Technics SH 8066 display problem
- Thread starter Gigiga
- Start date
this is a rabbit hole that i have gone down and i am not very experienced but i can share some of what i have learned
this is the part number - HD614042S
this code here- b22 could be either a date code or it could be a manufacturer specific code(meaning that hitachi could have altered their base model for an extra feature that panasonic required)
find someone that stocks the base model and call them or email them and see if someone can help you further.
like these guys. there might be a language barrier involved so be warned
HD614042S Hitachi Microcontroller Reliable Electronic components - Tech-Electr
Microcontroller, 4-Bit, MROM, HMCS400 CPU, 0.56MHz, CMOS, PDIP64
tech-electr.com
if you were to replace this, i would try to find a socket for it rather than solder it directly.
for $20, it might be worth a shot IF you KNOW that is the problem. but 20bux here and 20bux there starts to add up quickly.
i don't know that i would personally pursue this myself but good luck to you if you do.
i was afraid that might be the case but was not 100% sure.
in google chrome you can right click that page and translate it.
From the grid outputs to -31 V. The grid outputs on your IC60 are 1G to 13G on your FL display. If you look at it, you see 1G go to R51, which is pin#25 on IC60. The pins that need that pull-down resistor are even marked "Grid" on IC60. So each Grid pin should get its own 100k resistor. The other ends all go to the -31 V rail. Prolly best location is emitter of Q715 because there is some switching going on. Display blanking or somesuch. Try one resistor first to see if it helps. If it does plonk in the other 12.
Gigiga
New Member
Forgive the incompetent question but... looking at the diagram I see (if I interpret it correctly) that from transistor Q715 a voltage of -30.5 V reaches the anode of the zener diode D17 while from the cathode it should come out -24 V. Couldn't I replace the 6.8 V D17 with a different diode (I don't know what voltage) in order to bring the output voltage from pin 4 of J8 from the current -29.5 V to -24 V?
You're forgiven. No, you cannot because the 6V8 zener sets the cathode voltage on the VFD. If the cathode voltage is identical to grid voltage all segments will light up just like they do now.
Oh, crap... I just realized something. Good thing you asked your incompetent question because I just realized that it's not the grids that should be pulled down but the segments. The schematic has some nice scope images next to IC60 showing the levels you should see at the terminals of the VFD (or IC60). If you do that too you will see that the segments do not go down to -22 V. This sucks electrons from the cathode to them causing the ghosting effect. Pulling down the grid lines likely does nothing.
No, you just have to pull down the segment lines instead of the grid lines. And see if that solves the issue. If you have a scope you can observe the effect.
eXpediency
New Member
In my SH-8066, a revision of the soldering of the C16 contacts and the pad on the board helped.
If the diode does not have a connection with C16, then only a rectified semi-sine wave will pass into the circuit...
For the entire circuit -31.3V Led Driver
.If, of course, your +5V logic control is functioning properly.
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Gigiga
New Member
Did you have the same problem of ghosting on the display and LEDs on the keys? I also replaced the 6.8V D17 zener diode but even after replacement the problem remained. Now I measure a voltage of -32.5 V on the anode of the D17 and -25.7 V on the cathode. Testing the J8 connector (the one that powers the display) with the device turned on and the plug inserted, I measure a voltage of 4.8 V on pin 2 and -25.7 V on pin 4. Now remeasured the voltages on D13, finding -33.9 V on the anode and 0.0 V on the cathode. On D2, I measured 0.0 V on the anode and +12.9 V on the cathode.
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eXpediency
New Member
eXpediency
New Member
Owning 80's era technology requires some technical knowledge. Since there is almost no service from the manufacturer at all.
You need to find out dU as DC(~5V) - the ripple range at C16/D13 and AC(-31.3V)
It would be more informative to look at point C16/D13 with an oscilloscope...
For Led Drive, voltages are generated from this point.
If there is a problem in it, then further in the scheme it will not be better.
Or somewhere here (minus C711 cathode Q715) , tuck in an electrolyte, like C16.
Observe polarity. Plus on the ground point.
That's right.
For this reason, I came to this topic in search of a solution.
Before this, I inspected the LED SOURCE on the front panel (It went out spontaneously after switching on. Soldering the contacts solved the problem.)
eXpediency
New Member
I'm the same.
The LED only requires soldering connection points on the board.
C16 has a seizure with a capacity check.
About soldering and cleaning the contact points on the board and its reassembly C16.
Particular attention was paid to + contact C16, which is to ground.
Electronics is the science of contacts.
It is not there or it is where it should not be.
Gigiga
New Member
No luck! I've re-hardened all the LED and connector pins on the front board, desoldered C16 (50V 220uF), cleaned the leads thoroughly with isopropyl alcohol, and soldered a new capacitor. Unfortunately, the problems persist. I even replaced the 6.8V zener diode D17 with an 8.2V one in an attempt to "dope" the voltage at pin 4 of J8 from -25.7V to -24.3V (much closer and within tolerance of the -24V specified in the service manual), but, damn it, I now get a voltage of -21.8V, and the ghosting on the display has remained unchanged. I think I'll have to face the facts and keep it as is. Aside from these two issues, the equalizer still works properly.
Did you ever try those pull-down resistors for the segments? Real quick 'n' easy to test with one segment.
Gigiga
New Member
No, I've never tried because, unfortunately, I don't have the technical knowledge or the proper equipment to do so. Despite my ignorance, I'm convinced the VFD isn't dead (the defect suddenly appeared a year ago and has remained unchanged since then, without deteriorating further) but rather there's some damned faulty component somewhere, on the motherboard or the front panel, that's sending incorrect voltages to the keyboard and display. The problem is, I can't find it on my own.