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Technics SH 8066 display problem

Gigiga

Gigiga

New Member
Hello guys. I have another problem with my Technics SH 8066 equalizer that I can't solve. For a few days, when I turn it on, all the LEDs on the front light up at the same time, for a few moments only, and then return to normal (that is, only those above the keys used last time remain lit) while the audio spectrum display shows a strange lighting (see photo 2). After opening the device, I replaced all 9 electrolytic capacitors in the power supply area and the two 3.3 F supercapacitors (one was visibly deteriorated) but without success. Has anyone had the same problem with this equalizer and, if so, how did you solve it? Thanks and greetings to everyone.
 

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I've never worked on anything like this but the problem does not seem like it is the kind you would see as a result of a power supply issue.

Does the unit sound OK? Does it behave normally except for the display?

Without schematics it is very difficult to give any real direction but the first things I would look for are display driver chips.
 
i had some ghosting in jvc flourescent meters and there were some bad caps in the meter driver circuitry

but that would not explain all the front panel leds lighting up on powerup. that would be a separate led driver circuit.

there's a free service manual online.
 
The equalizer works regularly in all respects. I also downloaded the service manual but, unfortunately, I was unable to obtain any useful information. At first I thought it was a problem deriving from poor power supply (for this reason I wanted to change all the capacitors in the power section) but not solving it and not finding anything on the net about it, I do not know what else to do.
 
Gigiga said:
I was unable to obtain any useful information.
Click to expand...


the block diagram basically points you in the areas to look.

the schematic shows you the components in those areas with voltages even.

it's pretty complex and it may or may not be repairable but the manual is excellent.
 
True. Unfortunately I am not a technician in the strict sense: since the service laboratories in my area no longer accept these devices, due to lack of specific knowledge or spare parts, I am forced to do everything myself. Unfortunately I still cannot read/understand the electrical diagrams correctly and I have no friends who can help me in this sense.
 
Gigiga said:

hfe_technics_sh-8066_service_en.pdf

drive.google.com drive.google.com
Click to expand...

Excellent! I took a very brief look and there is a LOT of information there.
I'm happy to go over this and see what I think but it may take me a day or two. perhaps some others will look and chime in as well.

How experienced are you at electronics troubleshooting and repair? What if any test equipment do you have. What about repair stuff like a soldering iron just in case?
 
For some years, driven by necessity, I have been trying to repair the faults of my old hi-fi equipment by following the information I can find on the net. Not having sufficient technical culture, I do not own an oscilloscope or even an infrared or hot air soldering station (whose costs would be excessive for my frequency of use). I have, in addition to the classic electric soldering iron with thermal tip, a desoldering station with gun, another "pliers" desoldering iron specific for electrolytic smd capacitors and a digital reading tester.
 
I replaced all the electrolytic capacitors (including C16) in the power supply quadrant and the two twin rectifier diodes D13 and D2. I was unsuccessful: the problem persists even after these replacements.
 
Did you do any measurements? Display ghosting usually (but not always) is caused by bad voltage values. The cathode should be at -24 V, the grids at -31 V for the segments to be dark when not selected. The voltages are in the schematic (glued version just uploaded at Miss Tanya's). Sometimes the display drivers (in the micro IC60) go phut. That would be a problem.

As for the weird startup, this is usually (again, not always) caused by an upset micro. Check reset circuit (Q703/4, IC60 pin#49).
 
@ PE9ZZ I downloaded the diagram you provided, and if I've interpreted the wiring correctly (unfortunately, I'm not a technician), the pin that supplies power to the fluorescent display is J8, which, according to the diagram, should provide 5 V to pin 2 and -24 V to pin 4. When powering the equalizer, I detected a value of 4.9 V on pin 2 with the tester, and a value of -29.5 V on pin 4. At this point, if the nominal ratings are 5 and -24 V, pin 4 incorrectly outputs -29.5 V, and this (I believe) explains the ghosting on the display (which wouldn't turn off completely due to the incorrect voltage). Now the question is: if that's the case, what's causing the voltage on pin 4 to be incorrect? I've already replaced all the electrolytic capacitors and the two rectifier diodes on the "power supply" dial.
 
I measured the 6.8 V zener diode D17 both soldered onto the board and off the board: in both cases, the tester's display, in "diode test" mode, shows a value of "1046" from cathode to anode and "1" when reversing the probes (for my tester, 1 is equivalent to OL on other devices, I believe). I repeat, unfortunately, I don't have a technical background, but from what I've read around, it seems to be a non-standard value for a zener diode (I've read ranges from 0.5 to 0.8) even if you respect the direction of current flow (which would suggest the diode is good). In practice, does this value of 1046 indicate whether the diode is good or not?
 
Gigiga said:
In practice, does this value of 1046 indicate whether the diode is good or not?
Click to expand...
I don't have the foggiest. This how you can test it. Clip your test leads to both ends of the diode. Take a resistor of 1k and a 6F22 (9 V) battery. Or a power supply. Connect it via the resistor (does not matter which lead or which way around). With the plus connected to the band side of the diode your meter should show around 7 V, the other way around 0.6 V. If it does that it is not borked. But based on your measurements I think it is.
 
I have some Technics cd players and they light up all segments of the 7 segments display on ipo. It's a feature not a problem.
 
No success! After replacing the original zener diode (MA4068) with a new one, I also replaced the Q715 transistor (2SA1310-T), even though the original appeared fine under the tester. The ghosting on the spectrum analyzer remained the same, as did the anomalous lighting of all the LEDs on the front every time I turned it on. I wasted time and effort for nothing. At this point I suspect that the fault lies with the integrated circuit IC 60 (coded HD614042SB22)...which is no longer found.
 
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