i have an '87 sony jh24 that is stuck in some sort of edit tension
wind, supply going clockwise, take-up counter, they look like they are
travelling the same speed, sort of 15 ips-ish. all transport controls
are unresponsive. my tech socketed as many ic's on the logic board as
possible, they seem to check out. the switches are good. the edit
light is stuck on, and the syptoms are same whether auto locate is
connected or not.
Thanks for your time.
Mike Brannan

In article ,
mbrannan wrote:
i have an '87 sony jh24 that is stuck in some sort of edit tension
wind, supply going clockwise, take-up counter, they look like they are
travelling the same speed, sort of 15 ips-ish. all transport controls
are unresponsive. my tech socketed as many ic's on the logic board as
possible, they seem to check out. the switches are good. the edit
light is stuck on, and the syptoms are same whether auto locate is
connected or not.

Do you have the remote unit?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

The first order of business is to power down the machine,remove each
transport card from the motherboard, replace it, then power up. Same with
the voltage regulator at the extreme left of the m.b., it looks like a power
transistor. Same with the small cards along the top of the m.b. Find the
problem yet? Sooner or later, all those molex connectors need to be cleaned
and stabilized...

....Paul

--
************************************************** ********
"In the analog realm, it ain't "OVER" 'til it's over."

"mbrannan" wrote in message
m...
i have an '87 sony jh24 that is stuck in some sort of edit tension
wind, supply going clockwise, take-up counter, they look like they are
travelling the same speed, sort of 15 ips-ish. all transport controls
are unresponsive. my tech socketed as many ic's on the logic board as
possible, they seem to check out. the switches are good. the edit
light is stuck on, and the syptoms are same whether auto locate is
connected or not.
Thanks for your time.
Mike Brannan

Thanks for the info Paul, I pulled them already and my next order of
business is to check power supply rails on the transport supply. The
logic supply is good however. Here is a message that relates that I
posted up on sci.electronics.design. Maybe this might help to shed
some light as well.
************************************************** *******************************
Hi All...

I've got a rather odd problem with a Sony JH-24 24 track tape deck
transport. The control circuitry is quite simple and based on
straight 7400 series TTL. Each of the functions for the unit, i.e.
play, stop, rec, etc. are operated from a respective momentary switch
that is grounded at it's pole and then ties to the control board
through a 4700ohm resistor. Each of the functions are the same switch
circuit up to the control board, so I'll just describe only one. When
the switch signal enters the control board, it is tied to it's section
of logic inputs be it a 7408, 7420, 7400 gates. Also on these inputs,
there is a pair of 1N4004 diodes tied together on one end to the
signal input to the gate and are tied on the other ends, reverse
biased, one to the power supply and the other to ground. See the
following URL for a schematic:

http://www.thesonicfrog.com/logic1.jpg

Now, what's happening is that when I just take a measurement of the
input to the gate when I push the control switch, I see a +5V turn to
+1.5V. Now, that's certainly not enough to be considered a logic 0 as
the margin on the low side is 0.8V, right? This characteristic is
showing up all over this control board. And I believe it to be the
reason why this machine is completely inoperable. But, my gut is
telling me that there is something else going on here because the
chances of a system wide failure of this many gates is astronomical.
Also, I have removed all of them and tested them individually out of
circuit. I've installed sockets and have changed the different gates
to 74F logic and I find that some of the logic functions now somewhat
work, but still this isn't curing the problem. I suspect that the 74F
is a little more forgiving of the sort of dead zone between .8 and 2V
that the control switches are generating. So, I guess my question is
this... do the inputs to straight 7400 series when tied through diodes
as I said and unterminated on the switch ends when one is not
depressed, normally float like I'm describing? What would be causing
the 1.5V levels that I'm reading? One could guess the diodes leaking,
but there are 4004s and I highly doubt so many of them would be
experiencing the same problem. Any ideas?

Thanks for any suggestion.
Dan
Dan Charette }
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