5v troubles while testing Core Module V2

Testing/Troubleshooting
1

Hello to all. I’ve started a Midibox SID for a friend of mine, he gave me the Core and SID modules signed on the PCB as V2 version (2002 date).

I follow the steps on the old pages for the old version and after soldering and wiring i started to test the Core module.

I checked the voltage levels as written here http://www.ucapps.de/mbhp_core_old.html and I have:

IC1:MCLR(1) - IC1:Vss(12) = 4.53V <–I’m worried about this

IC1:Vdd(11) - IC1:Vss(12) = 4.93V

IC1:Vdd(32) - IC1:Vss(31) = 4.94V

IC2(8 ) - IC2:(5) = 4.98V

Could be a problem the first line check?

Also, I noticed that when I connect the LCD cable to the display (no ICs on Core) this one it powers up (green backlight goes on) but on the Core module the bridge rectifier and the 7805 become very very very hot and i need to disconnect the LCD cause I fear to burn some components.

I’m using a PSU with an output of 16.34V and 500mA.

I’m not so sure about the mA, how could i make a measure of it?

Thanks in advance, best regards to all of you guys!

Gord The Rogue

2

MCLR @ 4.53V is okay, the 4.93V is okay as well.

Measuring current is easy, just use your multimeter parallel to the input (disconnect one of the supply wires  that go into the core and bridge it with you multimeter in current mode).

500mA is okay as well, your problem is the 16.34V you feed the 7805. The vreg needs ~7.5-10V, all the “extra volts” are turned into heat. 16V - 5V = 11V that the vreg needs to dissipate. Get a new PSU with 7.5V - 10V and the heat problem will be solved.

3

Thanks for the quick reply. I’m using that voltage because i’ve read on the old version pages that for the CORE+SID module combination 15v is needed.

The fact is that when LCD is disconnected the 7805 and the bridge rectifier don’t get hot.

Again thanks, i will re-re-recheck the LCD wiring but i’m sure is all ok.

Gord

4

While the voltages that’s dissipated is constant no matter what you hook up to the core, the current isn’t. And the heat is voltage * current. More current (LCD, …) more heat. 16V is too much for the core input. It’s okay for the SID (6581 version) module, which has a 7812 needing 15-17V input.

5

??? Uhm ok but the SID Module takes the power from the Core Module as you can see from this page http://www.ucapps.de/index.html?page=mbhp_core_old.html…

What should i do?

6

As far as i know, the power coming from the core to SID-module is 5V to drive the two 74HC595 ICs

The SID chip itself needs 9V (for 8085/6582) or 12V (for 6581)

So in fact the SID-module needs power from both the core and from a separate source

7

Thanks, now is more clear.

I was wondering if i can power directly the SID module with my supply (16v) and then chain the 12v, output of the 7812 on the SID, to the power input of the Core module.

Would it work?

Again thanks,

Gord

8

I wish i could help you on this one, but i’m really not sure…

My guess is that if the 7812 should power both SID, core + display AND go back to the SID-module to power the two 74HC595 also, then the 7812 would get very hot!

The most common solution often used inhere is to use the PSU from a C64, because it gives both 5VDC and 9VAC - i used such a solution, where the 5VDC is running the Core (connecting the 5VDC directly to where the output of the 7805 would be), and the 9VAC+5VDC is used to power the SID with 12VDC … to put 9VAC and 5VDC (giving 14VDC) together we use a small circuit called OPSU (optimized PSU) which you can see here http://www.ucapps.de/mbhp/mbhp_8xsid_c64_psu_optimized.pdf

Here is a photo of my opsu solution - as you can see it’s not that complicated, and it saves a lot of headache :slight_smile:

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5608fe8189e0ba3ffbb8051cdf48b82551c1c564e995720×480 29.3 KB

5608fe8189e0ba3ffbb8051cdf48b82551c1c564e995
5608fe8189e0ba3ffbb8051cdf48b82551c1c564e995720×480 29.3 KB

9

Update. Yes that’s the best solution, i went on with that and now i’m happy to have a working circuit. Thanks

PS Commodore’s PSU are going to be expensive and i’ve read around too much post about “old PSU failure” so i’m thinking about building a new one, just in case…