Pioneer M-90 Issue- need help.

[Matt03221]

i would start with 100w or 120w (60+60 depending on availability) and see if the protection circuit has enough power to activate (latch the relay) and be stable. if not, then go up to 200w although constant high brightness is not a good sign. usually there is a bright moment when powering up from a cold start (power caps mostly discharged) after which the bulb starts to dim slowly.

using a kilowatt meter helps to see how hungry the system is, not easy to see otherwise. if the patient has a pulse and how high is the metaphorical heart rate, might be one way of looking at it.

Thanks again for you advice and wisdom! I was in Lowes yesterday and the lowest wattage incandescent bulb there was 200W- which I currently have. I'll keep looking. In the meantime, I just finished replacing the R-Ch 10, 100, 4.7. 47 and 6.8K ohm fusible resistors and zener didoes as well as tested all transistors and remaining didoes. Other than a few resistors a bit out of tolerance- nothing bad. Before I fire it up, I'm going to pull the chips, put in sockets, replace chips in the same spot and fire it up. If it acts the same and I can't nail anything down by checking voltages, I'm going to swap chips and see if the nonsense swaps with them. Been looking around for replacement chips just in case. A while back I bought a chip from "little diode" in the UK for my Technics SA-800 and it was legit and a reasonable price. They have P0016 chips available for like $80 a piece, so had to ask for more detail. Turns out they get those from a supplier in China who, they say, pulls them from used equipment. Just don't know if it's worth the risk even though they provided a legit ship before. A few options from China on ebay, but even with some sellers having good feedback- I just don't know, but the price is much better.

 

[sae-7125]

Lowes yesterday and the lowest wattage incandescent bulb there was 200W

part of the reason i use 40w+40w (candelabra base + standard base adapters) is finding a 2-pack at a dollar store, although now is 1.25 store since the price increase a few years ago. using 3 bulbs (40x3) would be easy for 120w.

worst case, can order filament bulbs online. i wonder what happens when using two 200w in series, if the cold filament resistance of one bulb helps to amplify the cold resistance of the other... might have to do some experiments on my bench, with the other oddities.

 

[Matt03221]

I think you previously mentioned doing some resistance comparison checks on the chips. What pin combinations would you recommend testing while I have them out?

 

[sae-7125]

lots of static checks for the chip, no idea if there will be a smoking gun as to leakage or something noticeably out of tolerance.


*a repeat from the previous page, to make things easier.

measuring across the current source pins (double circle symbols) would be a good starting point.

between pins:
1/14
7/8
9/13
8/9
13/14
10/11
11/12
1/7
8/14

comparing each chip upper vs lower outputs (each triangle symbol):
between pins:
9 and all its inputs
vs
13 and all its inputs

sometimes there will be an obvious low/high resistance but no guarantees there will be any useful data from this procedure. using an LCR meter at a particular frequency can find an anomaly when doing in-circuit diagnostics of circuit pathways but it helps to have "known good" range to compare the measurements with.

the joys of being a detective and flying blind for most of the case until things click, in a good way.

https://www.electronics-lab.com/article/current-sources/

https://www.reddit.com/r/AskElectronics/comments/awtvye/what_does_this_symbol_mean_on_this_schematic

*operational transconductance amplifier, pioneer chip might be a variation or something

 

[Matt03221]

lots of static checks for the chip, no idea if there will be a smoking gun as to leakage or something noticeably out of tolerance.

View attachment 3715319
*a repeat from the previous page, to make things easier.

measuring across the current source pins (double circle symbols) would be a good starting point.

between pins:
1/14
7/8
9/13
8/9
13/14
10/11
11/12
1/7
8/14

comparing each chip upper vs lower outputs (each triangle symbol):
between pins:
9 and all its inputs
vs
13 and all its inputs

sometimes there will be an obvious low/high resistance but no guarantees there will be any useful data from this procedure. using an LCR meter at a particular frequency can find an anomaly when doing in-circuit diagnostics of circuit pathways but it helps to have "known good" range to compare the measurements with.

the joys of being a detective and flying blind for most of the case until things click, in a good way.

https://www.electronics-lab.com/article/current-sources/

https://www.reddit.com/r/AskElectronics/comments/awtvye/what_does_this_symbol_mean_on_this_schematic

