Another d-500 rep

[grapplesaw]

I got a great looking d-500 I bought off eBay last year in broken condition for a $1000. Crazy what these things cost.

So so put on bench and checked out the defective channel so I went to the one without fuses, good guess eh!

After getting low resistance on the output transistors both pos and neg output trans I exposed the back to find two marked with an X on them. It cannot be this easy can it. Well sure enough those were the blowen drivers. Reassemble with good used ones ant test good with high ohm reading across collector and emitter. I also replace the Bias transistor and both channel Zobel caps.

Powered up with DBT and could get only max 45 v with high 6 v DC offset. Tested other channel with all good there.

Next I removed the Q101 and Q107( just different label # than 400 and 500 but same)

powered up , all good, offset voltage good.
Replaced Q101 and Q107 with 2n3440 and 2n5417

repowered again original high dc current. Tested with AP and spectrum analizer and scope

see photos. For a big mess 12 k output.

Diconnected protection with no change.

Now which to change Q102 mps A93, Q106 40412( the big heatsink one) with 2n3439 or the IC.

Anyone got ideas.?? Problem on control board for sure.

 

[grapplesaw]

What next

When powering up left channel through DBT I get light brighten at about 1/2 up the varic
voltage stops increasing as I continue.
Output has about the same DC offset as across the caps (30+ volts) and the AP shows 7 volts AC at about 12 k.

Steps done without any input. Right channel good. Issue is with Left channel only

checked all outputs in place and two differ I've one replace.
Changed bias transistors
changed Zobel cap
changed Q101 and Q107 (note no dc offset or AC output while not in place)
checked both 6,3v 100uf and 100v 47uf caps. (Replaced 100v 47uf as marginal good)
replaced ic lf356 with lf351 ( this allowed higher rail voltage but still 12 k signal high current output
Checked diodes and resistors( resistors not easy to check so did an with same on Right channel)
output as in previous photos

Can this be the Q106 in attached board drawing??

ideas again will welcomed
thanks

 

[grapplesaw]

What is correct output value from Q106 please

Need collector , base and emitter voltages when energized for Q106

Now off DBT

Ok with blue and Violet removed from board
we have high bias of 1 v with minimum setting on vari resistor
1.14 volts at red ( collector ) of bias transistor and collector of Q106
34 micro volts on black ( base)
and next to nothing on brown ( emitter)

 

[grapplesaw]

All good
just needed turn up the wick to over 60 volts rail. Sometime I am to causes
warming up now one channel at a time

 

[grapplesaw]

An other driver blew

With 2.7 volt output I turned the varic up from 150 volts across the cap to toward the high z of240. Around 200 v I blew an other tour put trans next to the one I replaced rarlier. I have pulled it and will retest without replacing it for low output setting but test high voltage.

 

[laatsch55]

Maybe most of those outputs have been stressed.....15024's??

 

[grapplesaw]

High frequency attenuator kicked in

232 volts across the caps 2.8 volts out no heat in anything to speak of .350v bias
and then it happened. Turned off and repowered to 160 volts all is good again. Will rise voltage in a bit. I have spectrum scope on to watch for any thing up to 25k

one should just replace everything to begin with right??

 

[grapplesaw]

Maybe most of those outputs have been stressed.....15024's??

Yes they are Tp9024 1979 vintage

many have dents in the can as in the attached. I see this on many amps. Do people just pound on them? Or is it from overheating?

 

[laatsch55]

Glen , If I have a shorted output and after replacement I get another , they ALL go...

 

[grapplesaw]

Glen , If I have a shorted output and after replacement I get another , they ALL go...

Yes will have a new set in after a little more testing.
As I move the voltage up a little I get a jump in harmonic distortion around 20k. Photo 1is 260volt photo 2 is 195 volt.very interesting. There are no cudgeling caps on the 2n3440 and 3n5317's. I will add now. If no change then a fresh set of drivers are going in.

Any ideas on the dents in the old transistors ?

Edit. Photo 3 has increased harmonic distortion after I backed it down a little

 

[laatsch55]

Yes they are Tp9024 1979 vintage

many have dents in the can as in the attached. I see this on many amps. Do people just pound on them? Or is it from overheating?

Damned if I know, never seen that...

 

[grapplesaw]

Yes will have a new set in after a little more testing.
As I move the voltage up a little I get a jump in harmonic distortion around 20k. Photo 1is 260volt photo 2 is 195 volt.very interesting. There are no cudgeling caps on the 2n3440 and 3n5317's. I will add now. If no change then a fresh set of drivers are going in.

Any ideas on the dents in the old transistors ?

Edit. Photo 3 has increased harmonic distortion after I backed it down a little

Photos are now loaded

 

[laatsch55]

Yes will have a new set in after a little more testing.
As I move the voltage up a little I get a jump in harmonic distortion around 20k. Photo 1is 260volt photo 2 is 195 volt.very interesting. There are no cudgeling caps on the 2n3440 and 3n5317's. I will add now. If no change then a fresh set of drivers are going in.

Any ideas on the dents in the old transistors ?

Edit. Photo 3 has increased harmonic distortion after I backed it down a little

So the big register is the freq your having a big jump in distortion?

 

[grapplesaw]

So the big register is the freq your having a big jump in distortion?

Not to sure what to make of it.

I was hoping to just patch this puppy. Rather than screwing around any more I will give it a good upgrade
New mj21196 outputs with original 410's
add caps to cushion the 2n3440s
replace other ic with lf351
replace power resistors with 7.5k
new bridge rectifier with snubber caps

 

[laatsch55]

Didn't you have any 3439's??

 

[grapplesaw]

Didn't you have any 3439's??

Yes and will use them along with their mate. Also new power caps , I am considering Nippon 22,000uf 200v large can.

 

[laatsch55]

200 volters are pretty big caps...

 

[grapplesaw]

Big Caps

200 volters are pretty big caps...

That is the point Lee bigger is better right? Actually these are 3" x 5-1/8" tall. The originals in the 500 are 125 volt 12,000uf large can 3" x 5-5/8" tall. So going to 22,000 200v is not a push. Will have to scope the supply when installed to make sure it is smooth enough. I found some used 33,000 uf x 150volt caps for the monster mono. How does four off those sound with the two transformers from Perry?

 

[laatsch55]

Sounds good to me...

 

[oldphaser]

Yes they are Tp9024 1979 vintage

many have dents in the can as in the attached. I see this on many amps. Do people just pound on them? Or is it from overheating?

Glen,

The dents in the TP9054's is common place in the D-500's. Someone at the factory must have used a pair of needle nose pliers or a screw-driver to install them. The transistor leads barely push through the sockets so they must have wanted to make sure they were in as far as they could push them. They must have figured that the dents would hardly be noticeable behind the perforated screens on the heat-sinks.

Ed