• Please review our updated Terms and Rules here

Model I No Video

Don,
I've printed the three pages of components to PDF files, then OCR'd them to get a listing of all the IC's in the Model 1.
Then I imported the list to Excel and added the Pin Numbers for Vcc & GND for each IC.

With your jumpers installed from both 723C IC's Pin 7 to GND, you can now easily check the Vcc and GND Pins of all
the IC's in the Model 1. Just Highlight the ones you check and go down the list. You may want to write down any voltages
that are not +5.00VDC along with any GND Pins that are not ZERO VDC.


IC's Number Power Pin GND Pin
Z1 723C 12 7 DIP Voltage Regulator 3100001
Z2 723C 12 7 DIP Voltage Regulator 3100001
Z4 LM3900 14 7 Dual Input Norton Amp 3100002
Z5 74C00 14 7 CMOS Quad 2-Input NAND Gate 3102026
Z6 74C04 14 7 CMOS Hex inverter 3102027
Z7 74LS74 14 7 Dual D Positive-Edge-Triggered Flip-Flop with Preset and Clear 3102015
Z8 74LS153 16 8 Dual 4-Line to 1-Line Data Selector/Multiplexer 3102019
Z9 74LS04 14 7 Hex Inverter 3102008
Z10 74LS166 16 8 8-Bit Parallel In/Serial Out Shift Register 3102021
Z11 74LS166 16 8 8-Bit Parallel In/Serial Out Shift Register 3102021
Z12 74LS93 5 10 Divide by 8 Binary Counter Selector/Multiplexer 3102017
Z21 74LS156 16 8 Dual 2-Line to 4-Line Decoder/Demultiplexer 3102028
Z22 74LS367 16 8 TRI-STATE Hex Buffer 3102024
Z23 74LS32 14 7 Quad 2-Input OR Gate 3102014
Z24 74LS132 14 7 Quad 2-Input NAND Gate 3102018
Z25 74LS32 14 7 Quad 2-Input OR Gate 3102014
Z26 74LS20 14 7 Dual 4-Input NAND Gate 3102011
Z27 74LS175 16 8 Quad D Flip-Flop with Clear 3102023
Z28 74LS174 16 8 Hex D Flip-Flop with Clear 3102022
Z29 MCMB670 18 9 Character Generator 3108001
Z30 74LS02 14 7 Quad 2-Input NOR Gate 3102007
Z31 74LS157 16 8 Quad 2-Line to 1-Line Data Selector/Multiplexer 3102020
Z32 74LS93 5 10 Divide by 8 Binary Counter Selector/Multiplexer 3102017
Z33 24 12 2 K x 8 ROM A 450 ns. 2 Patterns 3108011
Z34 24 12 2 K x 8 ROM B 450 ns. 2 Patterns 3108012
Z35 74LS157 16 8 Quad 2-Line to 1-Line Data Selector/Multiplexer 3102020
Z36 74LS32 14 7 Quad 2-Input OR Gate 3102014
Z37 74LS02 14 7 Quad 2-Input NOR Gate 3102007
Z38 74LS367 16 8 TRI-STATE Hex Buffer 3102024
Z39 74LS367 16 8 TRI-STATE Hex Buffer 3102024
Z4O Z80 11 29 Microprocessor Circuit Plastic 3110001
Z41 75452 8 4 Relay Driver 3106002
Z42 74LS04 14 7 Hex Inverter 3102008
Z43 74LS157 16 8 Quad 2-Line to 1-Line Data Selector/Multiplexer 3102020
Z44 74LS367 16 8 TRI-STATE Hex Buffer 3102024
Z45 2102 10 9 AN-4L 1 K Static RAM 3108002
Z46 2102 10 9 AN-4L 1 K Static RAM 3108002
Z47 2102 10 9 AN-4L 1 K Static RAM 3108002
Z48 2102 10 9 AN-4L 1 K Static RAM 3108002
Z49 74LS157 16 8 Quad 2-Line to 1-Line Data Selector/Multiplexer 3102020
Z50 74LS93 5 10 Divide by 8 Binary Counter Selector/Multiplexer 3102017
Z51 74LS157 16 8 Quad 2-Line to 1-Line Data Selector/Multiplexer 3102020
Z52 74LS04 14 7 Hex inverter 3102008
Z53 74LS132 14 7 Quad 2-input NAND Gate 3102018
Z54 74LS30 14 7 Triple 3-Input NOR Gate 3102013
Z55 74LS367 16 8 TRI-STATE Hex Buffer 3102024
Z56 74LS92 5 10 Divide by 6 Binary Counter Selector/Multiplexer 3102016
Z57 74C04 14 7 CMOS Hex lnverter 3102027
Z58 74LS92 5 10 Divide by 6 Binary Counter Selector/Multiplexer 3102016
Z59 74LS175 16 8 Quad D Flip-Flop with Clear 3102023
Z60 74LS367 16 8 TRI-STATE Hex Buffer 3102024
Z61 2102 10 9 AN-4L 1 K Static RAM 3108002
Z62 2102 10 9 AN-4L 1 K Static RAM 3108002
Z63 2102 10 9 AN-4L 1 K Static RAM 3108002
Z84 74LS157 16 8 Quad 2-Line to 1-Line Data Selector/Multiplexer 3102020
Z65 74LS93 5 10 Divide by 8 Binary Counter Selector/Multiplexer 3102017
Z66 74LS11 14 7 Triple 3-Input AND Gate 3102010
Z67 74LS367 16 8 TRI-STATE Hex Buffer 3102024
Z68 74LS367 16 8 TRI-STATE Hex Buffer 3102024
Z69 74LS74 14 7 Dual 0 Positive-Edge-Triggered Flip-Flop with Preset and Clear 3102015
Z70 74LS74 14 7 Dual 0 Positive-Edge-Triggered Flip-Flop with Preset and Clear 3102015
Z71 Not used
Z72 74LS367 16 8 TRI-STATE Hex Buffer 3102024
Z73 74LS32 14 7 Quad 2-Input OR Gate 3102014
Z74 74LS00 14 7 Quad 2-Input NAND Gate 3102008
Z75 74LS367 16 8 TRI-STATE Hex Buffer 3102024
Z76 74LS367 16 8 TR1-STATE Hex Buffer 3102024