*operational transconductance amplifier, pioneer chip might be a variation or something

Still working as I get time. On the right channel I completed my check of all resistors and diodes I didn't replace- no issues noted. Moving on to the Left channel to do the same. In the meantime, I did resistance checks on the IC pin combinations you suggested with the chips off the board. I checked each combination twice- switching leads which is why you s 2 readings for each in my charts. All readings are in M-Ohms. Most readings are pretty close and might even be closer, but many of them fluctuate a bit. Only real difference between the 2 chips is the combination of pins 1/9 and 1/13. See anything in that?

 

[sae-7125]

Most readings are pretty close and might even be closer, but many of them fluctuate a bit.

LCR meter using various frequencies might shed more light in a specific direction but the dmm baseline should give a suitable picture. i wonder if diode check using the same pin configs, and probe swap, would reveal anything more??

looks like fluke 117 maxes out at 60meg (40meg range) so anything that hits overload/open is a significantly higher number vs the other meg-ohm readings.

Fluke 117 Multimeter For Electricians | Fluke

Check out the Fluke 117 digital multimeter for efficiency in low light. The ideal multimeter to prevent false readings caused by ghost voltage. Buy Now!

www.fluke.com

https://media.fluke.com/ce54d963-3be9-4e70-8a3e-b1060070fdfd_original%20file.pdf

youtube.com/watch?v=WTy-RM_1JLU
*resistance critique starts at 14:30

just a random dmm review search that had the data needed, various channels exist with delicious tech data to parse.


youtube.com/watch?v=PjNXbKlr3MI
*enjoyable/nerdgasm review/test/eventual break + autopsy + redesign + repair (part 2 vid carnage)

nerding out about diagnostic gear gets addictive and expensive, and now back to the original topic.

 

[sae-7125]

Only real difference between the 2 chips is the combination of pins 1/9 and 1/13. See anything in that?

indeed, looks like L-ch pins 1/9 there is a potential open. and r-ch pins 1/13 there might be leakage.

ultimately a new-old-stock known good chip will help compare in-vs-out of spec.

possible junction leakage on pins with measurable resistances (meg-ohm) regardless of probe polarity. L&R channels pins 4/9, 5/9, 7/9, 8/9 might be of some concern. either way the data collected is helpful and nicely formatted, gold star.

 

[hogdaddy]

Thanks again for you advice and wisdom! I was in Lowes yesterday and the lowest wattage incandescent bulb there was 200W- which I currently have. I'll keep looking. In the meantime, I just finished replacing the R-Ch 10, 100, 4.7. 47 and 6.8K ohm fusible resistors and zener didoes as well as tested all transistors and remaining didoes. Other than a few resistors a bit out of tolerance- nothing bad. Before I fire it up, I'm going to pull the chips, put in sockets, replace chips in the same spot and fire it up. If it acts the same and I can't nail anything down by checking voltages, I'm going to swap chips and see if the nonsense swaps with them. Been looking around for replacement chips just in case. A while back I bought a chip from "little diode" in the UK for my Technics SA-800 and it was legit and a reasonable price. They have P0016 chips available for like $80 a piece, so had to ask for more detail. Turns out they get those from a supplier in China who, they say, pulls them from used equipment. Just don't know if it's worth the risk even though they provided a legit ship before. A few options from China on ebay, but even with some sellers having good feedback- I just don't know, but the price is much better.

These signal lights should work just fine and they're heavy duty. I bought some.

Sylvania 12817 - 116A21/TS/8M 130V Traffic Signal Light Bulb - Incandescent Bulbs - Amazon.com

Sylvania 12817 - 116A21/TS/8M 130V Traffic Signal Light Bulb - Incandescent Bulbs - Amazon.com

www.amazon.com

 

[Matt03221]

indeed, looks like L-ch pins 1/9 there is a potential open. and r-ch pins 1/13 there might be leakage.

ultimately a new-old-stock known good chip will help compare in-vs-out of spec.

possible junction leakage on pins with measurable resistances (meg-ohm) regardless of probe polarity. L&R channels pins 4/9, 5/9, 7/9, 8/9 might be of some concern. either way the data collected is helpful and nicely formatted, gold star.

