• The move to the new server is done. There are some software and database maintenance updates in process. This has us passing the hat around to help out. We appreciate any donations. Seriously, even a dollar helps. The payment page may be found here - https://www.audiokarma.org/support.html

SX-1010 tuner

Well, they sure ain't gonna be at Radio Shack...

mouser.com 512-UF4004 @ $0.12 ea

400v 1 amp (1.0v forward drop at 1 amp, 0.5v at microamp levels)
 
OK- D7 and D8 should be replaced with 2each(A-frame) Uf4004 diodes? Should i repeat this process on the other amp board as well? The channel that has the bad diode (D7 STV-3)is the channel hooked to pin 3 on the protection circuit. (-3v:+5V) causing the relay to cut out.
Ordered 12 UF4004 diodes just in case
 
Maddart said:
OK- D7 and D8 should be replaced with 2each(A-frame) Uf4004 diodes? Should i repeat this process on the other amp board as well? The channel that has the bad diode (D7 STV-3)is the channel hooked to pin 3 on the protection circuit. (-3v:+5V) causing the relay to cut out.
Ordered 12 UF4004 diodes just in case
Click to expand...

Looks like a smoking gun to me....

Taking a step back for a minute....

The protection relay would open and close, The protection circuit's probable weaknesses were eliminated by changing out electrolytic caps and the relay driver transistor Q7. The protection relay STILL continued it's antics.

Then we discovered the pin 3 protection circuit voltage variations that were in sync with the relay's antics.

Then the replacement of electrolytic caps and two suspect transistors on each (for symmetry) amplifier channel was started as a shotgun repair for an intermittent fault.

On what we now recognize as the right amplifier channel which feeds pin 3 of the protection circuit we found a defective, probably shorted (and intermittent) stv-3 diode. Replacement of it (and it's brother on the other power supply polarity) is anticipated with a pair of UF4004 diodes EACH...

So hopefully that is the end of the protection relay's antics.

BUT:

The sound would go away on FM (did we ever distinguish the loss of FM sound independent of the protection relay's antics?).


As for the dual UF4004 diodes, the right channel definitely, the left channel, yes... for symmetry. save the stv-3's...
 
MTF

You are absolutely correct.

We never did pin down a cause for the loss of the tuner FM and AM. I assume it is the pwr. supply which I have all the caps to rebuild the power supply circuit.

We went after the protection circuit problem first, replaced the caps and Q7 if i'm not mistaken. ZTX1056a sounds right.

The problem continued which then led us to the amp boards.Currently under reconstruction,and hopefully the solution to the relay problem.(Keeping fingers crossed)

We didn't find out what caused the D7 to short or what caused the blackening (looks like shorting) on the foil side shown in pervious photos

Thanks
Mark
 
Maddart said:
We never did pin down a cause for the loss of the tuner FM and AM. I assume it is the pwr. supply which I have all the caps to rebuild the power supply circuit.
Click to expand...

The only time I have seen a tuner periodically loose output was an AM tuner using an HA1197 chip when it was run near 15 volts.

Otherwise the tuner power has to disappear, something that is very easy to check. Of course we have to get the amps back up to get power on first.

Recapping the power supply isn't a priority since you reported the voltages are close to what the schematic calls for, as long as the voltages are stable.
 
The SX-1010 has the dreaded upside-down regulator that bakes all the components on it...there's a good possibility that most of the small electrolytics on that board are as dry as a popcorn fart.

This may not be immediately relevent to the problem at hand, but if you have to tear into the regulator, recap it.

If/when you attempt this, capacitor height is an issue. The heatsink is a guide as to how tall any one cap can be, as it barely clears the bottom panel (and is also why you see so many SX-1010's with cracked regulator boards...a good hard shot to the center of the bottom panel will do it). The only five caps where this may be an issue are the two 2200uf 10V caps, the two 470uf 80V caps, and the single 1000uf 35V cap. I use the Panasonic FM caps (#P12357-ND, Digikey) for the 2200uf 10V caps, the Panasonic TSHA snap-in 820uf 80V caps (#P7496-ND) to replace the 470uf 80V caps, and a 1500uf 35V TSHA snap-in (#P7465-ND) to replace the 1000uf 35V cap. I can't quite remember, but it might be necessary to open up the holes for the leads of the snap-in caps, as they may be slightly larger than the originals.
 