16K RAM LIST
A3 DIP Shunt 2100041
A71 DIP Shunt 2100041
Z13 4116 9=+5v, 8=+12v, 1=-5v 16 16384 bit Dynamic RAM 450 ns 3108009
Z14 4116 9=+5v, 8=+12v, 1=-5v 16 16384 bit Dynamic RAM 450 ns 3108009
Z15 4116 9=+5v, 8=+12v, 1=-5v 16 16384 bit Dynamic RAM 450 ns 3108009
Z16 4116 9=+5v, 8=+12v, 1=-5v 16 16384 bit Dynamic RAM 450 ns 3108009
Z17 4116 9=+5v, 8=+12v, 1=-5v 16 16384 bit Dynamic RAM 450 ns 3108009
Z18 4116 9=+5v, 8=+12v, 1=-5v 16 16384 bit Dynamic RAM 450 ns 3108009
Z19 4116 9=+5v, 8=+12v, 1=-5v 16 16384 bit Dynamic RAM 450 ns 3108009
Z20 4116 9=+5v, 8=+12v, 1=-5v 16 16384 bit Dynamic RAM 450 ns 3108009

LEVEL II ROM KIT
Z1 24 12 4K x 8 ROM. 450ns. ROM A 3108013
Z2 24 12 4K x 8 ROM. 450ns. ROM B 3108014
Z3 24 12 4K x 8 ROM. 450ns. ROM C 3108015
Z4 74LS42 16 8 BCD to Decimal Decoder 3102036


KEYBOARD INTEGRATED CIRCUITS

Z1 74LS05 14 7 Hex Buffer with open collector High Voltage outputs 3102009
Z2 74LS05 14 7 Hex Buffer with open collector High Voltage outputs 3102009
Z3 74LS368 16 8 TRI-STATE Hex Buffer 3102025
Z4 74LS368 16 8 TRI-STATE Hex Buffer 3102025



Larry


Attached is a .CSV file named as *.csv.txt



View attachment Model1IC.csv.txt
 
Last edited:
Don,
Here are a few test points for you to check also.

