DB technologies hpa 1400 or RCF hps 1500 schematics needed

[NO-ALI]

hi everyone , its my first thread on this website , i just bought 2 rcf hps 1500 power amps , they are both faulty , i started working on them but i really need the service manual or schematics for it , i'll be really thankful if anyone can help me with that , thanks .

[NO-ALI]

hi everyone , its my first thread on this website , i just bought 2 rcf hps 1500 power amps , they are both faulty , i started working on them but i really need the service manual or schematics for it , i'll be really thankful if anyone can help me with that , thanks .

up up up

[The Dude]

Have you tried contacting them directly?

Contacts - dBTechnologies

RCF - Sales Support

[NO-ALI]

thanks for the replay , i did , all they keep saying is that i must take the amps to the closest RCF dealer , we dont have one in Tunisia

[mozwell]

try Download hps1500 Manual or hps1500
i think you may have to pay $4 or so

If you are not comfortable working inside an amplifier with DC voltages up to +/- 100V, and don't know how to do this safely, then i would take these amps to someone who knows what they are doing. We don't want you killed.
How experienced are you with electronics ?

from what i can see on the preview, it looks like parallel hi side & low side power transistors, without dual pos / neg rails & switching between rails, so we should be able to work on this without a schematic, at least to do some basic faultfinding.

They look to have an op amp input, so lets start with:
1. What is the problem (try and add as much detail as you can)
2. With power off and disconnected from the mains, measure between the two supply pins of your mains plug (ohms)
3. Are there any fuses, also there may be fuses inside, are any of these blown
4. With power OFF, measure OHMS between the 3 pins of one of the power NPN and one of the power PNP transistors.
5. With power on, can you measure from between pin 4 and pin 8 on any 8 pin op amp, DC Volts
6. With power on, can you measure from 0V (speaker negative) to each pin of the NPN and PNP power transistors DC Volts

[NO-ALI]

thanks for the link i looked everywhere for it , i have some experience with repairing electronic things , but i'm new in power amps repair , in the first amp , 1 channel is working fine , the other one works too but as soon as i turn the volume knob up , the limit light is on and i can only get a distorted sound from the output , and if i turn it up more it will go on protect mode , i tested all the power transistors and they are all fine , i took some measurements to compare the 2 channels , both channels are getting a -45 v and +45v , on the working channel when i feed some signal to the amp and mesure the voltage on the base pin , its just some mv , but on the faulty one its at about 2 to 4 volts when there is no signal coming in , when i put some signal on and turn the volume up it goes to about 17v then it goes to protect mode , i took measurements on the op amps and they all have the 14v they need to operate , the other amp is always in protect mode , but when i disconnect the channel 2 positive supply cable the protection relay clics and only one channel works , and the limit led is on for the faulty channel , tasted all the transistors and they are all fine , even tried and took off all the power transistors from the faulty channel and its still not working when the positive power supply for that channel is connected to the main board , and there is about 6v on the base of all transistors on that channel , thank you all for your help

[mozwell]

Hi Ali
Its good you have one working channel & one bad one, that makes it easy to compare. If you can get the schematic from the download link that will help a lot.
For now, we don't need to put a signal in, and when we measure volts, please note if they are AC or DC, it does make a difference

We have +/-45V going to each power amp, and +/-14V going to any op amps.
1. What is the part number of the op amps TL072, 4558, 5332 (etc)
2. If they are dual op amps, check we have -14VDC on pin 4 & +14VDC on pin 8
3. If they are dual op amps, check the AC and DC voltage on pin 1 and pin 7 of each op amp
4. Please check using AC and DC ranges on your multimeter the +14V, -14V, +45V and -45V supplies. DC measurement will check the voltage level, AC measurement will check the ripple on the supplies
5. Please check using AC and DC ranges on your multimeter the speaker output positive terminal on each amp.
6. Please check using the DC range on your multimeter, the bases of each output transistor, on both channels

With power off and all power supplies discharged, please measure for each channel
7. resistance of any power resistor in series with each output transistor (normally a 5W white ceramic resistor, 0.22 to 0.47 ohms)
8. resistance of each power transistor, collector to emitter
9. There shoudl be a driver transistor for each group of output transistors, please measure resistance of each driver transistor, collector to emitter

That should do for now & will determine what we check next.

[NO-ALI]

hi Mozwell , i got the schematics , http://https://www.dropbox.com/s/3ob7gmyo867ko6p/HPS1500.pdf?dl=0 ,
all the op amps are MC33078 there is no tl074 like in the schematics , they all have the +and -14v DC , When i do the measurements on AC i got 0 instead of -14v and 30 instead of +14 , 0 in -45 and 90v in +45 , the speaker output positive terminal has about -4.5mv on the good channel and -3.8mv on the faulty one , and after about 15 sec of turning the amp off it goes to about 60v
all the power resistors are fine 0.47 omhs on each one ,
on the positive side of the power transistors i got about 460 ohms from collector to emitter , on the negative side i got about 480 ohms
and there is something else that i dont really understand , when i feed a 1khz signal the faulty channel start clipping even on low volume then it goes on security mode when i turn the volume up , but with a 20hz signal nothing happen and both channels works fine

thank you so much for your help

[mozwell]

