2 Belkin KVM switches have dim VGA output

[MrCreosote]

When compared to a direct VGA connection, these 2 switches both output a darker image. The switches are:

4-port Omniview Pro2 f1dz104t
8-port Omniview either f1da108t OR f1dz108t (look and function same, OSD may be only difference.)

The 4 is dimmer, the 8 is massively dimmer - both with same AC adapter and cabling.

AD ADAPTER:

There were issues with previous AC adapter, it failed during lightning strike that blew up TV and other stuff and tripped a 15 amp breaker in the main panel which also had a whole house Cutler Hammer surge protector.

The symptoms of this failed adapter were massively bad VGA image, flashing, streaking on low portion of image, and other types of distortion resulting in a totally garbage image. The buttons and lights and switching seemed to work. And it did produce a full image on the monitor - it was just garbage.

Replacing adapter produced a good image albeit a dimmer one.

Neither adapter was an original Belkin, both were 12v 1a as required.

8-Port KVM:

This was tried, everything worked, but massively dimmer image.

SPECULATION:

Adapter?
previous produced image problems, perhaps current one also.
the 8 may pull down the weak adapter more than the 4 resulting in dimmer?
(I have a 12v 2a I will be trying)

Capacitors?
I've seen same model monitors both fail exactly the same due to bad caps.
Could apply to these 2 KVMs especially since so old.

Any history of old VGA PS2 Belkin KVMs with bad caps?

Thoughts?
Tom

[stj]

Re: 2 Belkin KVM switches have dim VGA output

pcb pictures?

[momaka]

Re: 2 Belkin KVM switches have dim VGA output

If the new adapters are cheapo no-name garbage from eBay / Amazon / Ali or some similar place, they might not really be capable of 1A @ 12V or too noisy. Try a known good 12V adapter with a higher current capability and see if anything changes.

PCB pictures of the switches would also be good to have, as stj suggested.

[MrCreosote]

Re: 2 Belkin KVM switches have dim VGA output

Will try 2a adapter in next 24 hrs hopefully.

[MrCreosote]

Re: 2 Belkin KVM switches have dim VGA output

Tried another adapter 12v 2a (instead of 1a specified) - NO CHANGE.

Here are pics of the boards:

[MrCreosote]

Re: 2 Belkin KVM switches have dim VGA output

Anyone have a chance to look at the PCB's?

[momaka]

Re: 2 Belkin KVM switches have dim VGA output

I took a look yesterday, but couldn't think of anything much.

For starters, perhaps check or replace the two Canicon caps near the L7805 regulator (U1). While technically linear regulators like 7805 are quite stable and don't need a whole lot of capacitance to regulate properly, Canicon are also some of the worst electrolytic capacitors IME. So try checking / replacing those first. If replacing, you don't need any low ESR caps for these, since 7805 is a linear regulator. Any 85C or 105C electrolytic should do, provided it has OK ESR.

Apart from that, I'm not sure what else to suggest. I'm no expert either, though, so perhaps someone else may suggest what else to try.

[CapLeaker]

Re: 2 Belkin KVM switches have dim VGA output

Corrosion inside the VGA a port? That 7805 regulator… is it getting hot? Check the output voltage on it with with all the jazz hooked up to the KVM.

If there is no amplifier inside the KVM, just multiple splitters. That analog signal is let’s say getting spit once, the loss is 3db loss per split. Now using an 8 port just with splitters… no wonder the VGA signal is dim. 3db’s cuts your power in half.

However I am not sure if these KVM’s have a vga signal booster built in. If they do, maybe there is at least one that’s effed up.

[MrCreosote]

Re: 2 Belkin KVM switches have dim VGA output

UPDATE:

I found a repair of what appears to be the identical 8-port KVM where they had VGA issues: strong horizontal streaking (mine has some when there is sharp transitions from black to white on a scan line, but not dramatic at all).

He added a blue cap on the PCB where there was a place for one and solved his problem.

Mine has that cap!

Here's the link: https://www.instructables.com/Fixing...2-KVM/#discuss

I need to check that "blue" cap in mine. What is interesting is that the cap in question is a small form factor, probably a high density package which is the type of caps that fail. These caps are small enough that the bending stiffness of the aluminum plate is great due to the small diameter and will not bulge as the cap fails.

So this is a prime candidate for a replacement - especially since they are apparently "unimpressive" Canicon caps.

With this discovery, I'm motivated now to check that cap in mine. (or replace if I have one)

[momaka]

Re: 2 Belkin KVM switches have dim VGA output

UPDATE:

I found a repair of what appears to be the identical 8-port KVM where they had VGA issues: strong horizontal streaking (mine has some when there is sharp transitions from black to white on a scan line, but not dramatic at all).

He added a blue cap on the PCB where there was a place for one and solved his problem.

Mine has that cap!

Here's the link: https://www.instructables.com/Fixing...2-KVM/#discuss

I need to check that "blue" cap in mine. What is interesting is that the cap in question is a small form factor, probably a high density package which is the type of caps that fail. These caps are small enough that the bending stiffness of the aluminum plate is great due to the small diameter and will not bulge as the cap fails.

So this is a prime candidate for a replacement - especially since they are apparently "unimpressive" Canicon caps.

With this discovery, I'm motivated now to check that cap in mine. (or replace if I have one)

I just had a look through that Instructibles tutorial.
KVM switch is different from yours... and issue with white horizontal streak lines also appears to be different from yours (dim signal.) In the case of the instructible, it appears that when the person added a cap in an unpopulated spot, that fixed the issue, which suggests the other electrolytic caps might have failed. So it's not really of a fix and more of a band-aid. But it does prove the concept that bad caps can cause issues.

In the case of your KVM, just replace C2, C5, and C28. Then lets see if the dim image persists.