I have 2 pairs on order- 1 from a place in Canada and another in the UK. They say they're legit, but I guess we'll see.

 

[hogdaddy]

I own a stock M-90 amp also it's a is a great amp.

 

[Matt03221]

Still checking components and while doing so noticed R246 in the protection circuit is not there. Circled in red on the attached. My guess is it's not supposed to be there but noticed two other posts on AK mentioning the same missing resistor, but no conclusions on whether it should or shouldn't be there. In one post, guswin95 said he's seen some units with and some not. Protection circuit has not yet been my issue but would be nice to have some clarity if there is any.

 

[Matt03221]

Finished my R-Ch replacement and/or check of resistors, transistors and diodes and found nothing notable. Thinks what I'm going to do is wait for my ICs to come in and see how the compare to the originals before I do anything else- even thought it a take a bit before they show up.

 

[sae-7125]

updates about the project are always good, regardless if major or minor. sooner or later a conclusion will be achieved and thats when all the puzzle pieces make sense... and music.

 

[Matt03221]

Thanks for the follow up. Still waiting on the chips. Shipped but no tracking. If i get bored waiting I may put the originals back in but flip channels to see if the symptoms move with the chips, but a little hesitant. Don't want to screw anything else up.

 

[Matt03221]

Wow, both sets came in the same day. One from Ireland and one from Canada. Think there's any risk of damage if i run another resistance check like i did with the originals? Wasn't too worried about them as i assumed they were bad, but these i don't want to risk if there is a risk.

 

[sae-7125]

Think there's any risk of damage if i run another resistance check like i did with the originals?

shouldnt be an issue, only concern would be esd when handling the chips. easy enough to touch earth ground or wear an esd wrist strap.

the numbers comparison would be interesting to see, amp chips vs new old stock. using dim bulb around 100w after the new chips are installed would be a safe start and then measure dc bias to verify nothing is unusually high or unbalanced between channels.

 

[Matt03221]

shouldnt be an issue, only concern would be esd when handling the chips. easy enough to touch earth ground or wear an esd wrist strap.

the numbers comparison would be interesting to see, amp chips vs new old stock. using dim bulb around 100w after the new chips are installed would be a safe start and then measure dc bias to verify nothing is unusually high or unbalanced between channels.

Chips from Canada (Vintage Audio) don't look like the originals and most of the pin combinations read open. The chips from Ireland (Donburg) look legit compared to the originals and I've included the readings here. Each pin combination was checked twice switching the meter leads each time (hence the teo figures) although I didn't track which reading goes with which lead orientation. "0" means open, not o-ohms. Readings are notably different from the originals above, but also different between the two and I've highlighted the most significant. Previous readings from the original chips are included below the new chip readings. I've not yet tried the new chips in the amp. Any concerns doing that?

 

[sae-7125]

lots of delicious data points to consume, this might take a few moments. should probably find a bib, bits and bytes all over the clean desktop wallpaper...

 

[sae-7125]

page-1 numbers seem to line up with one possible exception (5 to 9). since everything is in the meg-ohm range things should be fine. the only uncertainty is when the chips are in circuit with power applied.

start low and go slow with a variac would be my initial startup procedure, dim bulb safety net active as well. monitoring channel dc bias at all times. if the bias goes into runaway or is out of spec even at low voltage startup, having a amp/current limiter is important. the protection circuit might get unhappy about being choked/limited but its no big deal.

 

[Matt03221]

page-1 numbers seem to line up with one possible exception (5 to 9). since everything is in the meg-ohm range things should be fine. the only uncertainty is when the chips are in circuit with power applied.

start low and go slow with a variac would be my initial startup procedure, dim bulb safety net active as well. monitoring channel dc bias at all times. if the bias goes into runaway or is out of spec even at low voltage startup, having a amp/current limiter is important. the protection circuit might get unhappy about being choked/limited but its no big deal.

Thanks for looking that over. No variac on hand. I have the option of 1 to 4, 40W bulbs on my multi bulb mount for the DB tester. Since the right channel wasn't too bad i may stick the original chip back and go with chip 1 on the left and see what happens.