I don't know what the voltages are on the PS when the tuner actually cuts out. The voltages i measured is with the tuner operating. Below is the list of caps i have to perform the PS recap. Probably a few extras in this list.
Digi-key#
4-p10323-nd 100uf/50v
1-p11198-nd 100uf/16v
2-p10321-nd 47uf/50v
1-p10246-nd 330uf/16v
1-493-1808-nd 4.7uf/25v
4-493-1985-nd 470uf/100v
2-p10271-nd 220uf/25v
4-p10285-nd 2200uf/25v
4-p10775-nd 100uf/100v
2-p10333-nd 1000uf/50v
 
Just received the diodes. Soldered them into a frames. I assume that the band on the diode will go to the cathode end shown in the symbol in the photo. (Actually that same symbol that is printed on the Pcb)
 
Maddart said:
Just received the diodes. Soldered them into a frames. I assume that the band on the diode will go to the cathode end shown in the symbol in the photo. (Actually that same symbol that is printed on the Pcb)
Click to expand...

Yes, correct.

As I mentioned before, once the amplifiers are back together (and installed) some checks will be necessary. IF the power output transistors haven't been disturbed, it won't be necessary to test for shorts of all the leads to the heatsinks, although a visual check (with light pressure on the wire to be sure it's secure) for broken wires would be prudent.

Basically the idea will be to do ohmmeter checks for zero ohms between the actual leads of the components that are supposed to be connected with something offboard as well as the critical bias current loop.

The bias pots should be cranked down to zero ohms initially, then adjusted upwards, since we DID change some of the bias circuit transistors.
 
Both Amp boards are back together with the "A" frame diodes (.92v:.98v/OL) and stv-3Hs are mounted back to the heat sinks.
:banana:
STV3H Left-1.434v/OL
STV3H right 1.365v/OL

The output transistors with heat sink were lifted out and over the amp board to allow for access. Visually inspected wires all look well.
:banana:
 
Maddart said:
Both Amp boards are back together with the "A" frame diodes (.92v:.98v/OL) and stv-3Hs are mounted back to the heat sinks.
:banana:
STV3H Left-1.434v/OL
STV3H right 1.365v/OL

The output transistors with heat sink were lifted out and over the amp board to allow for access. Visually inspected wires all look well.
:banana:
Click to expand...

What do the other stv-3h diodes on the pc board's heatsink measure at?
I checked an stv-3h here at 1.48v. I was worried that 1.434 was too high, compared to the 1.365v until I checked one here. Lower voltage isn't as much of a problem as too high..
 
What do the other stv-3h diodes on the pc board's heatsink measure at?

L=1.445v
R=1.426v

The stv3h mounted on the output heatsink(Large ones) could be replaced with 3 uf4004 diodes in series? Just thinking that the exhisting setup is a fragile one and the stv3h isn't a thermal device so why mount to heat sinks?
 
Au contraire...the STV-3H is very much a thermal device (as are all semiconductors).* Without it being mounted on the heatsink, thermal runaway (and the inevitable destruction of the output stage) is imminent.

The STV-3H devices are a PITA to locate, but it can be done. It's the STV-4H which is Über-rare. Don't even think about replacing one unless you've killed it somehow.

*Connect your meter to read diode voltage drop on one of the STV devices. Now hold your fingers on the diode to impart some body heat to it, and watch the voltage necessary to overcome the depletion layer junctions drop. Remove you fingers, and blow on the diode to cool it off, and watch the voltage rise. Now tell me it isn't a thermal device. :yes:
 
Ok i stand corrected.
I thought that a thermistor was the only thermal component.(that i am aware of). Is the STV-3H a varistor?

Mark

I am ready to start testing the Amp boards if you have a procedure. Hope to avoid meltdown and keeping fingers crossed this stops the relay from kicking out
 
The tests were mainly to be sure that the bias diodes on the main heatsinks had unbroken circuits from VR2 through D5 , D6 and finally Q5's collector. The only source of problems in this case would be broken wires, probably on D5 and D6, so with the measurements you made on all four STV-3H diodes , if they were made from the solder joints on the pc boards, would suffice.

