My Spectravideo SV-328 is glitching

Страница 1/3
| 2 | 3

By Matthew Sammut

Resident (48)

Аватар пользователя Matthew Sammut

23-06-2015, 13:08

Hi,

So I've had my trusty SV-328 for a long while now, but it seems that it is not working properly. When it is turned on, it loads fine, and runs smoothly and can be used normally. After a couple of minutes, a bunch of random characters appear on the screen and everything just crashes. When I turn off the SV and turn it on again, random characters still appear on the screen. I have to leave the SV-328 to cool down and discharge for at least 15 minutes before turning it on again for it to work fine for a couple of minutes again.

Are these signs of a faulty capacitor? Please help, and thanks in advance. Smile

Yours,
MathuSum Mut

Для того, чтобы оставить комментарий, необходимо регистрация или !login

By gdx

Enlighted (6071)

Аватар пользователя gdx

23-06-2015, 14:59

Try changing the thermal paste of regulators after cleaning. (Put a thin layer.) Check if there is no bump on the capacitors. Also check the soldering.

By Matthew Sammut

Resident (48)

Аватар пользователя Matthew Sammut

23-06-2015, 16:00

The regulator does not have thermal paste, it is just a blob of regular silicon that came with it. I also installed a small fan inside for cooling. The capacitors do not seem bulged. How do I test the soldering please?

By Wierzbowsky

Guardian (3568)

Аватар пользователя Wierzbowsky

23-06-2015, 17:30

Any of the VRAM chips (4116) getting hot? If yes, they may be causing glitches when they heat up. Try to measure the voltages on pins 1, 8 and 9 of the hottest chips. They should be -5, +12 and +5 respectively. If you have different voltages or some voltage is missing, look what voltage regulators output. One of them may be broken and your chips are being stressed too much.

By Matthew Sammut

Resident (48)

Аватар пользователя Matthew Sammut

23-06-2015, 21:02

Thanks, I will try that. The component that gets hottest though is this one: , but I don't know its function. It's not a VRAM chip though. I'll test the pins and return the results. :)

By Wierzbowsky

Guardian (3568)

Аватар пользователя Wierzbowsky

23-06-2015, 21:26

This is a voltage regulator. It's supposed to be hot as it dissipates heat while lowering the voltage. See this site for locating the necessary components:

http://www.samdal.com/sv328.htm

By Matthew Sammut

Resident (48)

Аватар пользователя Matthew Sammut

23-06-2015, 21:37

Oh ok. I'll buy a multimeter and check the voltage of the VRAM chips then.

By Wierzbowsky

Guardian (3568)

Аватар пользователя Wierzbowsky

23-06-2015, 21:56

Also posting a picture of the screen with "garbage" on it may help some people here to diagnose the problem.

By Matthew Sammut

Resident (48)

Аватар пользователя Matthew Sammut

23-06-2015, 22:04

I'll take a video of the SV when booting it till the garbled characters start to appear, and link it here. Wink

By Matthew Sammut

Resident (48)

Аватар пользователя Matthew Sammut

24-06-2015, 02:02

Here is the link of the video: https://vimeo.com/131592885

By RetroTechie

Paragon (1563)

Аватар пользователя RetroTechie

24-06-2015, 05:31

Notice that vertical banding in the blue background? Doesn't look like photography artefacts as it's not visible in the border, only in the text area.

That banding means power supply (the 5V in this case, I think) is fluctuating as Z80 / ROM / RAM chips etc vary their current draw on various (de)activation events. Which means capacitors meant to smooth that 5V supply, aren't doing their job.

Read: replace those electrolytic capacitors on the board. Preferably all at once. $5~10 in parts, easy to do. Then check that all supply voltages on those 4116 RAM chips are within normal range (as Alexey said).

They're the round cylindrical parts marked C.. on the board, and ..uF / ..V on the part itself. Replace with same value new parts (not scrounged ones from other equipment!), and make sure replacements go in with same polarity. For example buy a complete set of replacement caps, un-solder / solder back in one by one. Looks like there's a few tantalum capacitors in there too. They may still be good but better replace those too as they're 30 yrs. old anyway so it won't hurt. LOL!

Until that's done, no point in continuing diagnostics, as very noisy supply voltages can cause all sorts of weirdness.

Страница 1/3
| 2 | 3