Problem in MSX2 HB-F5 no video signal!

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By Dhampird

Hero (589)

Аватар пользователя Dhampird

19-09-2010, 19:54

Hello, the other day I began to follow tracks with the polimeter on the motherboard HB-F5 to know where some signals going, i remove some ic´s from its sockets to better view about the tracks,I have not done any modification important, only i change the eproms with MSX2+ update and when i tried works perfect, for the moment i didnt change the vdp, only the roms.

The other day I noticed something strange (had not yet changed roms) when i turned on the msx after a minute the screen turns off, and the msx is on. This happen as 2 times, today when i turn on the msx, nothing show in screen, seems that dont boot propertly, the msx power led is on but the CAP key and KANJI key dont turn on if i press it.

Seems like a video (composite signal) or power problem, i´m using a 220V-100V external transformer (100V-58W) with this japanese MSX (100V-26W), i used the tester to ckeck mainboard voltages and seems correct, now i´m checking if any resistor near video signals are bad.

Also remember when i tried a SCART Euro cable i didnt see any on screen, the i read some about The Japanese RGB 21 that this msx use, i hope not worn something using the SCART PAL, after that i built a RGB SCART 21 cable and neither works, seems like some video problem.

Could you help me with some guidelines?

Thanks a lot.
Regards.

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By Manuel

Ascended (19273)

Аватар пользователя Manuel

19-09-2010, 20:11

If caps stops working, it's not a *simple* video problem...

By Dhampird

Hero (589)

Аватар пользователя Dhampird

19-09-2010, 23:23

I checked Resistors and Diodes for now, and seems there is none break. Also i checked it in the mini AC pcb.

Here is the voltages i get from conector power supply that conect in msx motherboard.

img543.imageshack.us/img543/2698/transformer.jpg

By RetroTechie

Paragon (1563)

Аватар пользователя RetroTechie

20-09-2010, 00:36

Check voltages on supply pins of some IC's, or cartridge slot pins - be careful not to make any short circuits while putting those test pins in! Btw: you didn't remove any cooling plates (and then power up), did you? Cool

By Dhampird

Hero (589)

Аватар пользователя Dhampird

20-09-2010, 03:55

I test the voltage in some important IC´s, i get only 2V in Z80, YM2149F, CX23044, CX23045, D8255AC-5, VDP.

In eproms i get 1V.

In Cartidge Slots i get 2V in pins 45 (5V line) and 12,60V in pins 48 (12V line).

About the cooling plate, yes, i remebered remove one time the rectangular plate in component side and then power up, not for much time like 2 minutes when i tried eproms. I´m worried about this only 2V that going to the IC´s, probably this low voltage could break also the IC´s, i´m wonder what ac components could be affected by dont install the cool plate...

Thanks.

By Dhampird

Hero (589)

Аватар пользователя Dhampird

20-09-2010, 04:20

I´m wondering if the problem could be in the component that is catching by cooling plate using also a rubber cap, this probably was heated over not having the faceplate positioned. The component is Low Dropout Voltage Dropper Type, 3 terminal, label like:

3052V
.561

I checked it, and i get:

IN: 12,34V
OUT: 2.5V

By RetroTechie

Paragon (1563)

Аватар пользователя RetroTechie

20-09-2010, 13:16

Eproms should have same reading as everything else since they're tied to same Vcc supply... Question Anyway: if situation is same with cooling plate back on then it's clear the +5V regulator is fried... Crying You're 2nd person to do that in a short while & it's a silly mistake - nothing personal, but people should learn to not f**k with their machines if they don't know what they're doing. Crazy

To replace: you need a fixed output, +5V regulator (preferably low drop type so that input <7V is okay) that can handle at least 2A continuous - I'd choose a 3A type, or 5A one if that happens to be available similar price or cheaper.

See this thread for some suggestions: LT1084CP-5 is an excellent replacement (low drop & pin-compatible with 3052), 78T05 or LM323 (not pin-compatible, not low drop) are other options. Local electronics shop or webshops may have more but you'll have to ask/search around. If you know where you might buy: post link(s) here so that others can check that shop's catalog? Btw: don't loose that rubber isolation thingie - you may need it later!

By Dhampird

Hero (589)

Аватар пользователя Dhampird

20-09-2010, 22:06

Thanks a lot Retrotechie for the help and the explanation, i found in online shop the LT1084CP-5, probably arrived in 2-3 days, i could buy this in:

es.farnell.com/linear-technology/lt1084cp5-pbf/reg-de-tension-ldo-5-0-v-1084-to/dp/1136609

Regards.

By RetroTechie

Paragon (1563)

Аватар пользователя RetroTechie

20-09-2010, 23:51

Yes that's the one, but I'm not sure about minimum orders for Farnell. It might be cheaper/easier to try local shop(s?) first...

By Dhampird

Hero (589)

Аватар пользователя Dhampird

21-09-2010, 01:24

I called 5 most important electronics shops in my city asking about the LT1084CP-5 and noneone had the part. When the part arrives I will tell you whether everything has been solved or not. Hope that if...

By RetroTechie

Paragon (1563)

Аватар пользователя RetroTechie

21-09-2010, 02:18

I meant: check local shops for any fixed +5V, 2A or more regulator. Like above types, but there's many more. Even with adjustable output voltage, which you could use too if necessary. If there's 5 electronics shops in your city, you can be 100% sure they have something you could use.

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