General Stuff(tm)

[stephen_usher]

They are... especially if they're as old as retro-computers.

[exxos]

Drifting next?

[stephen_usher]

[stephen_usher]

Back from RetroFest2025.... Knackered.

Good weekend though the keypad on the Zero 1 master controller became more and more problematic. I'm going to have to try to renovate the carbon impregnated rubber.

[stephen_usher]

Well, the keypad was worse than I thought...

Instead of carbon impregnated rubber it's just a carbon conductive paint. On the "good" pads the resistance is about 1K ohm but on many of the very warn pads it's basically not conductive at all.

IMG_4438.jpeg (216.12 KiB) Viewed 80 times

Anyway, I've ordered some keypad conductive paint off Amazon, which should arrive on Thursday. In the meantime I've designed a replacement keypad PCB which uses 2.5mm high SMD tactile switches just in case the paint doesn't work. I should be able to get the PCBs made, shipped and made up in time for the next show on the 21st June.

Zero-1-keypad.jpg (70.34 KiB) Viewed 80 times

The resistors are there to give an equivalent resistance to the carbon paint.

[stephen_usher]

Well, today's "fix it" episode comes to you from a Denon tape deck which mysteriously stopped being able play audio.

I took it apart and couldn't find anything specifically wrong with it at all, it would still just sometimes have just mains hum on both channels.

On the PSU I did find it strange that some of the lines marked +7.5V were -7V. I found that if I unplugged the control/display board then the voltages came back to something similar to the levels marked, so I took the board out. Other than crusty old flux residue all over the solder side of the board I couldn't see anything wrong. Other than the one big surface mount chip there's not much on there other than the display and tactile switches.

Anyway, so as to check the connections to the board I washed it off with IPA. It cleaned up nicely. Some of the solder joints looked sub-optimal but that would have been from new and not a later issue. Anyway, I decided to see if I could run the deck with the board out of the machine at this point. The board was still a little wet from the IPA but it's non-conductive... The deck worked!

I ran the deck like this for a few more minutes and then the sound cut out again. Touching the board and tweaking components made no difference. Then I had a thought... Was it the flux residue that had gone conductive and my initial wash had worked until the IPA evaporated?

Took the board out again and gave it a good wash in IPA and made sure that the chip legs were cleaned... All working!

So, it looks like the flux residue was the issue all along.

[rubber_jonnie]

Well, today's "fix it" episode comes to you from a Denon tape deck which mysteriously stopped being able play audio.

I took it apart and couldn't find anything specifically wrong with it at all, it would still just sometimes have just mains hum on both channels.

On the PSU I did find it strange that some of the lines marked +7.5V were -7V. I found that if I unplugged the control/display board then the voltages came back to something similar to the levels marked, so I took the board out. Other than crusty old flux residue all over the solder side of the board I couldn't see anything wrong. Other than the one big surface mount chip there's not much on there other than the display and tactile switches.

Anyway, so as to check the connections to the board I washed it off with IPA. It cleaned up nicely. Some of the solder joints looked sub-optimal but that would have been from new and not a later issue. Anyway, I decided to see if I could run the deck with the board out of the machine at this point. The board was still a little wet from the IPA but it's non-conductive... The deck worked!

I ran the deck like this for a few more minutes and then the sound cut out again. Touching the board and tweaking components made no difference. Then I had a thought... Was it the flux residue that had gone conductive and my initial wash had worked until the IPA evaporated?

Took the board out again and gave it a good wash in IPA and made sure that the chip legs were cleaned... All working!

So, it looks like the flux residue was the issue all along.

Interesting, that's a new one on me, but definitely a worthwhile exercise on old gear, so much stuff have bad flux residue.

[stephen_usher]

It looks like I brought back more than just memories from Swindon...

The cold I thought I had turns out to be COVID!

I just did a test and two lines.

[exxos]

Oh no Hope it doesn't turn into a epic.

[PhilC]

It looks like I brought back more than just memories from Swindon...

The cold I thought I had turns out to be COVID!

I just did a test and two lines.

Oh that's gotta suck. Hopeyou get over it quickly and easily