Any Phase Linear Experts out there?

[releone71]

Many thanks for keeping in mind the P/L parts I was looking for. Unfortunately the faceplate from model 400 series II won't fit :-(...

Glad you have acquired the new 700B Toy. I bet you are already planning some restoration works. Have a great time then! I am traveling for two more weeks, so rarely coming back to the posts...

Hi P.L.F., you're the welcome!!.
Regarding the 700B, every part in the amp is 100% original, except the power cord. I cleaned the inside from dust and the pots with deoxit but I can still smell that bad smell. I can see also a thin grey film over the PCB and the white Sangamo caps, not so sticky though. I'm now aware that bad smell is not from the smokey environment of a disco, it's like the amp was rather used near the domestic fireplace. It's the typical smell of burnt wood. I've played several CDs yesterday from afternoon till evening and the amp worked perfectly.
I checked the offset across each output terminal and I read a tension of 10.5mV which gradually raises after half an hour to 15.5mV in the left channel and 0.5mV(?!) in the right channel. According to the 700 II manual, the correct value is 10.0mV, but is it valid for the 700B too? Even if I can say the amp stayed relatively cold while playing music yesterday afternoon (about 3 hours), do I have to change the offset setting? Or I'll better let things as they are untill they work? Could it be the difference in the readings between the channels an issue due to the old trimmers on the PCB? In any case the service manual and any other useful advice would be appreciated. Thanks!!

 

[d3imlay]

I checked the offset across each output terminal and I read a tension of 10.5mV which gradually raises after half an hour to 15.5mV in the left channel and 0.5mV(?!) in the right channel.

The 700B has no adjustment for Dc offset. The only recourse is to match Q1/
Q2.

 

[Sound Dragon]

PM replied to

 

[releone71]

The 700B has no adjustment for Dc offset. The only recourse is to match Q1/Q2.

Thank you so much, clear now. I forgot the trimmers on the PCB are for the bias setting, right? Do you think it's time to replace those transistors or any other component which could have drifted?
Wanting to measure the bias value, where do I have to perform the reading? Across any of the output resistors (R38/R39 for example)? Which DC value? Thanks.

 

[laatsch55]

Yep, Negative meter probe on the output terminal side of R38. R 20 is your adjustment point. you are looking for 350MV DC , +/- 100mv.

 

[P.L.F.]

Just got quite rusted P/L 700 series II 'patient' on my test bench, with fully comp. output. I think someone must have kept it outside looking at the corrosion present. No doubt metal surface cleaning / varnishing will be needed. Anyway, slowly - since I am busy with other activities - this new project will be pursued.

Veeery slowly progressing with the project... Disassembly, taking out corrosion from chassis parts, black varnish - all done. The PS caps replacements' reforming also finished.

I am in the process of a complete restoration of the PL36 PCB as I think the amp took too much humidity (rain?) and some components / wiring seem to be visibly degraded. Fortunately the transformer works OK. Need some advice and experience to be shared on the following:

(i) purpose of a cable that I found not ended/connected: below is the photo attached, where PS caps are removed;

(ii) the best location / way of mounting of speakers protection circuits for the 700 II model: I have 2 spare units to be deployed (picture enclosed), but in this model there is not that much space to use - any recommendation?

(iii) PL36 connections marking for fully complementary stage: I see color marking discrepancies between the manual/service bulletin versus reality (see the pdf). Can trace each cable of course if no advice found. However if anyone from the P/L enthusiasts made an exercise to put the right connection number from the PL36 schematics next to the color listings for both amp. versions quasi- and fully-complementary, that would be great to share. It may looks as follows: wiring sequence numbering on PL-36 PCB COMP starting from the 'RIGHT INPUT HOT' and ending up with the 'B -' wire - to keep the same order as in the service manual:
(1) right input hot - RED,
(2) right input GND - GREY,
[...]
(27) B- DC supply - BLACK
and the same for QUASI topology for future repairs.

