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Commodore 1084S-P1 repair log.


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  • 1 year later...
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Here's an update to my Commodore 1084 repair. Same monitor, different issue. Thought I'd share the repair log on AA too.

 

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During my Hypersports repair I discovered a problem with the display of my Commodore 1084S monitor. Notice blue missing for “3 LONG HORSE” and “7 POLE VAULT”.

 

http://www.jammarcade.net/images/2017/09/image1.jpeg

 

This will be the third time I’ve performed a repair on this old monitor which I’ve had since the early 90s for my Amigas. At first I would suspect the AV7000 Supergun as the culprit. But subsequent tests would prove otherwise.

 

There’s definitely a better picture with composite or svideo from my c64 and Atari 8 bits but there seems to be a problem showing blue on the RGB input even though some blue is there ( turquoise , cyan.. etc ) in other images. Adjusting the blue gun and turning up the contrast just makes the backgrounds in Puzznic more blue. Where blue is supposed to be on the screen, it seems to not be present as though the signal were being cancelled out. With no RGB signal to the monitor at all, it defaults to a blue screen instead of a white one.

 

Apologies for the sync bands

http://www.jammarcade.net/images/2017/09/image1-1.jpg

 

I suspected the neck board transistors, so I pull out the one responsible for blue and tests with my multimeter show it’s fine. I even swap the transistors around to see if the problem moves to the other gun…. but it doesn’t.

 

I found this really good post on eab [ English Amiga Board ] by Loedown

http://eab.abime.net/showthread.php?t=59401&page=2

 

IC502 TDA 3505 pins 12, 13, 14 are RGB in from Euro Connector /SCART, check voltages there to begin with when inputting a perfectly white screen. Then follow the voltages through to transistors TS604 – 606.

 

The schematic shows the analogue inputs go directly from the RGB connector to the Philips TDA3505 IC via some 100nf caps. Pins 12,13 & 14 are the input RGB signals. I measured 4.3v for red and green but 9.1v for blue. That seems a little too high for blue and the schematic indicates 4v for those signals.

 

http://www.jammarcade.net/images/2017/09/Untitled.png

 

I email caius and to cut a long story short, after a few emails back and forth he finally convinces me that the input of the chip for blue has probably failed so I order a lifetime supply of NOS TDA3505s on eBay from atarifreakz and my package arrives a few weeks later.

 

http://www.jammarcade.net/images/2017/09/image1.jpg

 

 

Not wasting any time. I replace the chip and the picture is now perfect! The Taito logo and blue shadow around the Puzznic logo is now visible. Notice the bricks and backgrounds are also showing up right compared with the previous screenshot.

 

 

http://www.jammarcade.net/images/2017/09/image4.jpg

Edited by palindrome
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  • 3 months later...

Hi Lomax,

 

Had any luck with your Monitor?

 

I'm been trying to repair a 1084S-P1 for a friend and have had the same problems. Replaced the HOT, Flyback, checked every capacitor, tested all the large transistors and reflowed many solder pads, yet still have the whine and no LED.

 

The only thing I haven't done is put the power supply on a load. I've just wired up a lamp to give that a shot.

 

Hope between us that we can figure out what this damn problem is.

 

I'm hoping I haven't killed the new HR7533 in the process.

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Nah, but I’ve still got it all sitting in a bucket. I’m no expert, I only know enough about electronics to be dangerous. I can set it up on a work bench and we can start working on them together - tell me how exactly you plan to use the lamp to test the powers supply - I wasn’t sure how to do this.
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Ok so I removed the Flyback an placed a lamp on pins 3 and 11.

 

I tested the new HR7533 and old flyback on pins 7,11, and HV terminal with a multimeter, and a capacitance meter and got no reading. I seems open circuit, and is certainly showing no diode like behavior.

 

I have a monitor with a dodgy power switch, i found when i powered the board up with the lamp it stayed on. But the dodgy switch wasnt latching.

 

I tried to get it to latch switching in it on a few times quickly, then it happened.

 

The voltage impulse seemed to have taken out some components, and it went back to making the decaying sound before I got a chance to measure if the output was at 130V.

 

I think I must have repaired the fault previously, but had already taken out my new flyback beforehand.

 

The voltage impulse seems to take out component 7452, which is the BT151-500R. I had already replaced this before.

 

Replacing this now hasn't fixed the new problem and it's still making a decaying sound.

 

It sounds like these guys monitors:

 

 

 

Hopefully once I find what else is damaged, and get a new power switch and flyback it will work again.

 

At this stage I have just shorted the switch so I'm not creating any more transient pulses.

 

Any clues to what else the impulse may have taken out?

Edited by Clay81
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I have found this information via another forum which seems very helpful to the problem:

 

https://forums.overclockers.com.au/threads/atari-sc1435-monitor-troubleshooting-and-repair.1214637/

 

Besides the Atari SC1435, the Philips 8833-II and CM11342 have the same chassis as the 1084S-P1.

 

As the commodore manual looks like it was scanned by a potato, you will be able to find a better manual from googling: philips_cm11342_cm1162.pdf

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  • 4 months later...

Easier just to replace the switch, there is someone selling them on ebay. It's not an exact match but I got mine to work with minor modification.

 

I just leave the switch in the on position and power it up via the mains to avoid working the switch. Don't want to replace it again.

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