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Sugarland

800 power supply caps replace

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Hi.

 

I bought my first 800 recently and one of its caps on the power supply is bulging a little. The voltages tested OK but I'm not confident in these antique capacitors. I found this post which talked about caps expiring and optimum storage conditions, etc.. This 800 sat unused for 25 years afaik. I would like to replace its caps. Is there a parts list of caps the 800 uses, please? I've searched to no avail.

 

This 800 had a bad pokey that I had to replace and I'm concerned that if the caps are bad it could break this replacement pokey.

Edited by Sugarland

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The Atari 800 Field Service Manual (can be gotten @ Atarimania) has the parts list but it's not in order such that you could ID the PSU parts easily.

 

The Jerzy Sobola schematics has the 800 PSU.

I don't have Sam's computer Facts for the 800 but it likely has schematic and parts list.

 

My advice would be to cross reference physically with your PSU and the schematic as to what parts you need.

 

800 schematic here 800.zip

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I found that schematic unreadable. I'm not an EE. However I did find a site that sells 800 cap kits here https://console5.com/store/atari-800-computer-cap-kit.htmlHave any of you worked with them? Their facebook reviews seem good.

 

Here are the caps in that kit:

Power Supply, REV B			C202	470uF	16vC201	470uF	16vC211	10uF	16vC210	10uF	16vC204	2200uF	16vC205	2200uF	16vC207	4700uF	25vC208	4700uF	25v			Main PCBC179	10uF	16vC199	10uF	16v

I think this does not include what appears to be 'green drop' caps that I can see on the power board. Photo attached of one. Maybe the greens aren't of concern.

post-49049-0-06257700-1525316035_thumb.jpg

Edited by Sugarland
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I think this does not include what appears to be 'green drop' caps that I can see on the power board. Photo attached of one. Maybe the greens aren't of concern.

 

This is a ceramic capacitor. At normal circumstances you don´t need to change ceramic caps. Most times they´re working fine or simply cause a short-circuit :-D

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This is a ceramic capacitor. At normal circumstances you don´t need to change ceramic caps. Most times they´re working fine or simply cause a short-circuit :-D

That's C203 which, according to the parts list in the back of the Field Service Manual, is a 0.22uF(100V) poly film capacitor.

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That's C203 which, according to the parts list in the back of the Field Service Manual, is a 0.22uF(100V) poly film capacitor.

 

Thanks for correction :) - but my statement is also valid for these type of caps. When charged at the typical 5 or 12 volt low-voltages found in the computer of the 80s the aging effect on poly film, ceramic, MKS/MKP etc.pp. capacitors are extreme small.

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Good to know thank you!

 

In this video, Jan Beta replaces DC to DC voltage regulators in a C64. He said that they 'might fail'. I'm wondering if this more applies to the low quality c64 build (lol?) or if it applies to the 800/1200XL since they both have them as one is shown in the previous photo. Looks like the above is a 78M12CT which Jan mentions the 7812 in the C64. Modern ones don't generate nearly so much heat or use so much power according to Jan.

 

I need to do more research but for now I'm guessing the ones in the 800 are of a better quality brand. I can see the M for Motorolla in the 800 but not on Jan's 64. For now I'm not touching them. Guessing it's best to leave it alone for now but one day....

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Good to know thank you!

 

In this video, Jan Beta replaces DC to DC voltage regulators in a C64. He said that they 'might fail'. I'm wondering if this more applies to the low quality c64 build (lol?) or if it applies to the 800/1200XL since they both have them as one is shown in the previous photo. Looks like the above is a 78M12CT which Jan mentions the 7812 in the C64. Modern ones don't generate nearly so much heat or use so much power according to Jan.

 

I need to do more research but for now I'm guessing the ones in the 800 are of a better quality brand. I can see the M for Motorolla in the 800 but not on Jan's 64. For now I'm not touching them. Guessing it's best to leave it alone for now but one day....

Replacing those old inefficient 78xx linear regulators has been something a lot of people have been doing in recent years. I've been replacing the 7805s in the ZX Spectrums with a Tracopower TSR 1-2450 for a couple of years now, much more efficient and no more heat generated so the heatsink is then no longer required and the ULA has more of a chance of surviving for longer.

Edited by Tezz
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ULA?

 

I got some of those new switching regulators with the intent to try them in a 1050, haven't gotten around to it yet.

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Replacing those old inefficient 78xx linear regulators has been something a lot of people have been doing in recent years. I've been replacing the 7805s in the ZX Spectrums with a Tracopower TSR 1-2450 for a couple of years now, much more efficient and no more heat generated so the heatsink is then no longer required and the ULA has more of a chance of surviving for longer.

 

Absolutely right. But when talking about an Atari 400 or 800, it´s more important to replace the 7805 regulator. This one is only specified for 1A max. und typically loaded (Atari 800 with 3x 16 KB RAM cartridges) with approx 800 mA. The 7812 won´t get very warm, but the 7805 gets hot. The TRACO ones are good, but very expensive. Some chinese seller at eBay have step-down converters with 1,5A max. load and something like the LM2576 series on a little small PCB, which has compatible pins for direct replacement of a 7805.

