Hello--
Got another interesting amp I would like to repair. This time its a 4ch(?) ford JBL amp from a 1986 Lincoln Continental (E65F-18B849-AA). What's intriguing about this system is the head unit was designed to work strictly with this amp, and neither are designed to work as a standalone. The case of the amp also holds some sort of transformer / power supply that cannot be inspected. Also from what I have learned, this particular amp was a 1-2 year only design before it got changed, making it very difficult to find another drop in replacement.
Symptoms are, when the radio is turned on, I get a loud pop at all the speakers, then silence with the slightest sound of scratching in the speakers. None of the radio controls affect the output at the speakers. The radio has been confirmed to work, and I am getting audio at the input of the amp.
I reached out to "the guy" who works on these old ford electronics, and he said not only is it older than what he works on (1988-1994 amps) but it is completely different internally than the later ones. He also does not have any of the schematics for it. While talking with him, he said usually the Sanyo STK2240 amp packs (qty 2) usually fail, and can sometimes take other parts out down the line. Just out of a whim, I replaced the amp packs with no change.
I am unsure of what to start checking. Without knowing the pinout of the main power plug, I cannot bench test the amp. I am going to just assume its +12v through the fuse, then GND at the case, but I dont know if one of the wires is an enable, or if the head unit controls power with a relay. I would assume I need to solve the power input before testing can proceed.
In the pic, the bottom row of wires are the input, and the plug on the left of the board is the power input, and speaker outputs.
Once that is solved, what should I check first? My pictures are lacking, but that can be corrected later if need be.
Got another interesting amp I would like to repair. This time its a 4ch(?) ford JBL amp from a 1986 Lincoln Continental (E65F-18B849-AA). What's intriguing about this system is the head unit was designed to work strictly with this amp, and neither are designed to work as a standalone. The case of the amp also holds some sort of transformer / power supply that cannot be inspected. Also from what I have learned, this particular amp was a 1-2 year only design before it got changed, making it very difficult to find another drop in replacement.
Symptoms are, when the radio is turned on, I get a loud pop at all the speakers, then silence with the slightest sound of scratching in the speakers. None of the radio controls affect the output at the speakers. The radio has been confirmed to work, and I am getting audio at the input of the amp.
I reached out to "the guy" who works on these old ford electronics, and he said not only is it older than what he works on (1988-1994 amps) but it is completely different internally than the later ones. He also does not have any of the schematics for it. While talking with him, he said usually the Sanyo STK2240 amp packs (qty 2) usually fail, and can sometimes take other parts out down the line. Just out of a whim, I replaced the amp packs with no change.
I am unsure of what to start checking. Without knowing the pinout of the main power plug, I cannot bench test the amp. I am going to just assume its +12v through the fuse, then GND at the case, but I dont know if one of the wires is an enable, or if the head unit controls power with a relay. I would assume I need to solve the power input before testing can proceed.
In the pic, the bottom row of wires are the input, and the plug on the left of the board is the power input, and speaker outputs.
Once that is solved, what should I check first? My pictures are lacking, but that can be corrected later if need be.
Attachments
i made an account last night but never received the account confirmation. yes, also checked spam.
the only thing i could find on there was a post called 1986 and up ford radio plugs. doubtful it would have the amp wiring. guess ill let you know when i find something out.
Can you eliminate all of the wires that cannot be used to control the amp like speaker wires? What's left?
What IC does the amp use to drive the FETs?
What IC does the amp use to drive the FETs?
Loosely. It only uses 6 pins at the radio due to a shared ground, but at the amp they break the ground out so each channel has their own.
Yes. The wires at the bottom are all input, the wires in the middle are output. Only ones I don't know are:
Yellow / black tracer
Small orange
Large Red
The radio doesn't directly feed power to the amp. My guess is the large Red and yellow / black tracer are power wires and the small orange is enable. Yellow / black feeds into the transformer on the case, red lands under the PCB next to the solid yellow case transformer output, and small orange is near the switching (?) transformer.
Not sure which ic you are wanting specifically. I made a key of all the ics and fets. Let me know if it doesn't make sense
A large wire that reads 0 ohms to leg 3 of the BUZ71s is likely the ground.
