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Refurbishing Denon Direct Drive TTs

MonkeyRelish said:
Non temperature compensated zener diodes maybe ?

Mr Relish
Click to expand...
The circuit around the reg's was supposed to help stabilize things, I had suggested a mod that eliminated the zener shunt ckt and subbed a series pass 9V monolithic IC regulator that worked well in the previous case. It's in a past thread in AK turntables somewhere.
 
Pio1980 said:
The circuit around the reg's was supposed to help stabilize things, I had suggested a mod that eliminated the zener shunt ckt and subbed a series pass 9V monolithic IC regulator that worked well in the previous case. It's in a past thread in AK turntables somewhere.
Click to expand...
This is getting annoying. I found a suspect wire, fixed it no change, tested the Zeners all good. Tested much of the silicone, some in situ, others looked no good, then you go to the trouble to test out of circuit an all good.
I found a circuit on VE and one of the caps the previous owner had changed he had connected two 100uf caps together to get 200uf when the board value should have been 220uf. Problem is bodge only measured 175uf so I was hopeful, but correct cap and still no change. Over the holiday I will check if he has made anymore stuff ups. Starting to run out of ideas now though..
It starts off stable, then after maybe 2 minutes it starts to go slow so you adjust, then it is good for a minute, then goes fast so you are back where you started. Head is adjusted correctly. I have even checked the motor all good. This HAS to be a dodgy cap or leaking silicone but just not finding it.
Chris
 
Wow what the previous owner doing!! C1 is supposed to be 0.22 UF 25v he has 0.47 100v
c4 not so bad 100uf 25v is substituted for the same with 100v
c5 is nuts 1uf 50v has been replaced with 10uf 160v!!!
c7 10uf 25v replaced with10uf 160v not ideal but ok I suppose
c12 100uf 25v replaced with same 100v, again ok
another curly one c19 1uf 50v replaced with 10uf 160v!!!
I dont think this is the issue but really not going to help!!
Need to see what caps I have, hopefully I can improve this.
Chris
 
Started tracing out what he has done, near the pots tracks are gone and he has redone it so hard to know what was where. Anyway so far so good all is SO FAR connected to what it should be.
Tomorrow I will check all the resistors, maybe one is going bad and drifting as it gets hot. Fingers crossed..
Chris
 
Does this model have a crystal for frequency control? Perhaps that’s wonky.
 
cafe latte said:
Wow what the previous owner doing!! C1 is supposed to be 0.22 UF 25v he has 0.47 100v
c4 not so bad 100uf 25v is substituted for the same with 100v
c5 is nuts 1uf 50v has been replaced with 10uf 160v!!!
c7 10uf 25v replaced with10uf 160v not ideal but ok I suppose
c12 100uf 25v replaced with same 100v, again ok
another curly one c19 1uf 50v replaced with 10uf 160v!!!
I dont think this is the issue but really not going to help!!
Need to see what caps I have, hopefully I can improve this.
Chris
Click to expand...
Besides the 200uF, is it obvious that the previous owner changed the values of the components? Sometimes the schematics do not get updated per changes the manufacturer has made.
I wouldn't worry about the 2 x 100uF, 175uF is/was still within spec (20% tolerance)
Also, the values of the rest not critical especially if not in the signal path.
Best
Soundork
P.S. This thread raised my levels of concern with regards part obsolescence, so in the middle of the night I pulled the schematic for my DP-1200. Luckily, I could still find NOS parts on that auction site for it. Phew...:)
 
Soundork said:
Besides the 200uF, is it obvious that the previous owner changed the values of the components? Sometimes the schematics do not get updated per changes the manufacturer has made.
I wouldn't worry about the 2 x 100uF, 175uF is/was still within spec (20% tolerance)
Also, the values of the rest not critical especially if not in the signal path.
Best
Soundork
P.S. This thread raised my levels of concern with regards part obsolescence, so in the middle of the night I pulled the schematic for my DP-1200. Luckily, I could still find NOS parts on that auction site for it. Phew...:)
Click to expand...
The previous owner is a retired tv repair man so my guess it he replaced the caps with the closest he had. It is possible that he did not have any 1uf so he put 10uf as it is closest he had. I know he has not been well and his work is clearly been done since he became unwell as really a mess and I know he used to be very good indeed.
Not sure what to check today? I will check resistors of course and continue to check around the pots and see that he has linked it all as it should be which from a quick check I think he has. Starting to run out of ideas..
Chris
 
Ordered a couple (spare one too) think that is next thing to try. If this chip was having issues and not totally failed maybe could cause drifting..
Chris
 
Bringing this thread back to life a 3rd time. I have a Denon DP-1200 I bought from Japan that arrived with the infamous platter spinning like a bat-out-of-hell issue. De-oxit on all pots and switches. No joy.

On the speed control board, all caps have been replaced. The semiconductor has been replaced, and the blackened leg IC semiconductor has been replaced. Still no joy.

The turntable progresses to a speed from start-up to the point where the plinth is shaking. I also readjusted and cleaned the magnetic speed control head as it had clearly been tampered with. Going to replace the blackened-legged TR1,2 and 3 C458 with the BC549.

Is there ANYTHING ELSE I should be looking at? Other than the blackened legs, the board and parts look like they came off the assembly line a month ago. None of the old caps looked like they had been compromised. The ONLY thing I see wrong is the blackened legs on the C458 and the IC. What am I missing?

The last picture is the speed control board when I opened it up for the first time. The red circled all the parts I replaced and the yellow is the C458 locations that are next on the replacement agenda.
 

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Squirrel! said:
Bringing this thread back to life a 3rd time. I have a Denon DP-1200 I bought from Japan that arrived with the infamous platter spinning like a bat-out-of-hell issue. De-oxit on all pots and switches. No joy.

On the speed control board, all caps have been replaced. The semiconductor has been replaced, and the blackened leg IC semiconductor has been replaced. Still no joy.

The turntable progresses to a speed from start-up to the point where the plinth is shaking. I also readjusted and cleaned the magnetic speed control head as it had clearly been tampered with. Going to replace the blackened-legged TR1,2 and 3 C458 with the BC549.

Is there ANYTHING ELSE I should be looking at? Other than the blackened legs, the board and parts look like they came off the assembly line a month ago. None of the old caps looked like they had been compromised. The ONLY thing I see wrong is the blackened legs on the C458 and the IC. What am I missing?

The last picture is the speed control board when I opened it up for the first time. The red circled all the parts I replaced and the yellow is the C458 locations that are next on the replacement agenda.
Click to expand...
If you believe you can repair this table by try and error method, it is wrong! Simply look at schematic and measure. You should not replace parts if you are not sure they are bad. Blackened legs are nothing important and do not point to possible fault. I had the same issue with Technics SP-15. Do not remember what was wrong, it was long time ago, but something very simple. So find technician.
 
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