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FReHD build. Made my first FREHD but the max232 is burning hot!

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Syndikated

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I built my first frehd from pcbway https://www.pcbway.com/project/shar...ulator_for_the_TRS_80_Computers_f3df36d6.html, It works but the max232 is burning hot. I mean burning! I burnt my finger tip touching it and now have a blister.

If you read notes on the pcbway page he even notes the max232 is super hot! I wish I would have noticed that before I built it. I followed the plans exactly and like I said it works but what can I do to remedy this burning hot max232 IC?
 
Warm is ok, blister means drawing a buttload of power with a short.
Max232 shouldn't be hot in normal operation, after I eat I'll open my external frehd and power it on and see how hot mine gets.

And if was hot enough to burn you, the chip is probably shot.
 
Ok, managed to fine mine, and my max232 is cool as a cucumber.

1. Where did you buy your max232s?

2. Which max232 are you using? MAX232, MAX232A, or MAX232N?

I'm still using my old stock of max232s that I bought in the early 2000s. I'm using a TI MAX232N bought from either digikey or mouser.

The notes on the project page state.

. I went ahead and populated the MAX232's since I had some. When I did the first chips-installed smoke test and checked power, I found that the 5V line was at only about 4.3V. After a few moments of poking around, I found that the MAX232's were really hot. This happened on both boards. I popped them out and the boards appeared to work normally after that. I doubt that I actually damaged them but it was scary. A little reading online uncovered that this is a frequent complaint with these chips. I wondered if I had a bad batch from AliExpress, but it sounds like a common woe. Folks advised adding pull-ups or the like, I don't recall exactly at the moment, decided I didn't need to figure it out for now. (Although if I need to deep dive for debugging, it might come in handy. But I do have a PICKit 5, so I imagine I can just debug via that and don't really need the serial.)
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This sounds like fake or defective chips.
 
Ok ill look into what chips i have. A thought occured to me. I could try the max232 on my old frehd i bought from Ian Mavrick a buncha years back. See if that chip gets hot on my new frehd
 
That section isn't necessary for normal operation. See what is left out from a normal one (Don't look at the headers vs leds, we use them in custom cases)

Screenshot 2026-07-13 at 9.05.25 PM.png
 
Syndikated said:
Ok ill look into what chips i have. A thought occured to me. I could try the max232 on my old frehd i bought from Ian Mavrick a buncha years back. See if that chip gets hot on my new frehd
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Re overheating of the MAX232:

The "get it workiing solution" is to put a 10-20 ohm current limiting resistor between Vcc and the power supply input to the MAX232. The root cause of the problem (as mentioned above) is use of a counterfeit MAX232. Replacing it with a "real" MAX232 is the proper solution.
 
Syndikated said:
So what does that circuit actually do? Regardless of it being left in or left out I mean.
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It is an unused (optional) feature to provide Rs232 functionality normally found in Model 1 Expansion interface. Not required for FreHD hard disk functionality. Also It isn't compatible with standard RS232 and requires specific software, which doesn't exist (to know knowledge).
 
kiwisincebirth said:
It is an unused (optional) feature to provide Rs232 functionality normally found in Model 1 Expansion interface. Not required for FreHD hard disk functionality. Also It isn't compatible with standard RS232 and requires specific software, which doesn't exist (to know knowledge).
Click to expand...
Oh... I wish I would have known that. So practically noone uses that vestigial feature? Should I simply remove those components from my frehd?
 
They just refunded me with no need to send back the faulty max232 chips so that's pretty sweet! I'm glad that's behind me. Thanks again everyone for the great info and help. Im surprised I couldn't find any other threads for other people having this issue. Well lesson learned.
 
Yeah good call testing it on your old FReHD. If it runs cool there the board design is just pulling too much current through that chip, which matches what that TI thread said. If it gets hot on both boards then you definitely got a dud chip and you're out the part.
 
esnyder said:
Yeah good call testing it on your old FReHD. If it runs cool there the board design is just pulling too much current through that chip, which matches what that TI thread said. If it gets hot on both boards then you definitely got a dud chip and you're out the part.
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Thanks. Yeah I am positive they are cheap chinese knockoffs. I got my money back from the seller with no need to return the chips. Im still a little amazed that its for a serial communication that noone uses so why is it still included in the plans and BOM?
 
Syndikated said:
Im still a little amazed that its for a serial communication that noone uses so why is it still included in the plans and BOM?
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The simple answer is that it's part of the design. Effort would be required to remove it from the design and without doing so there is no good reason to remove from plans or BOM.

Whether somebody uses some feature or functionality present in the design is irrelevant.

You'd have to ask the person who designed it why they didn't release a revised version that doesn't include that.
 
Istarian said:
The simple answer is that it's part of the design. Effort would be required to remove it from the design and without doing so there is no good reason to remove from plans or BOM.

Whether somebody uses some feature or functionality present in the design is irrelevant.

You'd have to ask the person who designed it why they didn't release a revised version that doesn't include that.
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wow.. Thanks for that... :rolleyes:
 
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