A large wire that reads 0 ohms to the center leg of the BUZ71s is likely the B+ (battery) wire.
The TL594 is the PS driver IC. I'm not sure how power gets to it (through some remote turn-on wire) but it will feed pin 12 and likely pins 8 and 11.
What are you going to use to power this for testing?
Don't throw the old STK modules away. New ones are VERY commonly counterfeit and second-rate if the originals are discontinued.
A large wire that reads 0 ohms to the center leg of the BUZ71s is likely the B+ (battery) wire.
The TL594 is the PS driver IC. I'm not sure how power gets to it (through some remote turn-on wire) but it will feed pin 12 and likely pins 8 and 11.
What are you going to use to power this for testing?
Don't throw the old STK modules away. New ones are VERY commonly counterfeit and second-rate if the originals are discontinued.
Large orange is ground, large yellow is B+
Unsure on the small orange.
On the TL594 all three pins are connected but I cannot determine where they go. The traces are on the underside of the board. Want me to remove the board and get a picture?
I still have them but I cut the legs to remove them. Salvageable but it'd be a pain.
How many wires are unknown other than the small orange?
What are you going to use to power this for testing?
What are you going to use to power this for testing?
Just that one I think. I don't know the specific channels for the input/output wires, but I do know which set of wires are for the input and output.
Sorry. I have a 10a 13.8v pyramid bench supply, unless the amp pulls more than that at idle. I don't have any supplies that are adjustable.
If the orange wire doesn't have 12v on it, it's likely the turn-on wire. You can ask the guy who works on Ford equipment for his opinion.
Have all heatsink-mounted components tightly clamped to the heatsink before you try to power the amp up.
Have all heatsink-mounted components tightly clamped to the heatsink before you try to power the amp up.
I'll ask but he isn't much of any help as I've asked for the later amp connector pinouts to compare to mine with no response.
Once power is applied, what should I be looking for? Hot fets on the heat sink?
High current draw is the first thing to look for. It may be difficult to notice if your supply has no amp meter. The FETs may heat up but that may take longer than it takes to damage them.
Do you have an old incandescent headlamp or maybe a 300w 120v halogen worklight that you could use as an inline limiter on the 12v line?
Did any fail, originally?
Can you measure the voltage on the head unit's wire that goes to the orange wire to see if it goes from 0v to 12v when the head unit is switched on?
Do you have an old incandescent headlamp or maybe a 300w 120v halogen worklight that you could use as an inline limiter on the 12v line?
Did any fail, originally?
Can you measure the voltage on the head unit's wire that goes to the orange wire to see if it goes from 0v to 12v when the head unit is switched on?
I can hook my meter in line as it's good up to 10amp.
I've got old sealed beam bulbs. Gonna suck having that on my bench while testing but I'll do it. I assume dim is okay, bright means high amp draw?
I can't say. It's common for these amps to fail, but usually it's just the Sanyo packs. There's nothing blown up or damaged that I can see. Only thing I changed were the Sanyo packs.
I'll check the orange wire tomorrow. Got tied up helping with a buddy resembling his engine today.
the small orange is enable. radio off, 0v. radio on, 12v
put my meter in line with the power supply and it read 884mA with the amp enabled. i checked pins 8 11 12 on the tl594 and they showed 10.3v. not sure if that matters a whole lot. seems kinda odd theres a voltage drop on those pins.
i take it maybe the next step is to either check power at other points in the amp, or maybe feed a signal into it and see where it gets dropped?
pardon my ignorance, whats the purpose of the buz71 fets if the stk2240 handle most of the amplification?
Factory wiring diagrams should give you the full pinouts. They may not be explicit - you might have to follow the colors back to other diagram sections.
The BUZ71s are typically for the switching power supply top boost the available voltage for audio.
What's easier, applying signal and checking for audio or posting the voltage on the components clamped to the end of the amp (BUZ71s and other components)?
What's easier, applying signal and checking for audio or posting the voltage on the components clamped to the end of the amp (BUZ71s and other components)?
thats kinda what i thought with the buz71's.
objectively, applying a signal would be easier. about half of the buz71's are jammed behind the transformer and are nearly inaccessible. if needed, i can make something work though. up to you, really. tell me what to check / apply and i will make it happen.