Kenwood kr 9940 is GO!

[anderslober]

Ew....ok....this is what fooled me on my qrx9001 project........there was a big discussion going on about bias setting.......the pots on the 9001 had to be at there max. resistance(180 OHMS, I think) for the LOWEST voltage. I then decreased resistance to get my bias voltage UP. This is FOR sure, as I blew 2 outputs the other way around. IE started the adjustment with the trimmer at the least resistance(1 OHM or so).....

Anyway.....it MAY be different on the 9940..........SO, for the lowest STARTING voltage....do the trimmers start at 76 OHM OR 1 OHM setting?

I thought MORE resistance(76 OHM setting) meant LOWER voltage.....................THEN you adjust the trimmer to lower resistance to get the BIAS to 25mV.

 

[EchoWars]

The Sansui and the Kenwood go about adjusting the bias in two completely different ways...the Sansui uses a bias servo transistor. On the Sansui, low bias is achieved with the pot to maximum. The Kenwood is the opposite: low bias achieved with the pot set to minimum.

Can't make generalizations from one piece of gear to another, and certainly not from one manufacturer to another.

 

[anderslober]

EW....NOW that was GOOD info! Ok....so, all manufacturers are NOT the same. Fantastic. I will take care to set the trimmers at there lowest resistance setting(1 OHM) and adjust from there...................on the Kenwood!

I am going on a 10 day trip....so, I wont be able to do it today.......but, I will get back to you..........I will post a few pictures too.

Thanks.

 

[anderslober]

Hello again.....I have been working on the 9940 again.........just finished re-capping the 2 tone boards....that was not so easy....very difficult to get to.......new caps al'round....new relays........ I have checked everything over.........should be ready for power up...........the manual/unit states a 3.5A fuse for 220-240v operation......I only have a 4A fuse at the moment....would it be okay to power up with a 4A fuse? If not......I will get a 3.5A fuse later today or tomorrow.

I will also power ON with vr1-4 set at MIN. as per EW's advice. Then try to adjust BIAS to 25mv across the emitter resistor......should be fun!

Pics when unit is playing!

 

[anderslober]

Got the banged/gunked up kr9940 up and running....it is out of protection, nicely cleaned up and re-capped.........all is re-capped except the large caps.....they tested fine, so I left them alone.

Relays click as they should, tuner works fine and there is sound from all 4 channels.........

A few pics...........

 

[kcollins4]

Good for you! Man, that power supply board sure looks like it's taken some heat in it's lifetime. Glad you got it fixed up.:thmbsp:

 

[anderslober]

It looks ok.......I changed a few resistors and TR's too.

Anyway....I have been testing a bit....only one small thing......the 4 bulbs in the power meters are out....I have pulled them.......and the are fried. Can a 'guru' confirm the voltage(8v?).....the mA is 150. I will need to contact dgwojo........please confirm the above....thanks.
View attachment 262557

View attachment 262558

 

[EchoWars]

Soooo.....measuring the voltage is out of the question because?

FYI, almost all Kenwood and Pioneer 70's gear uses 8V lamps. When in doubt, whip out the DMM.

 

[RichK1]

Lamps

I can't find them in the parts list, but the schematic shows 7 bulbs: 2 for the meters (150 ma) and 5 for the dial (300ma). It looks like they are fed by 7V from the transformer, so 8v lamps should be fine.

 

[anderslober]

richk1.....yes , I figured the 7V from the transformer was maybe the supply voltage....so , 8v/150mA lamps should be ok. There is actually 4 lamps in all.

EW....I didn't want to turn the unit on while it was all apart like above......of course I could, and now will, measure the voltage.......thanks........

Regarding the 'blackened' PS board.....it was in this exact area that the gunk was spilled.....the picture 'lies' a bit......it looks fine.

 

[hatrack71]

What, no front pics? One of the best things about the big Kennys is the face! Show it off dude.

 

[anderslober]

Front will be up soon......just gotta fix the lamps first.............

 

[dgwojo]

Since the globe shaped lamps aren't available anymore, I'd use the 8v/150ma wedge lamps with wires added and 8v/250ma for the dial lamps, Dave.

 

[RichK1]

More Lamps

I know you did not ask about these, but for completeness, the schematic shows the following lamps in addition to the ones mentioned above:

Indicator Lamps:
2CH, RM, SQ, Discrete, CD-4, RADAR, FM Stereo
10v, 50mA

Pointer
5v, 115mA

Question. You note that there are four meter lamps, not two. Which meters get them? I see there are six meters: four VUs (LF, RF, LR, RR) and S and T meters.

Another question: What are RM, SQ, Discrete, CD-4, RADAR?

 

[anderslober]

All lamps are working....except the 4 bulbs in the power meters......1 bulb in each meter. I am waiting for delivery from dgwojo as we speak.........will post, when I get the lamps in.

 

[dgwojo]

Indicator Lamps:
2CH, RM, SQ, Discrete, CD-4, RADAR, FM Stereo
10v, 50mA

Never heard of a 10v/50ma, are you sure it's not an 8v/50ma/4.12mm lamp?? I keep a few 10v/40ma around but never found them used for anything. :scratch2:

 

[RichK1]

dgwojo,

The schematic shows 10v at a point near the lamps, but I did not trace the lines back to see where the power is coming from. Maybe 10v is an open circuit voltage? I have never heard of 10v/50ma either. 8v/50ma is probably correct.
Taking a closer look, the power to the lamps also comes from the 7v taps on the transformer.

anderslober,
I was wondering (for reference), do the T and S meters also have bulbs? If so, are they the same as the four VU meter bulbs? I understand that only for bulbs are dead.

 

[anderslober]

T and S have light. Only the 4 meter bulbs are out.

 

[rBuckner]

Hi

I found this thread while looking for info on the Daiichi relays in a KR-9940 I'm doing. The DC voltage across the coil is about 15Vdc and they are actuated. It could easily be that I have leaking caps or transistors and I plan on a recap of the whole protection board, so it may be that the coil was intended for 24V operation.

My question is: Did you replace the relays and if so did you use the MY2 series relays? Thanks!

 

[rBuckner]

I used the aforementioned relays with sucess, JIC somebody turns this up in a search...