Customer brought in a AKAI GX747 reel deck the other day. Citing no record. That problem was fairly simple to fix: Rly-1 had an open field coil and was muting the audio permanently on record.
Customer had this deck in an automotive repair shop for over 30 years. Found much soot in and outside of the deck. Customer also sprayed chemicals into the sliding switch for the FWD/REV modes. Bottom PCB was full of oil and dust. Cleaned this PCB when I replaced the relay.
Deck records beautifully in both directions now. Only problem is, what was recorded on Side 2 of the tape gets erased when recording on Side 1, and visa-versa--side 1 is erased when recording side 2.
The Track selector switches don't work either. Audio continues to be recorded to both channels if one or the other track selector is set to off position. More oddly, I decided to time the switching and then play back the reverse side of the tape to see if it had any effect on erasure. It sure did! Turning off one switch ceased erasure of one previously recorded track and turning off the other ceased erasure of the other previously recorded track.
My gut tells me someone may have pulled a bunch of connectors and then put them back in the wrong sockets. When in record mode, both FWD and REV erase heads have 100KHz at about 80V P-P. WTF?
I also found a solder short between the Tape Selector switch terminal and an adjacent connection to C29B. I removed that short and reflowed a bunch of questionable joints, but alas, nothing changed.
I e-mailed the customer, asking who serviced this deck before.
And yes, I made sure the slide switches (both of them) were fully engaged and checked the readings on the contacts to make sure the switch was really shorting the correct pins. Even so, deck still erases all tracks when recording either 2 tracks.
Have I missed something? Before this rolls into too many hours, I may have to tell the customer this is not fixable, short of a costly analysis of every wire and every trace and disassembly of every switch related to this function.
Customer had this deck in an automotive repair shop for over 30 years. Found much soot in and outside of the deck. Customer also sprayed chemicals into the sliding switch for the FWD/REV modes. Bottom PCB was full of oil and dust. Cleaned this PCB when I replaced the relay.
Deck records beautifully in both directions now. Only problem is, what was recorded on Side 2 of the tape gets erased when recording on Side 1, and visa-versa--side 1 is erased when recording side 2.
The Track selector switches don't work either. Audio continues to be recorded to both channels if one or the other track selector is set to off position. More oddly, I decided to time the switching and then play back the reverse side of the tape to see if it had any effect on erasure. It sure did! Turning off one switch ceased erasure of one previously recorded track and turning off the other ceased erasure of the other previously recorded track.
My gut tells me someone may have pulled a bunch of connectors and then put them back in the wrong sockets. When in record mode, both FWD and REV erase heads have 100KHz at about 80V P-P. WTF?
I also found a solder short between the Tape Selector switch terminal and an adjacent connection to C29B. I removed that short and reflowed a bunch of questionable joints, but alas, nothing changed.
I e-mailed the customer, asking who serviced this deck before.
And yes, I made sure the slide switches (both of them) were fully engaged and checked the readings on the contacts to make sure the switch was really shorting the correct pins. Even so, deck still erases all tracks when recording either 2 tracks.
Have I missed something? Before this rolls into too many hours, I may have to tell the customer this is not fixable, short of a costly analysis of every wire and every trace and disassembly of every switch related to this function.
Hi Mark if no one here can suggest a fix it may be worth asking on the Tapeheads.Net site ,the sites dedicated purely to analog recording etc and seems to have some very knowledgeable members.
There's you clue, both erase heads are operational....it sounds like switching is your problem.
The Erase frequency/voltage is correct.
The service manual is easily Googled.
Dan.
I'll have to sign up for that forum and give it a try.
I suspected the switch, so I removed and inspected and cleaned and reassembled it and tested with an ohmmeter. It tests correctly, but when in the deck, the results are inconsistent. The peculiar thing is that it only records properly when this switch is only 2/3 engaged. If I slide it all the way over (where I tested its continuity), the deck has a very high level in one channel and nothing in the other.
I also checked the playback switch to its right, but in-circuit, and it checks out with an ohmmeter. I was hoping to find a situation where both contacts were making contact, but that wasn't the case. Switches are not at fault, other than being hard to operate (sliding action is not smooth, so when the deck switches, results are inconsistent.)
The larger switch is not salvageable in terms of getting it to ever slide smoothly. Someone sprayed too many cleaning chemicals into it over the years and the nylon trolly expanded and has cracks in it. But manually operated, it works as a switch. Just the deck doesn't work properly, when this switch is fully engaged and making the connections that should be made.
The trouble with something like this is that other hands have been in the deck before mine. I don't know what else was done to it. And the amount of soot and grease I found inside and outside of it is alarming. This spent it's entire life in an auto repair shop.
I suspected the switch, so I removed and inspected and cleaned and reassembled it and tested with an ohmmeter. It tests correctly, but when in the deck, the results are inconsistent. The peculiar thing is that it only records properly when this switch is only 2/3 engaged. If I slide it all the way over (where I tested its continuity), the deck has a very high level in one channel and nothing in the other.
I also checked the playback switch to its right, but in-circuit, and it checks out with an ohmmeter. I was hoping to find a situation where both contacts were making contact, but that wasn't the case. Switches are not at fault, other than being hard to operate (sliding action is not smooth, so when the deck switches, results are inconsistent.)
