Restoration HP8662A

2020/5/30

HP8662A is a remarkable synthesized signal generator. Get one HP8662 is kind of lucky. Even though It's not in perfect status,  It still could power on, every key is reponsed. Of Course, the status blink, showed 99 error code. 

Reference manual stats the code 99 means hardware malfunction, consult the blue key for sub status code,  It's say 02.  I do a initial cleanup, ie, clean the top/bottom and side cover, clean up dust where I could reach for now.

Power Failed

To locate what the sub error code 02 means, Open the top cover, power on the machines.  I see servarls red LEDs light. What a bravo design , so easy to locate error code, each LED associated with a number. 

There are more that one red led light up. It's easy to notice the root problem is -10V is down(A7A1), so every modules need -10V is also down.

I then pull out module A7A1 and replace several electrolytic capacitor, and also curisioly pull out A7A2, A7A3, clean dust and re-inserted.  Then a series disaster began.  It must be the A7A2 control board which not inserted properly -- half inserted.  And the inverter switch transistor base limited fuse is blow up, and so did the line power fuse.

I can't remember what exactly happens. Checking invert board then,   Q3,Q4 is gone, switch drive transistor Q1,Q2, the 2N3867 also died.  No wonder why it blow up fuse repeatedly. One 2N3867's bias resistor exploded into pieces. There must be some serious error happened to it. 

A half working HP8662 totally dead now. Man!

Cleaning

Don't be panic.  It's good time to clean it up. Starting form the A7A1,A7A2,A7A3, A7A4, the whole power supply.

After cleaning up, It  begin to glowing. The computer boards is another easy task. The motherboard is hard to disassemble, I leave it to another fun project.

Power Supply  Parts Replacements

Most of the parts, the transistor especially, is TO-39 and TO-220 metal can,  they are not easy to find, then need replacement. Let starting from the high side, the inverter, A7A3.  This board hold +- 160V switch transistor Q3, Q4, and driver Q1,Q2. Other parts on board is transformer and inductors. 

Power switch Transistor 

Unlucy, I do  not find the Q3, Q4 cross reference model.  HP 1854-0657  is used for other HP device( HP 62600 J series power supplies).  On board transistor marked with RCA, but no specific parts number. 

It's hard to identify what is the HP 1854-0657. I located a HP63005C/63315D module power supply, which also mark it's switch transistor as HP1854-0657, and , it's 2N6306.   HP-63005C-63315D.  They are not toltally identical but share same HP parts number.

HP8662 reference manual state the Q3 Q4 drive current is 0.35 mA, HP662A power consumtion less than 420VA, maximum current on switch inverter(160V) is 450VA/160V ~=  2.8 Amp.

2N6306  Hfe > 15,   350 mA should be well enough drive it to saturation, 0.35x15v = 5A.  Seems could be a replacement. 2n6306 And Replacement  (Vceo 

There is another transistor 2N5240 , seem much better match the original transistor marked RCA. RCA produced 2N5240 ,  100W 5A, 300V  Hfe>20  switch transistor. 

HP8662 marked the 1854-0657 is a 75 Watt transistor.  (BUX48 might overkill)

Inverter Switch driver

Q1,Q2  is  HP 1853-0442     2N3867(PNP), this tansistor had a very good replacement, 2SA772. 

Q1-3:  1854-0846   2N5878 (on board) : replacement 2N6340/41 , 2N6686( much high power)

1826-0016  LM204

1826-0473   

1820-0247  LM305