fix retro game 1978 Electronic Quarterback

[jurgyman]

It will be an easy fix... the red wire to piezo speaker has become unattached.
but not sure where to solder it!  Whom can assist!  missing out on some beep, beep, beeps!

[mbless]

Give a better close up of the PCB around the middle left

[Twoflower]

If you do a right click on the image and there 'Show image' you get a full resolution picture of the board. Still it is hard to say.

Maybe do a picture from the other side of the PCB as well. As this might help to identify a kind of amplifier. For example often there is a coil used to reach a higher voltage to drive the piezo-speaker.

[mbless]

If you do a right click on the image and there 'Show image' you get a full resolution picture of the board. Still it is hard to say.

Maybe do a picture from the other side of the PCB as well. As this might help to identify a kind of amplifier. For example often there is a coil used to reach a higher voltage to drive the piezo-speaker.

Already did that, couldn't see anything.

OP, most solder joints will be smooth. You want to look for one that has a divot where the wire would fit.

[Twoflower]

Ok, many folks just miss that sometimes that this is a way to get a higher res picture. 

I have two potential spots identified (see below). But I can't say for sure that one of them is the real one. The upper one as it has a solder blob with a similar size to the GND (the other) connection. But as the trace is wide it could be a GND of supply trace. The lower one as it looks somehow different. Can you check if these looking like a wire was attached?

[ebastler]

Looks like somebody has messed with that board already, during an earlier repair (attempt?). Lots of manually resoldered joints with resin residue, and it looks like one of the pads has gone missing for the large IC. So maybe they have also resoldered the joint which had the speaker connected, and have tampered with the evidence?

[jurgyman]

even with magnifying glass I cant tell from looking at solder points where the red wire went...
I am the original owner of this 40 year old device. No fixing/mods have occurred AFAIK.

as requested, full board front and back shots:

[Cyberdragon]

Neither of the two suggested locations makes any sense electrically. One of those is a power rail for the logic chips, the other is a data line for the display.

The chip datasheets are available and may help.

[james_s]

The lead that is connected goes to what looks like a ground or power rail. I would look closely at the circuit and first see if any of those transistors has a pin that's flapping in the breeze. If they all appear to be connected to something already then follow each pin out of the CPU looking for one that doesn't lead anywhere.

Since it's just a piezo disc it will present minimal load to the circuit so there is virtually no risk in connecting it somewhere you suspect may be right to see if it works.

[Cyberdragon]

No, all those transistors are for LED muxing.

EDIT: All the CPU leads appear to be used. It's probably on one of those MUXing buffer chips above. Which are being PHANTOM POWERED! Their VCC pins are disconnected! Absolutely terrible design!

That pin first mentioned is probably the speaker connect and where they are shoving power up it's arse through one of it's outputs!

[alank2]

Double row bubble LED display?  Interesting!

[Twoflower]

Very strange. But there's a vacant hole visible at the top side of the PCB, just above the 'upper' position I mentioned. In the new pictures left of the marked position. Even as it might not make any sense. But I haven't tried to understand the schematics. And there is a potential short at the display.

[floobydust]

I took my Coleco Electronic Quarterback apart, circa 1978 but it's Rev. D circuit is a bit different from your Rev. B,
Yours has discrete transistors, CD4066 IC is what I have. Rev. D may use a louder piezo drive scheme.

Both use SN75492 as driver IC for the LED bubble display and piezo buzzer. I think the MCU is the same mask ROM. It is a TI TMS1100NLL, MP3415 DBS, datecode 7840.

I traced the piezo buzzer out, and the main signal comes from MCU pin 3 and then to inverter input SN75492 pin 10, with the piezo buzzer (red) connecting to pin 9 SN75492 output.
This is the same as your circuit. Piezo (white) connects to pin 10 SN75492, or could go to GND but quieter then. Nobody likes quiet touchdowns lol.

A Q-tip with isopropyl alcohol can clean up the PCB flux.

edit: I thought the bubble LED display was a two-line 7 segment type, but the bottom row just has two LEDs per bubble.

You can cheat a bit on the game, a weak 9V battery makes the opposing team move really slow (low clock speed) and switch bounce helps you move super fast.

