Hot VIC

[chysn]

One of my VIC-20s (https://cbmvic.net/registry/503) gets hot. Touching it inside the cartridge port after a half hour is painful.

Along with this heat, the audio becomes strange. The mid channel plays unpredictable frequencies (for example, higher frequency values may sound lower in pitch than higher frequency values, and all frequencies are wrong in some way). When cool, the audio is as expected.

Are there any common root causes of heat? Would heatsinks anywhere be of any value? I've taken this VIC temporarily out of rotation, as I worry that the 6560 is in some danger, although video output does not seem to be affected.

[Mike]

Could you post a photo of the mainboard? I'd guess it's an early 2-prong machine with a single heatsink (the later 2-prongs got a heatsink separated from the expansion port, as people got burns when they handled cartridges ... ).

Are there any common root causes of heat?

All energy transformations ultimately end up in heat.

From experience, the VIC chip in the VIC-20 gets rather hot, around 55..60 °C (or 130..140 °F). Next (in a 2-prong), voltage regulator and rectifier. Then, either BASIC (in program mode, running BASIC programs) or KERNAL ROM (in direct mode), and the character ROM. The CPU, behind all these. Everything else should run rather cool. If the VIAs or any of the RAMs or logic chips become hot so you can't touch these, they're on the brink shorting the supply voltage.

[chysn]

Could you post a photo of the mainboard? I'd guess it's an early 2-prong machine with a single heatsink (the later 2-prongs got a heatsink separated from the expansion port, as people got burns when they handled cartridges ... ).

I don't think this one's particularly early. The chip date codes are consistently in the latter half of 1982.

Are there any common root causes of heat?

All energy transformations ultimately end up in heat.

Touché.

From experience, the VIC chip in the VIC-20 gets rather hot, around 55..60 °C (or 130..140 °F). Next (in a 2-prong), voltage regulator and rectifier. Then, either BASIC (in program mode, running BASIC programs) or KERNAL ROM (in direct mode), and the character ROM. The CPU, behind all these. Everything else should run rather cool. If the VIAs or any of the RAMs or logic chips become hot so you can't touch these, they're on the brink shorting the supply voltage.

Right now, I'm listening for one of the voices to diverge from the others. After 40 minutes, the expansion port heatsink is at 50C, and all the chips are between 30C ~ 33C. The VIC chip remains at 30C.

[chysn]

It's been an hour and I'm unable to reproduce the original problem, of VIC voices going out of tune. Maybe it's because I have the VIC case open to room-temperature air? I'll close it up for a while and see if anything changes. Temperatures are remaining really stable (under 35C) for every component that I can hit with a laser.

[chysn]

Yep... When I have the case closed up, the sound goes out of whack. When I re-open the case, the sound gradually goes back to normal after a couple minutes.

[Mike]

My bet is on either rectifier or voltage regulator. The VIC chip isn't particularly happy if it gets out-of-range supply voltage.

In the best case, the heat paste has dried up over the years, so you could try removing the sinks, removing old and re-applying new heat paste, and see if that improves things. Otherwise, you should replace both without much ado.

[chysn]

My bet is on either rectifier or voltage regulator. The VIC chip isn't particularly happy if it gets out-of-range supply voltage.

In the best case, the heat paste has dried up over the years, so you could try removing the sinks, removing old and re-applying new heat paste, and see if that improves things. Otherwise, you should replace both without much ado.

Thanks! That sounds like a good plan. Wow, those voltage regulators aren't cheap!

[MCes]

The heat inside the old type of board can be drastically reduced by using a DC-DC converter in place of the 5V linear regulator
(I suggest the DC-DC converter type with toroidal core).
The heat inside is also generated by the diode rectifier bridge,
but if the DC-DC converter is used the current on the rectifier will be reduced with benefit also on the heat generated by the rectifier.



The slightest HW modification can be made by applying the converter without unsoldering the old regulator,
the DC-DC converter must be set 0.1V more than the nominal "5V" measured on the board before the mod (it must not be higher than 5.25V).

Another way can be to buy a DC-DC converter with 2 settings: CC (constant current) and CV (constant voltage).
Adjust CC to zero and CV for 5.25V, then solder it in VIC20 without unsoldering the old regulator.
Turn on and increase the CC (counting the turns) until the "5V" line rises to 5.25V, then decrease the DC setting by 20% of the turns.
Now you have the same old voltage on "5V" line but the current to the board is 80% from the DC-DC converter and 20% from the old regulator (which determines the output voltage): the heat generated by the 5V generation decreases by 80 %.

[chysn]

The heat inside the old type of board can be drastically reduced by using a DC-DC converter in place of the 5V linear regulator
(I suggest the DC-DC converter type with toroidal core).

I ordered some of the original voltage regulators, so I might just wind up replacing it. But do you have a link to the appropriate DC-DC converter?

[MCes]

I tried to select the DC-DC converters CC CV but unfortunately all those I have seen on sale are not suitable because to measure the current they interrupt the ground line input-output with a small shunt resistor, while in our case the point of ground is unique in common between input and output.

Normally I try to modify and let it be easy to go back to the original machine, but in this case I think that is better remove the old regulator (and its heatsink) for replacing it with a 5V 5A DC-DC step down converter.

examples of DC-DC converter: 5A max type for a good thermal security margin.


the traditional (toroidal inductor coil magnetically close: self-shielding)
https://www.ebay.it/itm/262670091643?ha ... 1&LH_BIN=1

With active-rectifier middle-high frequency (500 KHz) inductor coil magnetically close (self-shielding)
https://www.ebay.it/itm/402626397567?ha ... E&LH_BIN=1

[chysn]

Thanks! I think I'll try the straight replacement first, and if that doesn't reduce the heat, I'll try something like that.

[doug_in_nc]

Another alternative is using a modern plug-in compatible voltage regulator. I saw this one tested in a VIC on a Chuck Hutchins youtube channel a while back, and the results were impressive. I haven’t verified myself yet, but it’s on my to-do list.

https://www.ezsbc.com/product/psu5-nonoise/

https://youtu.be/w5sTxsx4qgY