Hi Ali
Thanks for the schematic, it is confusing & may have errors (eg +15NTC is shown in two places, coming off 2 different zener diodes)
This thing has rail switching, so its a lot more complex.
We don't need to test with a signal, or a load at the moment
Lots of supply rails & lots of things to check
There looks to be a bridge / stereo switch, put this in stereo mode

Lets start again, from the start.
For ALL the measurements below, use both AC and DC ranges
Please post the results, for example, mid rail + is +45VDC and 0.1VAC, or D28 cathode +10VDC and 0.01VAC
Always put + or - on DC measurements when you write them down
Put the black multimeter probe to 0V, we will leave the black probe here for all measurements, a good place is the metal tab of 7815 IC1

Various internal power supplies
1. +mid rail, cathode D38 or D19 or D44
2. +hi rail, whichever end of R94 reads more positive or Q13 Drain
3. pos ref, whichever end of R92 reads more positive
4. +15NTC, cathode of D39, also cathode of D53
5. -mid rail, anode of D41 or D20 or D45
6. -hi rail, anode of D42 or Q16 Source
7. neg ref, whichever end of R97 reads less negative
8. -15NTC, anode of D40, also anode of D54
9. +15V, anode of D4
10. -15V, cathode of D11
11. +13VCL, whichever end of R246 reads less positive
12. -13VCL, whichever end of R247 reads less negative
13. +14VIC, pin 8 of U1
12. -14VIC, pin 4 of U1

And for some opamp / comparator power supply levels
13. pin 8 of U2
14. pin 4 of U2
15. pin 8 of U3
16. pin 4 of U3
17. pin 8 of U4
18. pin 4 of U4
19. pin 8 of U5
20. pin 4 of U5
21. pin 11 of U6 or U7 TL074
22. pin 4 of U6 or U7 TL074
23. pin 8 of IC3 LM393
24. cathode of D3
25. cathode of D28

Power amp output
26. Anode of D19
27. Anode of D44

Now we need to measure some comparators, black lead does not connect to the tab of 7815 IC1
28. red lead to pin 8 U4, black lead to U4 pin 4
29. red lead to pin 8 U5, black lead to U5 pin 4
30. red lead to pin 8 U7, black lead to U7 pin 4
31. red lead to pin 8 U8, black lead to U8 pin 4

Turn power off, wait until all the power supplies are discharged, we need to measure some transistors & diodes
32. ohms C to E of all power transistors (we just want to see if one is shorted)
33. ohms D to S of mosfet Q13, Q16, Q19, Q22 (we just want to see if one is shorted)
34. use the diode range & check with both polarities of multimeter leads, D28, D30, D34, D37

This should tell us where to start looking next

[NO-ALI]

hi Mozwell

i just found the fault on the amp and its working now , i think it was just luck i did some testing to smd transistors and diode and i found that Q18 and Q20 are shorted , and D10 has a resistance both ways , i changed them and its working just fine , i tasted the same components on the other amp and it was the same fault , exept that Q59 and Q69 where shorted too , i have few questions , is it a bad design problem , since both amps have the same problem ? do we need to do the other measurements that you told me about ? and in case everything is fine , how can i do the biasing for this amp , and without knowing the right values for it , is it still possible to do ?

thank you so much for your help

[mozwell]

Hi Ali
Glad you found the problem

As Enzo often says, don't find a reason NOT to test something....

I would not think these failures were a design fault, but we can do some quick checks to verify these transistors are ok to use in these positions

Since you found some transistors & diodes that are faulty, a quick check of all the transistors & diodes (with power off) would be prudent to do, especially as it doesn't take too long.
Its still worth double checking the power supplies, just in case one is not what it should be. While you have the amp open, its quick to do.
Check each supply using the VDC and VAC ranges on your multimeter. On all power supplies you should have "normal" VDC for each voltage supply & small VAC (low ripple on the DC supply)

The other thing to check is bias current for the power transistors
Measure the voltage across each of the 0.47 ohm 5W resistors, they should all read a low mVDC reading and all readings should be very similar.
None should read 0mVDC
The bias current for each transistor is then the mVDC reading / 0.47 ohm
Leave the amp on for 10 minutes or so & check the mVDC reading across each of these 5W resistors again.
Make sure the heatsink doesn't get warm (it may get a little warm, but not too much)
Generally 20 to 50mA is ok for bias current, so if the mV reading is between 10mVDC and 22mVDC you should be good to go

Lets check voltage across the transistors you found were faulty
We only need to check one amplifier for this
Measure VDC across Q14 C-E. I would expect this to be less than 10V. If you measure less than 10V then there is no design flaw. If you measure more than 20V, then check all the resistors around this area on all the amplifiers to make sure no resistor has gone open circuit, do this also for the area around Q15, Q59, Q60

The other thing i would check is the low rail / high rail switching is working ok
You already measured the low rail as +/-45VDC
Turn the volume control to minimum and inject a 400Hz or 1kHz signal to the input and monitor the output voltage, no speaker connected.

Slowly raise the volume control & watch the output AC volts. You should be able to get much more than 28VACrms on the output.
If the hi rail volts is 90V you should be able to around 60VAC on the output.
If you can get this for both channels, then the rail switching is working ok & you are good to go.

If you have a dummy load, you can run the unit at (say) 75% output power & leave it running for several hours. If the unit works ok, then you have two good power amps to enjoy

Glad you fixed it