Thanks for any valuable support to 'decode' the marking of [...] and advice regarding earlier points too!

 

[laatsch55]

PLF, have you put a mter on the terminated wire by the p s caps to check voltage? That might give us a clue. On the point to point wiring off the board, if its been worked on before I would trace each wire per the schematic.
The attached file is the PL 36 board connection I have, might help.

Also per service bulletin of retrofitting a PL 36 drive board to a series I output stage the board wiring is the same as the the PL 20 board, so if you have a board wiring layout for the PL 20 board that would work too.

 

[P.L.F.]

PL36 PCB wiring & marking

PLF, have you put a mter on the terminated wire by the p s caps to check voltage? That might give us a clue. On the point to point wiring off the board, if its been worked on before I would trace each wire per the schematic.

Hi Laatsch55,
I haven't examined the voltage of the suspicious cable yet, will do it if after measuring resistances still no new idea flashes out. To measure voltage I'd need to disconnect completely the transformer secondary - foreseen next step.

In the meantime I did some 'homework' and added interconnections numbers marking for the driving board (PL36) quasi-complementary output. Might help in other P/L restoration projects - see the attached info.

For the one laying on my test bench - need to trace cables indeed. You're right, someone worked on it trying to bring the beast back alive... Work in progress...

 

[laatsch55]

Prior work on a unit means some close inspection and don't ASSUME anything, good luck Bud.

 

[P.L.F.]

PL36 wiring & marking - fully comp. output stage

Prior work on a unit means some close inspection and don't ASSUME anything, good luck Bud.

I think, cracked it... It is apparently undocumented PCB version of PL36 designed for fully complementary output - have a look at the pictures attached (specially #3). There are two key points that seem to be different:
- factory embedded solution to cure possible oscillations at NPN/PNP predriver stage (cer.cap C->B)
- new wire: pre-driver C -> output common C.
Worth to mark it on the schematic - I leave it for a volunteer ..
Inspection will be continued...
Cheers

 

[laatsch55]

The ceramic cap you pointed out was was the factory solution for the oscillations, you are correct. They called it a slowdown cap.

 

[P.L.F.]

Phase Linear 700 II rewiring - cont.

Following my post #124, here are some principles discussed here and on DIY Audio that I'm going to follow for the gear currently under a complete restoration (previous posts exchange):

ISSUE:
- RCA input ground tied to the input ground of the amp input circuits (not a star topology).
SOLUTION:
- Leave it as is.

ISSUE:
- Speaker terminals ground tied to the RCA and driver board input ground.
SOLUTION:
- Cut the grounding connection of speaker terminals, draw instead a new grounding wire to the PS caps common point clad.
- Move the driver board ground to the power supply ground, at the junction of the two PS caps.

ISSUE:
- 230VAC, B+/- DC and low level audio wiring run in a bundle all together
SOLUTION:
- Unbundle all the leads carrying AC, DC and audio.
- Shorten the DC power leads by directly routing them to the capacitors from the output stage.
- Shorten the ground leads in the same manner.
- Reroute the audio wiring from the rear apron directly to the front panel.

ISSUE:
- Hum or crosstalk, if still present
SOLUTION:
- Consider partial shielding of the driver PCB with a strip of copper clad on the left edge, right over the 5" trace of unshielded audio input, grounding that strip to audio ground.

I welcome any correction or further advice!

 

[laatsch55]

P.L.F. sounds like you have it under control.

 

[P.L.F.]

