EV 3000 amp fault...

[plec.22]

Has anyone had this odd fault? EV P 3000..

Here goes..after repairing both power stages within this unit, itwas time to power up..
click went the relay's all good there next was the task of setting the bias/ht and offset to both channel's as out lined in the files...

Here's where things start to act odd...A chan..set's up all good but, B side offset is high 300mv! it should be 10mv...I rechecked each connection even changed over the power block's in order to ensure the front end pcb's are ok and all it well there...

1)checked all plug connections
2)checked all voltages as out lined
3) rechecked each part fitted from resistors,transistor's etc...
4)metered each track to each component yawn yawn...

next re powered it back up and it's still the same 300mv to 10mv...and you cant even adjust the offset trimmer to bring down the high offset volt.

The dc trip will act if there's a volt on the o/p but it's not acting due to it's offset volt.

Why is there is 300mv's on B side?? even when cold check's are the same...

it's a case of looking at things to long trying to see the answer...

Has some had this same fault before?

[Jazz P Bass]

Can you post the schematic?
My first thought is the long tailed pair input.
If you caught everything.
Barring a dc offset pot, that is a good place to start.
If you have replacements, yank em & install two new ones.

[doctor]

I have the P-3000 owner’s manual, which de facto is service manual including schematics.

The document’s size is 4.5MB that exceeds forum’s limit for PDF file.
I could split this file in two RAR files, but forum’s file upload manager does not allow to upload files of such format.

Finally, if anyone needs aforementioned information, send me your e-mail.

Can you post the schematic?
My first thought is the long tailed pair input.
If you caught everything.
Barring a dc offset pot, that is a good place to start.
If you have replacements, yank em & install two new ones.

[plec.22]

Thanks for reply Jazz p Bass,

I've started reworking it again and fitted new mj350's/340's.. as Doctor say's he can mail over the info cos the file is to big for posting on here..

The main power/protection/driver circuits are working fine as I've swap round the power amp block's and the dc offset pot work's on the good channel it's only the left channel that has the high 300mv setting on it's out put. I did think it was the bypass caps linked across Q40/Q39/Q19/Q10..these are 680p. even the bias transistors have been changed out.

thanks again for your reply.

[plec.22]

Hi Doctor.. Have you had this odd fault after servicing this amplifier? it's a pain in the butt having to keep fitting the board's in and out just to power it up.

it's an odd one as once things have been fitted the right way in and cold check's have been done and both sides read the some it act's up!

[plec.22]

I even started thinking could it be the board itself? as in the passed I've seen folk say after fitted fresh parts it worked...

I would like to get the odd dc offset to the same setting as it's working channel..10mv

[Jazz P Bass]

I have the P-3000 owner’s manual, which de facto is service manual including schematics.

The document’s size is 4.5MB that exceeds forum’s limit for PDF file.
I could split this file in two RAR files, but forum’s file upload manager does not allow to upload files of such format.

Finally, if anyone needs aforementioned information, send me your e-mail.

The best way that I have found to knock down a file.
Link: CutePDF - Create PDF for free, Free PDF Utilities, Edit PDF easily;.
It sets up as a printer. Then you can print page 1- 8 & page 9-12 (or whatever)
The best thing (besides being freeware) is it prints to a pdf file.
Simple, huh?

[J M Fahey]

Agree with jazzpbass suspicion on the long tail (or differential) input pair.
MJE's are'nt really great for that job because they are optimized for a relatively high power (plus standing very high voltage) so they do not shine there, specially because of low beta and possible parameters spread.
300 mV sounds too much as unmatched parts offset (it should be around 50V, 100mV tops) *but* if the actual input one has very low beta, its biasing base current, flowing through the resistor to ground, may explain those 300mV.
Measure voltage across said resistor (often 10K value) and base to ground voltage for both transistors.
I think you may find some discrepancies there.
Good luck.

[plec.22]

J M fashey, thanks for your input on this on going fault.... the design for this amplifier uses mj340/mj350 and mpsa42/92 for the long tail input stage plus all replacement part's are as stated from the file spares list. dc offset adjustment says 10mv +/-. it's bias setting it spot on at each setting in this amplifier there is a cold bias and hot setting and this are set to 15mv all is fine there.. the file can be found on line and down loaded for free..

in my early comments each part on the pcb has been check each resistor and so on..even cold check's from ground to each side A or B all reading are the same!

yet on powering it, it does it's safe check's then the relay's click over on the speaker o/p end... here's some of the transistors...Q51/Q52/Q53/Q54 =MJ350 AND Q61/Q58/Q60/Q59 are mj340.. then driver's are 2sc3281/2sa1302... o/p are mj15022 and mj15023's all test fine on leakage...here's the thing I even swapped o/p devices to the working channel all was fine there for channel (10mv) but channel 2 was still at 300mv?

I've even lifted each resistor to ensure there reading the same valve, these are 1% metal types high voltage...

I n the file 50mv on the out put would be to high aswel... and after rechec the working side the reading is 10mv spot on..it's an odd one here me thinks!!

[J M Fahey]

Fine, but *did* you check

Measure voltage across said resistor (often 10K value) and base to ground voltage for both transistors.

Also please post the direct link to the amp schematic so we all have the same version.

[plec.22]

following the ref points out lined on the schematic..float v is 67+/- Q47 ref point is -11v and zener diode ref 7v5 is correct.. the file is to big to post on here as Jazz p bass was looking for it..I could sent it to your email as the p2000 is the same as the 3000 stage..

[plec.22]

here's were the schematic can be found retrevo.com this page link has the ev 3000 file..

[plec.22]

Ev p3000 power amp file found @retrevo.com..

[Jazz P Bass]

EV P3000 Owners Manual w/ Service Info
[urlhttp://www.step.polymtl.ca/~polyshow/doc/manuels/P_3000_Owners_Manual.pdf[/url]

[plec.22]

Thanks posting link Jazz p Bass.

the o/p stage take's a little time to look over and you'll see how the bias hot and cold settings are...