destruction, the only glue I've seen is not turning brown so may be a later type.

 
Posted : 26/05/2020 11:29 am
jimmc101
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Oh Yes! Every component with a hint of glue around it was removed and the board thoroughly scraped clean followed by alcohol wash.

Most components affected were replaced, the rest were treated in the same way as the board.

Fortunately the glue seems to be confined to the display unit (made by Computron and dated August 1987).

Jim

 
Posted : 26/05/2020 9:38 pm
Anonymous
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@jimmc101

Hi Jim,

I used to run into that brown corrosive glue all the time on PCBs on a Gyrocompass from Japan built in the 1980s (TKC).

It tends to get conductive too as it goes from light brown to dark brown. I would have to spend ages picking it off pcbs.

I also have an IFR A-8000 and had to do the same on the CRT display board.

Leon

 
Posted : 01/10/2022 8:11 am
Anonymous
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@jimmc101 In answer to the original questions about IC101, I think it is a AN5435.

My A-8000 has a Computron 115DMX board with the ID ground off IC101 but looking at similar monitors I'd guess that's the wee beastie.

(Jim, thank you for the welcome PM but I'm a newby so I don't have PM privilages yet. I'm sorry, I don't have any service info for the A-8000. I was hoping you might have something beyond the A-7550 Maitanence Manual. I'll let you know if I ever find anything)

Leon

 
Posted : 02/10/2022 11:43 pm
jimmc101
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Sorry no more information than you have. Plenty of sites have the Operators manual but only phishing sites list the service manual.

Jim

 
Posted : 04/10/2022 8:44 pm
vernsr02
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@jimmc101 I'm a new member, so obviously a bit late. IC101 is most likely a AN5415, manufactured by Panasonic around the 70s & 80s. It was only one of a series of Chips for TV, but significantly here it's probably the only one with its pin 10 as the main ground pin as is the case with this monitor. The general pin out suits  the monitor circuit. I hate type number removers and will counter their actions as well as I can.

 

 
Posted : 21/09/2023 1:39 am
vernsr02
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For maybe 30 years I've been working on the IFR A-7550 Spectrum Analyzers with quite some success.  They use the same video unit. I have lots of notes and would be most happy to share them. There are still plenty of problems I haven't seen, but you can give me try if you like.

 
Posted : 21/09/2023 1:50 am
vernsr02
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As soon as I'm permitted I will leave a file or two about these monitors in the hints section.

 
Posted : 22/09/2023 10:39 am
jimmc101
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Touch wood, mine are OK at the moment but I would love any information you have for future reference.

Jim

 
Posted : 22/09/2023 9:58 pm
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