32" Armstrad psu 05ta071b

[teslacap]

Hi there,

recently I became an Armstrad LCT3285 in, with only Power LED on, but else no function at all. On the PSU I saw a bulg 1000uF/25 capacitor and replaced it and also the whole capacitor-set in the neighbourhood. After I got the result, that even the power led was off now and nothing else changed. That's quite motivating! I'm no beginner and repaired many psu's before, but I've no idea what to do now even because it's hard to find a schematics of this psu inside the internet. Can anybody help me, who has experience with this unit?

[truep]

Re: 32" Armstrad psu 05ta071b

Are you sure you got the polarity right on the caps? Also what caps did you use?

[teslacap]

Re: 32" Armstrad psu 05ta071b

Hi,

I have checked the polarity, it is correct and I use capacitors from KMG.

[budm]

Re: 32" Armstrad psu 05ta071b

Pictures of the board? Do you get standby voltage from the standby power supply section? DC voltage (measured right at the two legs) of the main filter cap?

[teslacap]

Re: 32" Armstrad psu 05ta071b

Good morning,

my statement in the beginning wasn't exactly in all items. I found out now that of course the led is red for a few seconds after switching on mainswitch and expires after to stay about a weak glimmer. Quite interesting is the fact that I can see a large sinewave on the oszi, when I put an inducting coil near the transformer on the secondary psu-part. It seems that the switching part is working in basic function. Could be that there is something wrong with the dc- way after this section. Without schematics it's hard to find. I have added a photo.

[vinceroger69]

Re: 32" Armstrad psu 05ta071b

Good morning,

my statement in the beginning wasn't exactly in all items. I found out now that of course the led is red for a few seconds after switching on mainswitch and expires after to stay about a weak glimmer. Quite interesting is the fact that I can see a large sinewave on the oszi, when I put an inducting coil near the transformer on the secondary psu-part. It seems that the switching part is working in basic function. Could be that there is something wrong with the dc- way after this section. Without schematics it's hard to find. I have added a photo.

from another site same psu 05TA071B
26"+ Power supplies (with and without sound output stage).
Firstly, measure the primary side resistance of TR20, it should be approximately 4 ohms on a good working transformer. If it is not 4 ohms, the transformer needs replacing before fitting the repair kit.

The power supply repair kit includes:

F300 - F3.15A - 067420001811
D315 - 12V Zener - 048320605201
D318 - 2.4V Zener - 048100255131
Q300 - BC337-40 - 046247018001
Q302 BC848 marked 1K on back of pcb under IC30
IC21 - FSD200 – 045000000281 (littlediode stock these)
IC30 - ICE1QS01 – 045000003631 (littlediode stock these)
D325 - 1N4007 – 04832142301
C330 1000uF 25V
C322/356 47Uf 50v
C213 33uF 63V
LINK J316 AND J319



This Applies to PSU pcb which do not have the sound output stage built onto the power supply.
ie
05TA071B
C210 1000uF 25V 20% 105°C replace with -> 470uF 35V 20% 105°C
C211 delete.470uF 16volt
L200 20uH 2.5A replace with -> Jumper Wire



OTHER BITS TO CHECK
Q302 etc BC848 screen flashing marked 1K
R418 is marked 333

other notes to check
double diode D404.
Removing this and cold checking revealed one half of the MBR20200 to be s/c.
Q300 (BC547), Q302, (BC848) and zener diodes D318 (2.4volt) and D315 (12volt).

[teslacap]

Re: 32" Armstrad psu 05ta071b

Hallo,

I have checked the items from your list (including replacing and changing work) and discovered no abnormalities. At least up to the test of the two Zener diodes.
There are wrong values . D318 provides 0 volts and D315 I had first measured 10.8 volts. After replacing it was 11.6 volts. Since I have no Z 2.4 here, I'm considering to switch 4 1N4148 in series possibly. I could , if necessary, adjust the 2,4 volts with a trimmer. This would be only for testing. Should it actually be due to D318 , I'll order a new diode. The term MBR20200 I didn't found. Thank you and until further.