NO VIDEO
Check power supply voltages (note that if the 12V line is out, 5V will be to)

Shorted RAM chip can bring down voltages

Check for output at Z30 pin 1. If present, check Z41 and Q1/Q2. (Z41 could be bad if cassette relay is shorted).

Check Z9 pin 8 for SHIFT. Check output of Z26, pin 8. Check output of Z10 pin 13.

Check inputs RS1, RS2, and RS3 to Character Generator (Z29) and Address Lines from Z27 & Z28.


Larry
 
ldkraemer said:
I've printed the three pages of components to PDF files, then OCR'd them to get a listing of all the IC's in the Model 1.
Then I imported the list to Excel and added the Pin Numbers for Vcc & GND for each IC.
Click to expand...

I forgot to thank you for all the time you put into this.
 
I went down the list and verified voltage at each IC in the list. Then I verified each ground on the ICs as well. Damned if they weren't all spot on. How could this be? I removed the two jumpers and retested the voltages mysteriously showing up on Z1 pin 7 and Z2 pin 7 and they were still present. I used two different digital meters with the same result. In frustration i pulled out my trusty analog meter and... guess what, all voltage and ground pins on Z1 and Z2 were correct!

I went back to my DMMs and rechecked for voltage on the ground pins Z1, Z2 pins 7 and they again showed 13.1V and 9.5V respectively. Best as I can figure out is maybe the DMM's were picking up stray signals for the transformer on the power supply?

So I sent us down a rat hole. Well, not a complete waste of time I guess. I did get the voltage up from 10V to 12V by replacing Z2.

I guess I'm moving on to Larry's next suggestion on troubleshooting video. Is there a way to do this without a logic probe?

ldkraemer said:
...
Check for output at Z30 pin 1. If present, check Z41 and Q1/Q2. (Z41 could be bad if cassette relay is shorted).
Check Z9 pin 8 for SHIFT. Check output of Z26, pin 8. Check output of Z10 pin 13.
Check inputs RS1, RS2, and RS3 to Character Generator (Z29) and Address Lines from Z27 & Z28.Larry
Click to expand...
 
Don,
YEP, that's why old timers used a Simpson or Triplett, as they don't lie.

You are going to need a O'scope, logic probe, or a clone 8 bit logic analyzer from ebay. (I'm not a big fan of Logic Probes)

Anyway, you made good progress.

Larry
 
I have a usb logic analyzer from Saleae still new in the box. I'm weary of using usb devices to test circuits using my computer though. It would be fun to play with however... has a great display.

I also have a logic probe that would be easier to use. Hummm....
 
ldkraemer said:
... Check for output at Z30 pin 1. If present, check Z41 and Q1/Q2 ...
Click to expand...

TRS-Ian said:
On page 75 of the tech ref manual is a list of voltages to be checked on the Z1 and Z2 regulators. That is where I would start.
One you have your voltages in spec, check Z41, an 8-pin device which can contribute to a dim display. Ian.
Click to expand...

Sams ComputerFacts said:
No video on the Monitor screen. Check the waveform at the emitter ofthe Video Output Transistor (Q1), If the waveformis normal, check theVideo Connector (J2) for good connection and check the video cable.

If the waveform is missing at the emitter of Transistor Q1, check for a video signal at pin 5 of Driver IC (Z41). it the signal is present at pin 5 of IC Z41, check the voltages and components associated with Transistor O1. If signal is missing at pin 5 of IC Z41, check for a video signal at pin 6 of IC Z41. If the signal is present, check ICZ41 by substitution. lf the signal is missing from pin 6 of IC Z41, check the waveform at pin 3 of IC Z30.

