ST-ranger

May 19

On 5/12/2021 at 6:24 PM, TGB1718 said:

With resistors, if it's rated @2W that's the minimum rating, it's ok to go over i.e. 3W assuming it will still fit

in the PCB, but a0.6W would likely fry itself in a nice mushroom cloud

With capacitors, they are voltage dependant so again if it's 10uF 20V rated, ok to go 10uF 30V, but not 10uF 10V,

there's also tolerances to take into account on both resistors and capacitors.

Great information, thanks again.

Everything is ordered - will post progress! Cheers

May 11

13 hours ago, TGB1718 said:

The DB1 is a W10M full wave bridge rectifier it's rated at 1.5A, so reasonably any mains voltage bridge rectifier

with at least 1.5A rating or above will do the job. MUST BE MAIN VOLTAGE RATED. else smoke ensues

Here's the datasheet.

The SC1384 is an NPN transistor, again, here's the datasheet, seems to be a power transistor with a max

current rating of 1A.

Had a quick look on "FleaBay" and they are still available in the UK, worth checking.

datasheet.pdf 102.08 kB · 3 downloads 2SC1384_UTC.pdf 282.03 kB · 3 downloads

This is fantastic, thank you so much.

I've ordered the SC1384 TO-90L from China - the wait is only a month or so, and they were incredibly cheap.

Sadly I'll have 49 of these leftover, feels like a waste, perhaps time to do the other Ataris while at it.

The W10M, have found a source over here - how do I tell if it's mains rated? Here is the blurb from "fleaBay":

>"The 1.5 Amp Full Wave Bridge Rectifier (W10M) is a single phase Bridge Rectifier. Voltage Range is 50 to 1000 Volts and Current is 1.5 Amperes."

Because my voltage range lies within this (220v to - 240v) is it safe to assume that it is mains rated?

22 hours ago, Chri O. said:

R6 and R7 are 1/2 Watt 0.5W Resistors.

Thank you! All ordered.

-edit- when choosing resistors, is the resistance non-negotiable & the power flexible, similar to capacitors?

I.e. if I need a 51 ohm resistor at 2W, can I choose a 51 ohm resistor at 3W, or perhaps below at 0.6W? Which is better? Thanks.

May 10

4 hours ago, MasterMotorola said:

ST-ranger, take a look at this page... https://www.exxoshost.co.uk/atari/last/psu/index.htm#ASP34

Also, it may be cheaper and better in the long run to replace the entire PSU with a new one made by Mean Well like in this video...

MasterMotorola, thanks for your quick reply, much appreciated.

I've watched the video now, glad to know there is a drop-in replacement.

They are readily available in Australia - can I use these to replace the supply in my 1040STfm and STe? If so, I might do that, and continue to repair the current one.

I have been through the schematics - it looks as if it's in another language to me. Here are the values I've come up with for things that appear damaged:

R5 - 51 ohms 2 W

R4 - 330 ohms 2W

R6 - 3.3K ohms, watts not specified

R7 - 15 ohms, watts not specified

C8 - 1 uF 16v

Is it okay to use any wattage for the above without a W rating?

I might be able to get these from the local electronics supplier.

There are also two components which I'm totally stumped by:

Q1 - ? SC1384

DB1 - No value - another part of the site shows it as a "bridge recitifier". On the original part is has printed on top: "G1 W10M 8741"

Where could I source these components? There are specialty stores I've used for ZX Spectrums, Amigas, etc., however haven't found anything which sells these components for STs.

Thanks again

May 10

'Morning all,

Currently in the process of repairing a poorly 520STfm. This is a UK 520, and it has found itself in sunny Australia, where the voltage is the same (220-240v).

Board is nice and clean, no issues with burst caps or any other visible damage. The main symptom has been no power.

I am replacing the PSU caps based on the Techwiki Astec ASP34 (Mine is ASP34-2).

After removing all of them, I note most of the PSU caps have leaked at some point, so I have cleaned up the bottom & top of the board. Please see the photos.

One of them has explosively decompressed out the side ( C7 ) . A couple of components also look burnt and/or damaged.

Could anyone please assist in identifying the components in the pictures so I can replace them? I have pointed to them the best my limited paint skills allow.