Phase Linear 700 II restoration progress and problems found

Hello,
.. a long silence on this thread...
My renovation works continue. Here is what was done so far (not in order), some pictures will follow soon:

• Complete rewiring: separating/rebinding AC, DC, audio signal (and adding shielding between RCA inputs and PL-36 PCB);
• RCA input posts replaced with gold plated version
• Speaker posts replaced heavy duty gold plated type
• Volume pots replaced with BLUE ALPS RK27
• All emitter resistors replaced with 3W 5% matched new ones (among old resistors three were found completely drifted)
• Input coupling caps (.47uF) replaced with HQ V-Caps
• Four electrolytic caps on PL-36 replaced with new Nichicon high grade
• AC cord replaced
• PS electrolytic caps replaced (new reformatted before mounting)
• Speaker DC protection/delay PCBs installed and wired (to be activated at the very end restoration process)
• 7,5K 5W and 7,5K 3W resistors replaced with matched ones (old had too significant resistance difference)
• TL071 op-amp is replaced with BB equivalent OPA134
• All outputs taken out, radiators cleaned from tons of thermal compound (several xstrs had only the compound between mica and radiators)

At the beginning I tested all PL-36 transistors and diodes in circuit in line with the service manual – no problems.

However here is my issue: before taking out the power transistors and drivers I tried to check/isolate potentially shorted outputs. On one bank, upper pole channel right, PNP MJ15025 xtrs type, between collector buss wire and every emitter the ohmmeter reading was 2-3 ohms only (step 6-1.3 in the manual). After all outputs and applicable driver were out I did the test again – same result. I rechecked all transistors and diodes on PL-36 and again nothing suspicious found. Theoretically the problem could be caused by shorted D107, but not sure where it is – have a poor copy of the parts location schematic, still all diodes on PL-36 are OK. But maybe there is something else. I need to solve this problem before bringing the amp up and its fine-tuning/testing phase.

Please advise!

 

[laatsch55]

Have you checked the 1n4004 diodes on the terminal posts by the output sockets? also check each socket for isolation. check zoebel network on speaker posts.Then check vu meter harness,

Just remembered, you are working on a series II aren't you?

 

[P.L.F.]

Have you checked the 1n4004 diodes on the terminal posts by the output sockets? also check each socket for isolation. check zoebel network on speaker posts.Then check vu meter harness,

Just remembered, you are working on a series II aren't you?

Hi Laatsch55,
Yes, it is 700 series II with fully complementary output stage. OK, I will check 1N4004 - is one of them D107? Zobel filter? Good point, I saw one cap replecement by somebody - will check again...
Thank you.

 

[P.L.F.]

OK, here is the recheck status:

• Cannot find any diodes at terminal posts - are you sure they should be there?
• Zobel filter is OK
• Hate to even think about the socket isolation - disassembling will be veeeery time consuming, I leave this option at the very end of problem solving...

Just to repeat the issue: I have no proper resistance reading between upper pole common collector buss and any of the emitter contact on the TO-3 socket, unlike it is for the lower pole (ca. 700+ ohms) and the whole left channel similar measurements (see comp version full schematic in attachments).

Any other thoughts?

 

[laatsch55]

D107, 108 are suspect, also D102 and 103. 107, 108 shpould be between the collector bus bar and the stand alone terminal down with the sockets. Have you checked isolation on the sockets to ground?
C110, C111 check good too?

All emitter resistors good?

 

[P.L.F.]

D107, 108 are suspect, also D102 and 103. 107, 108 shpould be between the collector bus bar and the stand alone terminal down with the sockets. Have you checked isolation on the sockets to ground?
C110, C111 check good too?

All emitter resistors good?

A mystery... No D107 & D108 there and D207 & D208 on the other channel ... Can they be on PL36 board? Still measuring 'in circuit' I checked all diodes on PL36 and no shorted one found. C110-111 give 'shorted sound' on DVM (diode/ohms meter on) until these caps are fully charged, then it's OK. Isolation of sockets to ground OK. Emitter resistors (.033 ohms) would not cause the problem, I guess. Anyway before putting them in, all were carefully measured and matched.

More advice needed pls

 

[P.L.F.]

Just one more info.
Apparently some last models of 400II and 700II comp. output had no flyback diodes, that we were looking for, at all... More info here: http://www.diyaudio.com/forums/solid-state/169883-phase-linear-700-series-ii-restoration.html.
More problem pursuing required...