The problem that happened, in a past thread, way back, was that VR2 had been burned up and the circuit broken so when the power was applied, the outputs all blew up.

Since this amp was working, You just need to read the resistance between the collector lead of Q4 and the anode lead of D5 the stv-3h diode mounted on the heatsink that is mounted on the PC board. Zero ohms is correct, because a new Q5 was installed.

Q6 is the STV-3H diode on the other heatsink, the one with the power output transistors mounted on it.

You want to see zero ohms from D5's cathode to D6's anode.

You want to see zero ohms from D6's cathode to Q5's collector.

Since Q5 was replaced, when the amp is turned on, watch outfor the output heatsinks getting hot.

Then:
measure between Q4's collector and R23 for +1.8 volts or so
measure between Q5's collector and R24 for -1.8 volts or so
If you don't see about these voltages, shut it down.

IF the voltages are good, VR2 is adjusted to get the bias current to 12.5 millivolts across the 0.5 ohm resistors between the amplifier outputs and the output transistor emitters (r29, R30, R31 & R32).

The manual does NOT specify the procedure for doing so, but you slowly turn it up, and let it stablilize for 20-30 minutes and then re-check it. There is NO sound coming through for this setting.

There are four resistors per channel and there will be four readings, and it is important to see how close those readings are. IF any one reading is above 30 (from a good 12.5) SHUT IT DOWN. This is the blance of power sharing between the output transistors.

It IS possible that the setting necessary to get a reading of 12.5 on any particular one MAY put the other set of output transistors in jepoardy.
 
Mark
There are four resistors per channel and there will be four readings, and it is important to see how close those readings are. IF any one reading is above 30 (from a good 12.5) SHUT IT DOWN.
This is the blance of power sharing between the output transistorsIt IS possible that the setting necessary to get a reading of 12.5 on any particular one MAY put the other set of output transistors in jepoardy..
Click to expand...


While i'm very good at following instruction (Been married a long time) and your instructions are very detailed, I believe it would be in the best interest of the sx1010 to have a pro take it from here.
Again trying to avoid meltdown.
If you could PM me i would like to drop it off after the holidays.
I also have the parts to replace the caps on the PS, I could replace those now or it could be done when its with you. Also should i leave the covers off or button it up?
 
Maddart said:
Mark



While i'm very good at following instruction (Been married a long time) and your instructions are very detailed, I believe it would be in the best interest of the sx1010 to have a pro take it from here.
Again trying to avoid meltdown.
If you could PM me i would like to drop it off after the holidays.
I also have the parts to replace the caps on the PS, I could replace those now or it could be done when its with you. Also should i leave the covers off or button it up?
Click to expand...

It's safer to button it up just like original, remove the fuse & put it in a baggie inside so power isn't applied.

As much as it pains me to say it, don't do the power supply caps before the amp is back running... sorting BOTH out at the same time gets into a chicken/egg situation, even though I'd rather you did the power supply caps.

And dropoff asap before holidays is welcomed... I have 4 units I'm working on right now that the parts won't get in until the end of next week so something with parts could slip in and out without a ripple.... but traveling today is dangerously icy - my Sunday company prudently stayed off the roads today.

BTW: powering up from zero bias isn't that bad, the first thing I check is the + and - voltages I mentioned, repeating for the other channel. then at zero bias I check that the dc offset is low (and adjust it to zero), repeating for the other channel. Then I check the 4 resistor's voltage readings for low or zero indications on each channel. Then one channel at a time I just turn the bias up a little bit at a time and repeat the 4 readings looking for any that are jumping ahead of each other (if they want to it will be quickly apparent), turn it a bit more, repeat etc.... it's not rocket science....
 
Mark
I sent a PM. Can probably sneak away from work monday at lunch time providing the weather isn't too bad. Let me know if this is acceptable.
Thanks
 
Yes, It's fine... but it IS a ways away from Lisle.... Gimme a holler if you're on the way....
 
It's here ... amp has been powered up sucessfully. Power supply voltages good.

Has NOT gone into protection for several hours of FM operation.

NICE job on the amps and protection boards.
 
You must log in or register to reply here.
Back
Top Bottom