The larger switch is not salvageable in terms of getting it to ever slide smoothly. Someone sprayed too many cleaning chemicals into it over the years and the nylon trolly expanded and has cracks in it. But manually operated, it works as a switch. Just the deck doesn't work properly, when this switch is fully engaged and making the connections that should be made.
The trouble with something like this is that other hands have been in the deck before mine. I don't know what else was done to it. And the amount of soot and grease I found inside and outside of it is alarming. This spent it's entire life in an auto repair shop.
Hi Mark,
I'd wash my hands of it. The erase oscillator is loaded down some as I think the voltage might be a touch low, confirmed by the fact that it erases both sides of the tape. At fist I thought it might have been the record head at the wrong level, but your later comments make me doubt that. Still, check the simple, stupid things as well. On this you can't assume anything. I suspect that you had a panicking "technician" in there. That means things may have been done that don't make any sense at all.
I recently worked on a tuner (McIntosh) that some idiot had aligned the IF frequency to around 10 MHz, not the expected 10.7 MHz (as it should have been). That didn't make any sense, and it took a long time to align it that way. So don't count anything out on this one.
Good luck on this one. Don't let your pride suck you into too much time on it!
-Chris
I'd wash my hands of it. The erase oscillator is loaded down some as I think the voltage might be a touch low, confirmed by the fact that it erases both sides of the tape. At fist I thought it might have been the record head at the wrong level, but your later comments make me doubt that. Still, check the simple, stupid things as well. On this you can't assume anything. I suspect that you had a panicking "technician" in there. That means things may have been done that don't make any sense at all.
I recently worked on a tuner (McIntosh) that some idiot had aligned the IF frequency to around 10 MHz, not the expected 10.7 MHz (as it should have been). That didn't make any sense, and it took a long time to align it that way. So don't count anything out on this one.
Good luck on this one. Don't let your pride suck you into too much time on it!
-Chris
I agree, anatech, this deck is a nightmare on the inside and who knows what the soot is doing to the electrical connections in places I can't see?
I own a 747dbx myself, which I purchased from Japan in April of '84, and I have had nothing but yeoman service from it for all these years, until recently the tension arm belts gave up, so they hunt when there's no tape loaded. Deck still records and plays and meets spec after all these years, too. So when the customer brought in his 747 model (with the LED VU meters), I kind of felt a paternal instinct toward reviving it, if you know what I mean. 🙂
But the harsh environment the 747 has had to endure, plus the all day long play (he said he used it every day since he bought it new in the 80's) wear and tear and the unknown technician repairs (that solder bridge I found was concerning), plus the fact that the customer sprayed cleaning solutions into the FWD/REV sliding switch which probably ruined the nylon/plastic trolley that carries the contacts, all makes me think that further efforts to solve this would be economically absurd.
My initial repair was to fix a 'no record' problem. Replacing Rly-1 (record mute relay) did the trick, but that uncovered this other problem. Sadly, I've invested many hours in vain here. Part of me wants to salvage my efforts, but the other part of me is saying to move on. At the least, maybe I can disable reverse functions and just set the deck up to record uni-directionally, so at least he can record, even if he has to flip the reels.
I own a 747dbx myself, which I purchased from Japan in April of '84, and I have had nothing but yeoman service from it for all these years, until recently the tension arm belts gave up, so they hunt when there's no tape loaded. Deck still records and plays and meets spec after all these years, too. So when the customer brought in his 747 model (with the LED VU meters), I kind of felt a paternal instinct toward reviving it, if you know what I mean. 🙂
But the harsh environment the 747 has had to endure, plus the all day long play (he said he used it every day since he bought it new in the 80's) wear and tear and the unknown technician repairs (that solder bridge I found was concerning), plus the fact that the customer sprayed cleaning solutions into the FWD/REV sliding switch which probably ruined the nylon/plastic trolley that carries the contacts, all makes me think that further efforts to solve this would be economically absurd.
My initial repair was to fix a 'no record' problem. Replacing Rly-1 (record mute relay) did the trick, but that uncovered this other problem. Sadly, I've invested many hours in vain here. Part of me wants to salvage my efforts, but the other part of me is saying to move on. At the least, maybe I can disable reverse functions and just set the deck up to record uni-directionally, so at least he can record, even if he has to flip the reels.
Hi Mark,
That's exactly what I would be thinking of our positions were reversed. It is also why I suggested you bail on it. The customer knew better when he brought it in for service and didn't tell you. Not nice. I'd charge the guy for the initial repair to fix the listed fault only and release it to him. You fixed his complaint, and he isn't an honest person or he would have warned you beforehand.
-Chris
That's exactly what I would be thinking of our positions were reversed. It is also why I suggested you bail on it. The customer knew better when he brought it in for service and didn't tell you. Not nice. I'd charge the guy for the initial repair to fix the listed fault only and release it to him. You fixed his complaint, and he isn't an honest person or he would have warned you beforehand.
-Chris
30 + years of everyday use in a harsh environment is pretty good service i reckon , not much built these days that'll last that long.
Just a thought but given it's 'home' it probably had copious amounts of WD 40 or similar squirted into it over the years as part of it's 'servicing' 🙂 .... i guess some things have to be let go.
Just a thought but given it's 'home' it probably had copious amounts of WD 40 or similar squirted into it over the years as part of it's 'servicing' 🙂 .... i guess some things have to be let go.
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