Pearl 3 No Gain

[runclesid]

the bottom 2 test points, 19v & -19V, are those a source, 19v and drain

Those are the supply voltages for the board. Source 'S' and drain 'D' are on the jfet devices, Q1, Q2, Q3 and Q4. They are the 2SK209 (this schematic 2SK170) soldered to the board not far from the MM/MC gain jumper by the DIP switch. Those were the voltages I was noting.

 

[Toys4Boys]

I've metered the left channel less a few test points on the bottom of the board. Most are very close to what was referenced, the obvious problem is Q8->R21 which shows no voltage.

Uneducated guess, Q8 needs replacing.

 

[6L6]

Yes, that’s a logical place to start.

 

[Toys4Boys]

Does that compute based on feeding the cartridge to the out?

 

[6L6]

I mean maybe perhaps?

Failure modes are very difficult to predict. Something went wrong, circuit reacted unfavorably, now it’s time to determine what went boom and fix it.

All part of the fun.

 

[Zen Mod]

nothing to do with cartridge at out, but with what you put in input

 

[Zen Mod]

I mean maybe perhaps?

and I mean wtf maybe perhaps whocares

 

[6L6]

Exactly.

 

[Toys4Boys]

Well, I guess I do a bit, besides I don't have anything better to obsess on till I get replacement . That would be the Iron Pre input into the Pearl input.

To be clear, the schematic, post 10, references ZTX851, the Build Guide shows various alternatives. Suggestions are welcome.

 

[Zen Mod]

you don't need any other explanation than - static or Gremlins

whatever else you can think of, is not going to give certain explanation

neither thinking of impedances nor thinking about voltage

believe me, after decades in Service side of things, I did learn not to obsess about nonexplainable , instead taking care of my own standards in repair

 

[6L6]

Yes, replace the 851. Digikey has almost 9000 in stock.

https://www.digikey.com/short/5j0thv41

 

[Toys4Boys]

^ Yeah... I meant, is there an advantage or sonic difference between the options?

 

[6L6]

The circuit was designed for the ZTX851. Any substitutions offered were in lieu of having 851s, (because they were very hard to get for a while durning the lean semiconductor years post covid) and the substitutions given would have no detriment to the circuit. Of course there are a number of transistors that will wok great, but as a quick look on octopart shows a couple hundred thousand available through various distribution channels, get 851s.

 

[Toys4Boys]

Parts have shipped! Most anxious to get it back in the system, the last few days I have given the JC Jr. a good workout and want to compare.

 

[BDP]

I've metered the left channel less a few test points on the bottom of the board. Most are very close to what was referenced, the obvious problem is Q8->R21 which shows no voltage.

Uneducated guess, Q8 needs replacing.

What is the voltage on the other side of R21? You should see most of the 15 volt supply from the voltage dividing network R19 and R20

 

[Toys4Boys]

^ That'slogical , I'll check that tomorrow. Thanks!

 

[Toys4Boys]

Looks like I'm going to have some spare parts! Went to dbl chk what @BDP suggested and went back thru my TP's, lo and behold the offending point now measures correctly. What's better is that it's back in the system and sounds great! I would have thought perhaps a cap needed to discharge, but it was disconnected fro power for several hours previously.

 

[runclesid]

Glad it's working again Toys4boys! It is strange, I had a similar event happen when doing the initial build testing. I had touched a couple ZTX851 transistor leads together with my probe while measuring the voltages. It took out that board for a while. I left it powered off then it was eventually working again later that day. It hasn't clamped or failed since I leave it alone with the cover on. Hope that is all is for you.