[Cyberdragon]

I took my Coleco Electronic Quarterback apart, circa 1978 but it's Rev. D circuit is a bit different from your Rev. B,
Yours has discrete transistors, CD4066 IC is what I have. Rev. D may use a louder piezo drive scheme.

Both use SN75492 as driver IC for the LED bubble display and piezo buzzer. I think the MCU is the same mask ROM. It is a TI TMS1100NLL, MP3415 DBS, datecode 7840.

I traced the piezo buzzer out, and the main signal comes from MCU pin 3 and then to inverter input SN75492 pin 10, with the piezo buzzer (red) connecting to pin 9 SN75492 output.
This is the same as your circuit. Piezo (white) connects to pin 10 SN75492, or could go to GND but quieter then. Nobody likes quiet touchdowns lol.

It seems the Vss pin is just protection diodes, the darlingtons appear to be self biased.

In this circuit, they've shunted one of the outputs to positive and connected the piezo to ground (constant potential) so when the signal comes in it grounds both sides.

Is that a 1 , 1K , or 10K resistor? (too much glare on that band) If it's a one ohm that's chip abuse and you should get rid of it!

[floobydust]

This game led me to the first microcontroller, Texas Instruments 4-bit TMS1000 1974. Quite an adventure into the history of MCU's. US Patent 3,757,306.

The circuit is the piezo and 10k pullup to +9V, and other leg of piezo to the MCU pin 3, or OP's goes to GND instead. The SN75492 Darlington array is similar to ULN2004.

Mask ROM here is indeed "MP3415" and Sean Riddle read out the MP3460 firmware from these chips, using solvent on the IC package and probes. They are all available in MAME ROMS.

His H/W description also confirms the piezo buzzer wiring. Taken from http://seanriddle.com/h2hfb.txt

Code: [Select]

Coleco Head To Head Football

Chip labeled 
TMS1100 NLLE
MP3460
WE 8018

die labeled
MP3460

9 buttons
3 switches: Skill 1/Skill 2, Run Kick / Pass, 1 Player / 2 Players
9 7-segment LEDs (DP is under digit, digit 3 only has segments A, D, G and DP)
8 LEDs to the right of digits 2-9
Piezo buzzer


TMS1100 pinout
1  R8   - digit 1 (rightmost) and Defense Left button
2  R9   - LEDs between digits
3  R10  - Piezo
4  VDD  - 9V -
5  K1   - key matrix - 1 or 2 Players switch
6  K2   - key matrix - Pass or Run/Kick switch
7  K4   - key matrix - Skill 1 or 2 switch
8  K8   - key matrix - buttons
9  INIT - VDD
10 O7   - segment below digit
11 O6   - LED segment G
12 O5   - LED segment F
13 O4   - LED segment E
14 O3   - LED segment D
15 O2   - LED segment C
16 O1   - LED segment B
17 O0   - LED segment A
18 OSC1 - connected to OSC2 and 100pF disc cap (to VSS) and 39K resistor (to VDD)
19 OSC2 - OSC1
20 VSS  - 9V +
21 R0   - Digit 9 (leftmost) and Skill 1 Switch, Pass switch, 1 Player switch and Offense Left/Right button
22 R1   - Digit 8 and Skill 2 Switch, Run/Kick switch, 2 Players switch and Offense Down button
23 R2   - Digit 7 and Offense Up button
24 R3   - Digit 6 and Offense K/P button
25 R4   - Digit 5 and Offense D button
26 R5   - Digit 4 and Defense Down button
27 R6   - Digit 3 and Defense Up button
28 R7   - Digit 2 and Defense Right button


button matrix
        K1          K2           K4           K8
R0   1 Player      Pass       Skill 1    Offense Left/Right
R1   2 Players   Run/Kick     Skill 2    Offense Down
R2                                       Offense Up
R3                                       Offense K/P 
R4                                       Offense D
R5                                       Defense Down
R6                                       Defense Up
R7                                       Defense Right
R8                                       Defense Left

[marty]

Datasheet or manual for the TMS1000 series chips if your interested.

http://www.filedropper.com/tms10001100

[Bigkim]

These units are as cheap as chips on EBay, just buy another working unit, open it, and see where the connections go, or just keep the working one.

[jurgyman]

piezo red to MCU 3 fixed the audio.
thanks all!