If the waveform is present at pin 3 of IO Z30 and the logic reading at pin 2 of IC Z30 is Low, check IC Z30 by substitution. If the logicreading at pin 2 of iC Z30 is High, check the Shift Reg (Register) IC(Z11) by substitution. if the waveform is missing at pin 3 of IC Z30,check the waveform at pin 15 of Shift Reg (Register) IC (Z10) and check for pulses at pins 4, 5, 10, 11 and 12 of IC Z10. If the waveform and pulses are present, check IC Z10 by substitution.
Click to expand...

The signal on the emitter of Q1 is low. The signal on Z41 pin 5 is low. The signal on pin 6 of Z41 is high. So I guess I better replace Z41.
 
Don,
Do you have +5 VDC at the Collector of Q1 (same as C2 Plus side). Maybe you have lost power to that section somehow.

You can also check Pin 5 of Z41 to see if voltage is present there.

Larry
 
Don,
Check both sides of resistor R23 (one side connects to Pin 5 of Z41, and the other side goes to Base of Q1, which should have a voltage
on it from Q2 thru R28 from Q2 Collector. Also check across R23, because if the Pin 5 is shorted internally there should be voltage dropped across
R32.

It could be problems upstream of this. The SYNC signal or logic controlling it, or Q2 not supplying voltage to Q1 base.

NOTE:
My version of the PDF book has an error and has Q1 & Q2 labeled as MPS-3904. But, Q1 is a 2N3904 (NPN) and Q2 is a MPS-3096 (PNP).



Larry
 
Last edited:
Both sides of resister R23 have 0V. The base of Q1 has 0V. The Q2 collector has 0V. All 0V readings showed low on the logic probe except the Q2 collector added a blinking pulse lamp. Not sure if that is relevant. Note that on my analog multimeter I don't see very small voltages.

I checked both sides of R32 and one side had 5V, the other 4.86V.

Sams Computerfacts show Q1 as MPS3904 and Q2 as MPS3906 which is different yet.

Mod I Video.jpg
 
Don,
OK, Lets back up to the Q2 Transistor. The Emitter should have 5.0 VDC on it and the Collector should have 4.5 VDC and goes to R28,
then thru R28 to the Base of Q1, and be 4.2 VDC. The base of Q1 should have 1.1 VDC on it.

The transistors are correct. Q1 = MPS3904 NPN & Q2 = MPS3906 PNP.

Maybe you don't have +5VDC to Q2, or maybe Q2 is defective, or it's further upstream.


Larry
 
Larry, I think has the right idea--back up all the way to the 75452. What's on pins 5 and 6? If you see a pulse train on both of those pins, troubleshooting is made quite a bit simpler.
 
Q2 is getting 5V on it's emitter. The base has 4.2V (or thereabouts, analog meter). The collector, however, has nothing.

I'll look for a source of the MPS3906.
 
Don,
Hopefully this will fix it. If it does I'd put it through the paces to see if everything functions.

Larry
 
I found a source for the MPS3906 and will get it within two weeks. I'll most certainly post an update hopefully with good news. Thanks!
 
You don't need to look specifically for a Motorola part (considering that they're not made any more), any commodity 2N3906 will do--they're as common as cockroaches.
 
Chuck(G) said:
You don't need to look specifically for a Motorola part (considering that they're not made any more), any commodity 2N3906 will do--they're as common as cockroaches.
Click to expand...

i just ordered 50 cockroaches from ebay for $2.59 shipping included. <grin> Thanks for that.
 
Then you'll be delighted to know that the NPN relative, the 2N3904, is even more ubiquitous--say, as common as lice? :) To further complicate matters, a 2n2222 is often used as a substitute for the 3904--their characteristics are close enough not to matter in many cases.

If you're going to populate your hellbox with transistors these are probably the best candidates.

I'd still like to know what's going into and what's coming out of 75452 IC...
 
Last edited:
You must log in or register to reply here.
Back
Top