ATARI 65XE - No image or maybe dead?

[Jangle]

21 minutes ago, Nezgar said:

BASIC is a 2364 mask ROM, so Vcc should be pin 24.

OS ROM (23128) Vcc should be pin 28.

MMU Vcc should be pin 20.

Thanks!

Results:

BASIC => 4.82

OS ROM => 4.82

MMU => 4.88

 

Now I connected to the TV in channel 2 and 3 and it seems that wants to get signal (before I was only testing on Monitor plug).

At least the signal changes when is powered on.

That means something to you ? Never tried RF because Monitor has more definition and was more simple to make the cable (and I wasn't have an antenna cable adapter too)

[xrbrevin]

i heard that the MMU is just a re-badged GAL chip

[shoestring]

The ones I've seen all look like re-branded PALs.  The ones I have in-front of me are MMI re-branded with c061618 instead of PAL16XXX with date codes around 83.  GALs weren't introduced until 1985 but you might be able to find one in an XE?

 

And here is one manufactured by National Semiconductor.

 

 

[Jangle]

I tried again and now I get a perfect BLACK SCREEN on channel 3 at 61.35MHz with RF

But at 60.5MHz (using Tune Fine) gives me this:

 

Monitor plug sends no signal.

That's no good news right?

 

Measuring with Multimeter the monitor output gives me:

PIN 1 => 1.29

PIN 4 => 0.31

PIN 3 => 0.36

PIN 5 => 0

 

[Jangle]

I check the service manual of 130XE and in the section of Troubleshooting says:

BLACK SCREEN could be +5VDC, L4-L8, ANTIC, CR8, Power Plug, SW1, Y1

 

I don't have CR8 but I have CR5 (Zener diode ? I don't know if they are the same) near of Y1 and gives me polarity on both sides.. 

Could that be the only problem ?

The other three (CR2,CR3,CR4) are measuring normal..

 

 

 

 

 

 

And now I found this :

 

 

What would cause that Diode to short circuit?

Edited March 24, 2020 by Jangle

[_The Doctor__]

cr5-lift one leg and test out of circuit

c202-make sure that's a print smear on that and not a heat discoloration

Edited March 24, 2020 by _The Doctor__

[Jangle]

8 hours ago, _The Doctor__ said:

cr5-lift one leg and test out of circuit

c202-make sure that's a print smear on that and not a heat discoloration

Yes! I saw that too but unfortunately I don't have an Inductance Meter so I'll have to wait after the quarantine to get one

The cr5 is behaving strangely.. When the machine is plugged but not powered gives me polarity on both sides.

But when the machine is on , is behaving "normally" (I don't test it with one leg lift but I will)

An another thing is that I don't get any voltage around him..so maybe is the POKEY? Between leg 16 and cr5 don't get any voltage neither..No amps too , only continuity.

 

So I think that is all for now

Thank you all for the support!

 

 

 

Edited March 24, 2020 by Jangle

[xrbrevin]

some diodes have an operating range that makes them only block current up to a certain point

look up the datasheet for the diode component number in question to see if is intended/designed to have this function

[Jangle]

7 hours ago, xrbrevin said:

some diodes have an operating range that makes them only block current up to a certain point

look up the datasheet for the diode component number in question to see if is intended/designed to have this function

Yes that's what I thought but there is too much manufacturers for this diode (1N4148)

I don't know if they are different on specs
https://www.alldatasheet.com/view.jsp?Searchword=1n4148 datasheet&gclid=CjwKCAjw3-bzBRBhEiwAgnnLCt96WVJkp1XXia0XNh6fsFqITvXWKc02JdxbmmihfKIPsKOX1MCXXRoCXysQAvD_BwE

 

But just peeking one :

https://www.alldatasheet.com/datasheet-pdf/pdf/733245/SURGE/1N4148.html

 

I don't understand too much but I think the Foward Current (normal diode behave) is MAX 1v and beyond that (when works in reverse orientation) the Reverse Breakdown Voltage could be 5/25/50v?

 

Edited March 24, 2020 by Jangle

[_The Doctor__]

to stabilized reference voltage as well as protecting against over-voltage from electrostatic discharge perhaps... in which our nearby buddy needs both of those characteristics.

[Atari_65XE]

https://www.youtube.com/watch?v=rUl8qhO2Nec&t=1909s

 

This guy had a video screen red and nothing else happening. He replaced all the chips only to find the last chip to be the culprit. He told me it was the most common chip of all, NE555 timing.
I have the same black screen issue as you. I replaced my 555 but it didn't fix. I'm on the same adventure you are on. Good luck and I'll post if I find anything to help.

[shoestring]

The 555 timer is part of the reset circuit, so if it's broke the CPU will just sit there waiting for a RST pulse with its outputs stuck. But I don't think that's OP's problem.