That would indicate both power switches are bad.
AGGGHHH! Stupid me. No wonder I can't remember working on one of these radios. What I was looking at as the power switch is not a switch. It's that relay I mentioned a while back. Those commonly develop bad solder connections. Of the over 200 radios I have here I don't have one like yours to look at so I have to do this from memory. There were three things I ran into very often. I think where I messed up is by having you jump the switched ignition wire to the power antenna wire. That would indeed bypass the relay and turn on the amp or power antenna, but there's additional circuitry that turns on electronically, not through that relay. Everything might have worked if you jumped those wires AND turned on the power switch. Can't say for sure though because the timing of those two things might be critical, and I never tried it.
You'll need to remove both covers, then remove four screws to allow you to lift the cassette mechanism out. Two screws on each side of the radio must be removed, then you can pry out the metal plate that sits right above the cassette mechanism. Once that plate is removed, you'll see the solder side of the circuit board. My sad drawing shows approximately where the relay sits. If there's numbers on the board, it's "K701". Look at the two left terminals to see if either one has a black ring around it like I tried to show with the red arrow. If either one looks bad, resolder both of them. If the cassette player became unplugged, you can leave it out and just plug the rest of the radio into the vehicle to try it.
That problem will cause no sound, even in vehicles that don't use a remote amp, and no switched power to the antenna or amp, but the rest of the radio may still tune stations, and the display will light up and the cassette player may still run. I can't remember for sure.
Next, look in the area of the blue arrow. There are about two dozen connections that become overheated and have to be resoldered but this is easier said than done. The new solder with its flux will not flow smoothly to make a nice shiny connection. I used to use solder wick, a special braided wire with flux in it, to remove the old solder, then the new solder flowed better. You have to be careful to not overheat those connections because most of them are for transistors. Transistors hate heat. If your soldering iron is adjustable, turn the temperature up high so you can get in and get it over with quickly. People think a lower temperature is safer but in fact, you have to sit on the connections longer to get the solder to flow smoothly, and that gives the heat time to migrate into the transistor.
Those intermittent connections cause the third problem. Some of them are in the memory circuit. They turn on two transistors in the "reset" circuit. Integrated circuits and their larger microprocessors have thousands of transistors built in that start out in random, disorganized states. They must be "reset" to their starting point as soon as power is applied. That means that reset circuit only operates when the radio is plugged in or when the battery is reconnected. It will not operate again for many years when the battery is disconnected and reconnected for some other service. The two transistors involved are only capable of passing a tiny fraction of an amp or they will overheat, but in this function they have to pass about 100 times what they're capable of, but only for a fraction of a second. It's like passing your hand through a torch flame. You can do that without injury if you're fast enough.
When the bad connections develop around that blue arrow, that circuitry can turn on and off intermittently multiple times per second as you're driving on rough roads. That mimics disconnecting and reconnecting the car's battery repeatedly, and each time it's reconnected, there's that surge of current through those transistors. Each time they heat up a little more with no time to cool down, and eventually they explode. Look on the other side of the board for "Q821" and "Q822". Hope you like green. That's what I used to show their locations. Each transistor is a small black cylinder with a flat spot and three leads. If all you see are the three wires sticking up, they've exploded. Generic replacements are not expensive. If these had failed, the radio would not turn on at all. You'd have no display, but it seems to me the cassette player would still run. It's hard not to get replacement transistors that are a lot beefier and hold up to those repeated surges better, and if someone replaced them already, they could look different. There's a lot of different shapes and sizes but they'll all have three leads.
As a side note not related to your radio, there is a newer model that had a 100 percent failure rate of that reset circuit. Since it's not needed once the microprocessor is running, it can fail and no one will ever know it until the battery is disconnected for some other service or it runs dead. Mechanics often have to disconnect the battery, then they get blamed unfairly for causing the radio to be dead. The problem actually occurred months or years earlier but only shows up when the battery is reconnected. I compare that to a starter motor falling off the engine while you're driving. You'll never know it until after you stop and try to restart the engine.
Anyhow, start with those tests. The fact that you have continuity from pin 5 to the power antenna wire proves the fusible resistors are okay and nothing is shorted in the amp or the wire going to it. I was thinking about relay connections but I failed to see all of that relay on the schematic diagram. I think I'll blame that on my aging eyes.
Thursday, December 13th, 2012 AT 4:21 AM