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Absolutely right. But when talking about an Atari 400 or 800, it´s more important to replace the 7805 regulator. This one is only specified for 1A max. und typically loaded (Atari 800 with 3x 16 KB RAM cartridges) with approx 800 mA. The 7812 won´t get very warm, but the 7805 gets hot. The TRACO ones are good, but very expensive. Some chinese seller at eBay have step-down converters with 1,5A max. load and something like the LM2576 series on a little small PCB, which has compatible pins for direct replacement of a 7805.

Indeed, I spoke with someone about those Chinese step-down converters last year, he had personally used them successfully and said they were a nice solution.

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Update!!

 

Last year I replaced the 800's electrolytic caps with a set from console5. They are seemingly of good quality - nichicon. No problems. The 800 worked identically as before after replacing them with the set referenced above in post #5 of this thread.

 

HOWEVER, six months later in February of this year I replaced the original 7805 on the power board with a TSR 1-2450. TRACO Power from Mouser Elec. Now the s-video is very wavy on the same LCD using the same power supply and same video cable. The image is stable but there are lots of darker waves moving through the image in a mostly diagonal way. The only thing that changed is the the new regulator. The Mouser part # is 495-TSR-1-2450.

 

Here is video of the effect:

 

I replaced this 800's extremely yellowed case top half with a new old stock ordered from B&C and my hope is that the new regulator will run cool and not discolor the new case top. Sure it now runs cool with the new 7805 but now the video is poor. Video was very good before.

 

Any ideas as to why this happened? Should I also replace the 7812 or is that not relevant?

 

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Update!!

 

Last year I replaced the 800's electrolytic caps with a set from console5. They are seemingly of good quality - nichicon. No problems. The 800 worked identically as before after replacing them with the set referenced above in post #5 of this thread.

 

HOWEVER, six months later in February of this year I replaced the original 7805 on the power board with a TSR 1-2450. TRACO Power from Mouser Elec. Now the s-video is very wavy on the same LCD using the same power supply and same video cable. The image is stable but there are lots of darker waves moving through the image in a mostly diagonal way. The only thing that changed is the the new regulator. The Mouser part # is 495-TSR-1-2450.

 

Here is video of the effect:

 

I replaced this 800's extremely yellowed case top half with a new old stock ordered from B&C and my hope is that the new regulator will run cool and not discolor the new case top. Sure it now runs cool with the new 7805 but now the video is poor. Video was very good before.

 

Any ideas as to why this happened? Should I also replace the 7812 or is that not relevant?

 

The new regulator is a switching type that is probably generating some ripple/noise. Checking the +5V output with a DMM set to AC volts should give you a reading of how much ripple is present.

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I'm hesitant on installing one inside my 800 for the same reason but since you've already done it you could try adding a choke ( just a hand wound ferrite core with 5 or 6 turns ) and a cap to implement a lc low pass filter.

 

I had the same issue in another power supply I rebuilt but the symptoms were more subtle.

 

Here's a really good video on how to implement one.

 

https://www.youtube.com/watch?v=G-Llhy2ViUY

Edited by shoestring
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Michael (Mytek) has plenty of experience designing A8 systems that use modern voltage regulator type devices like this in place of classic 7805’s and the like. He might be able to offer some suggestions here.

 

Personally I have no problem using original spec 7805’s as replacements in my vintage systems. It’s what they’re spec’d for and I’ve only ever had one of them outright fail on me, and that was in an abused 2600 Vader I bought cheap a couple years back.

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Personally I have no problem using original spec 7805’s as replacements in my vintage systems. It’s what they’re spec’d for and I’ve only ever had one of them outright fail on me, and that was in an abused 2600 Vader I bought cheap a couple years back.

 

The 7805 linear voltage regulator is availible in a 1.5 amp max. version - called 78S05. I´ve also only used this time for replacement all the years and all systems work fine :)

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The 7805 linear voltage regulator is availible in a 1.5 amp max. version - called 78S05. I´ve also only used this time for replacement all the years and all systems work fine :)

 

Good to know. Thank you!! Do they run cool?

Edited by Sugarland

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Good to know. Thank you!! Do they run cool?

 

Not really. Of course the S version will be less hot in the Atari 800 than the standard version, but the difference is maybe 5 degrees C (never checked it for a long using period).

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I suppose it would only be an issue with a lot of upgrades ?

 

I just have the SCCC which I purchased from you and the 800 doesn't draw too much. Though I believe this might change with someone like the Incognito.

 

Just wondering if you still plan to develop the a personality board for the 800? I'll definitely be in line for one...

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Yep, if you're changing the type of regulator, the support circuitry should probably be adjusted for the different characteristics. If the PSU is designed for a 7805, it will have the correct capacitors in place to ensure the output is stable for that type of regulator. Check the datasheets of the other types of regulator to see application notes for what additional circuitry is required and add it (r modify the existing circuitry) - that should eliminate any noise you get from it in the video or audio output. It could be as simple as replacing one capacitor with a different value.

 

Depending on the multimeter, you might not get an accurate reading of ripple, as modules like that typically use switching in the 2- or 3-digit kHz range, which may be beyond the capabilities of the meter to measure.

 

The 78S05 won't be much cooler than a standard 7805 - the amount of energy to dump as heat is the same, and they're in the same package, so it all comes down to the heatsink used. But it won't burn out as easily when it's run close to 1A. There's also a H version that's rated for 5A, but it's in a different package and is intended to be mounted on the heatsink (rather than the heatsink mounted on the chip), so would require some fudging to physically fit it.

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