I've had a battery leak in my FM4. The green LED failed. R12 2k2 was open circuit.
I have replaced these and cleaned up the mess. The unit works happily, but if not used for a week or so, the preset stations are lost. A few seconds of operation after turn on allow them to be re-entered and stored and everything is back up to normal.
The obvious conclusion is that the battery is drained if left to its own devices for too long after the unit is turned off. A quick look at the circuit diagram suggests c12 now presents too low a resistance path to earth. Barring the replacement battery being bad, would that be the obvious conclusion or is there another more obvious discharge path I have missed?
Many thanks for your thoughts.
kind regards
Marek
I have replaced these and cleaned up the mess. The unit works happily, but if not used for a week or so, the preset stations are lost. A few seconds of operation after turn on allow them to be re-entered and stored and everything is back up to normal.
The obvious conclusion is that the battery is drained if left to its own devices for too long after the unit is turned off. A quick look at the circuit diagram suggests c12 now presents too low a resistance path to earth. Barring the replacement battery being bad, would that be the obvious conclusion or is there another more obvious discharge path I have missed?
Many thanks for your thoughts.
kind regards
Marek
How is the condition of the battery holder and circuit board area nearby? One possibility is that a leaking battery might damage some of the "insulators" and make (poor, but significant) conductive tracks. If C12 is an electrolytic it should of course be replaced prophylactically.
All good fortune,
Chris
All good fortune,
Chris
C12 being leaky wouldn’t have that effect. It would shift all your tuning down the dial.
The battery has leaked and now isn’t holding a charge, so it has had it, but rather than just replacing it you should consider Quad’s new IC1 that doesn’t need a battery at all. Contact me off list for details.
EJP
The battery has leaked and now isn’t holding a charge, so it has had it, but rather than just replacing it you should consider Quad’s new IC1 that doesn’t need a battery at all. Contact me off list for details.
EJP
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Thank you Chris. The unit had no battery holder. I guess I'll pull the circuit board out and clean it down at some point when I have time. The new battery appears to be fine.
Except that it isn't holding a charge. It would be useful to measure its voltage before next time you turn it on, and immediately after you turn it off. Nominally 4.8V.
Pulled it apart after several days' inactivity. Battery reads 5.08V after several days unpowered. Holds charge. Station presets retained. Rechecked after having it turned on for a minute - still 5.08V.
kind regards
Marek
kind regards
Marek
Postscript:-
After a long interval of inactivity, the battery drained and the tuner display sat at minimum 87.3 and wouldn't tune manually. Diagnosis X gives four reasons why this might happen. New capacitors for c10-c12 went in. c10 looked to have one leg barely attached. I peeled back the plastic shroud on the new battery and observed that two of the cells were clearly good and two were partially discharged. The (new) battery clearly wasn't in marvelous shape then. I observed that when IC1 wasn't in its socket, the battery didn't drain, so I concluded that either IC1 didn't shut down at switch off or there was excessive conductivity between IC1 socket pins. Careful examination showed not all of the socket pins looked to be conducting properly, so I replaced the socket. This restored the tuner. Excessive battery drain dropped.
Reading all of the threads on DIYaudio regarding the FM4, it's clear that the 7812 runs hotter than is sensible, since the board was blackened around it. I replaced the 7812 since I have tons of those to hand. This was a mistake, as not all 7812s are created equal. Prior to replacing the socket, the new 7812 would drop out after a few minutes and the voltage collapse. Replacing it with the old 7812, this didn't happen, so I'd conclude that the safe operating area of ebay bulk purchased 7812s is nowhere near as good as the National Semiconductor 7812 Quad fitted when it comes to temperature. It also prompted me to investigate why the current draw was higher than I'd like. Quad missed a trick when they introduced the little heatsink on Tr9. They could have mounted it on the metal screening shroud instead of adding a paltry little Z shaped heatsink. Also, the screen happens to be the same height as the smaller computer fans, so I punched a hole in it and mounted a tiny 12v fan to pump air onto electrolytic caps and 7812. This makes the power supply run cool, even when left on over 24 hours. The outer casing has enough tiny 1mm gaps for air to be drawn in and pushed out at the four pcb corner mounting bolts. I left it running to check stability and to see whether the battery charged fully. The tuning remained rock solid. The three of the four 1.2v cells charged up to 1.3-1.32v and the fourth got to 1.26v. The unit runs cool now. The metal shrouding box isn't even vaguely warm to the touch.
I'd like to thank ejp for posting so much useful information here - combine it with the service manual and there is enough diagnostic information to get a non-working FM4 back up. IC1 is more robust than it first seems, but the soldering and socket integrity are a hidden (but known) problem as confirmed by the service manual instructions. When in doubt, read the manual.
kind regards
Marek
After a long interval of inactivity, the battery drained and the tuner display sat at minimum 87.3 and wouldn't tune manually. Diagnosis X gives four reasons why this might happen. New capacitors for c10-c12 went in. c10 looked to have one leg barely attached. I peeled back the plastic shroud on the new battery and observed that two of the cells were clearly good and two were partially discharged. The (new) battery clearly wasn't in marvelous shape then. I observed that when IC1 wasn't in its socket, the battery didn't drain, so I concluded that either IC1 didn't shut down at switch off or there was excessive conductivity between IC1 socket pins. Careful examination showed not all of the socket pins looked to be conducting properly, so I replaced the socket. This restored the tuner. Excessive battery drain dropped.
Reading all of the threads on DIYaudio regarding the FM4, it's clear that the 7812 runs hotter than is sensible, since the board was blackened around it. I replaced the 7812 since I have tons of those to hand. This was a mistake, as not all 7812s are created equal. Prior to replacing the socket, the new 7812 would drop out after a few minutes and the voltage collapse. Replacing it with the old 7812, this didn't happen, so I'd conclude that the safe operating area of ebay bulk purchased 7812s is nowhere near as good as the National Semiconductor 7812 Quad fitted when it comes to temperature. It also prompted me to investigate why the current draw was higher than I'd like. Quad missed a trick when they introduced the little heatsink on Tr9. They could have mounted it on the metal screening shroud instead of adding a paltry little Z shaped heatsink. Also, the screen happens to be the same height as the smaller computer fans, so I punched a hole in it and mounted a tiny 12v fan to pump air onto electrolytic caps and 7812. This makes the power supply run cool, even when left on over 24 hours. The outer casing has enough tiny 1mm gaps for air to be drawn in and pushed out at the four pcb corner mounting bolts. I left it running to check stability and to see whether the battery charged fully. The tuning remained rock solid. The three of the four 1.2v cells charged up to 1.3-1.32v and the fourth got to 1.26v. The unit runs cool now. The metal shrouding box isn't even vaguely warm to the touch.
I'd like to thank ejp for posting so much useful information here - combine it with the service manual and there is enough diagnostic information to get a non-working FM4 back up. IC1 is more robust than it first seems, but the soldering and socket integrity are a hidden (but known) problem as confirmed by the service manual instructions. When in doubt, read the manual.
kind regards
Marek
