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The
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Path: /yihua/853d/

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Redrawn Zeny-Yihua 853D PS

The 853D I acquired had Variable power supply problems–The SMD & soldering functions work fine. I really don’t use the PS on this unit but knew it had a problem so decided to tackle it. I googled to try & find a schematic for this unit & found what info Steve K7LZJ had put out there on the BAMA (Boat Anchor Manual Archive) site which included a schematic.

I found the TIP3055 pass xtor was shorted C to E. R28 .27 ohm 3 watt resistor increased in value to approx. 30 ohms. I replaced the bad components & got the supply to work somewhat— The power supply display would blink on & off at approx. a 1sec intervals but I was able to see that the supply was changing values with the Volt Adj.pot. Going back to the schematic I see that Q6 a switch that is connected to pin 13 of the LM723 IC this is the Freq Comp, pin but but can also be used to enable or disable the 723. The base of Q6 is connected through R32 10K ohm resistor to pin 1 of con12 this cable is connected to the display board on the front of the unit which there is no schematic for. A positive voltage on pin 1 will cause Q6 to conduct & shut down the LM723. I unplugged the con 12 cable from the PS board & the power supply came up & operates normally. For me this is a fix for now–more research needs to be done to understand how all of the functions on this unit works. The PS schematic Steve provided is of the power supply only–there nothing on the solder/SMD functions circuitry.

I redrew Steve’s hand drawn schematic to make it easier to read. On other files here at BAMA Steve talks about what a weird design this PS is & I agree with him totally. The heat sink is way too small for higher currents which in my case (and probably many others)caused the 3055 xtor to fail. I noticed on the rear portion of the chassis there are holes punched into it for mounting a TO3 transistor— say 2N3055 or 2N3771 which would work much better than what came with the unit & allow higher currents to be drawn from the supply.

Well this is my story & I hope this info will be helpful to some people in the future as I found some guys on different blogs asking questions without getting answers. There was also a website I found that has info on this topic that appears to have been hacked—the written portion of the info appears to be somewhat helpful but the schematics have been replaced by audio equipment schematics.

Ken
K9KO

Files:

Redrawn Zeny-Yihua 853D PS.pdf
(330 KB)
Yihua_853d_3N1_manual.pdf
(1.2 MB)
Zeny_853D_adjustment_and_power_supply_upgrade_pix.pdf
(330 KB)
Zeny_853D_manual.pdf
(2.5 MB)
Zeny_853D_MB_parts.pdf
(55 KB)
Zeny_853D_MB_parts.xls
(36 KB)
Zeny_853D_schematic.pdf
(780 KB)