Differences

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--- hotrod [2023/02/15 10:22] – wadmin
+++ hotrod [2023/02/15 15:59] – [Bugfix #5 - Glue them all] wadmin
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 {{drawio>hotrod:sp1test.png}}
+----
+===== Bugfix #0 : Cleaning =====
 ----
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 Then, failed tubes can cause rattle so we need to check them. This is generally linked to some inner part mechnically broken, but still electronically connected leading to vibration-induced noise. Power-on the amp and take any kind of chopstick. Put the amp volume to 2 and softly - extremely softly - tap the preamp and power tubes. You should not hear anything on the speaker. If you hear some sort of dull tick with a damped ringy reverb, then you might have some failed tube ringing issues. Change the ringing ones with a replacement one.
 ==== Dampening preamp tubes - easy rubber mod ====
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+===== Bugfix #3 - Refresh soldering =====
-If your tubes are good, but rattling still persists, it's time to check the guts of the amp.
+HotRod's PCB quality is highly questionable, leading to several component/soldering issue. This section tackles mspecifically soldering and PCB problems.
+==== Rework solder joints ====
-===== Checking the electronics =====
+Inspect PCB and look for suspicious solder joints as per those detailed here https://meyerems.com/effective-soldering-iron-rework/
-''Disclaimer (again...):
+You want to investigate in priority the following components:
-- first and foremost, just consider taking your Hotrod to an Amp shop. All the suggestions in this section are targeting those who have basic knowhow of electronics, soldering and high voltage designs. Opening your amp exposes you to high voltage which is extremely dangerous. Do it at your own risks.
+=== Critical heating components ===
-- The intent here is to list all potential root causes and corrective actions to help investigating your own issues.''
+  * **Low voltage power resistors R78 and R79** can get really hot and their solder joints are stressed a lot. Inspect these first.
+{{drawio>hotrod:r78r79.png}}
-==== Remove HotRod's back plate ====
+  * **Footswitch cricuit R97** is a good candidate too. Heats a lot.
+{{drawio>hotrod:r97.png}}
-Remove the 6 back screws and remove the back plate.
+  * Inspect all polarisation resistors in PCB, especially R4, R11, R16, R57, R58, R61, R62, and eventually power resistors R74 and R75.
-{{drawio>hotrod:back.png}}
+=== Capacitors ===
-Isn't it cute?
+  * power capacitors C31, C33, C35, C36, C40, C41 are large capacitors on which vibrations tend to stress solder joints. Inspect and rework them if needed.
-{{ :hotrod:pcb.png?nolink |}}
+{{drawio>hotrod:C40C41.png}}
-The first thing to do after every panel removal/power cycle is to check that power capacitors are properly soaked. Using a voltmeter on 300V+ setting, check that the residual voltage on SP1 is lower than 12V. If not, discharge C31 using a 50k-1W Resistor between its leads.
-{{drawio>hotrod:sp1test.png}}
+==== Apply solder paste on weakened tracks ====
+Strengthen damaged tracks/PCB with solder on tracks. In case a spot looks weakened (especially on critical heating components), consider creating solder tracks as shown :
+{{drawio>hotrod:soldertracks.png}}
+//Example of HotRod's 5W PSU resistors with strengthened copper tracks - Source Music Electronics Forum//
-====  ====
+Simply scratch the varnish over tracks using a sharp knife to reveal raw track copper, clean with alcohol/acetone, and then apply solder paste using iron.
+----
+===== Bugfix #4 - Replacing and strengthening PCB components =====
+The components listed in this section are worth replacing if any damage or sound issue is identified.
+There are some complete replacement kits avaiable on the internet, which include all components that are generally worth upgrading.
+==== Replace power capacitors ====
+If your main power capacitors are from the IC brand, generally shipped in light grey as shown below, they are low quality chinese capacitors which are prone to leak, seriously reducing amp performance.
+Consider replacing them with same value/voltage rating (FT, etc...).
+{{drawio>hotrod:changecap.png}}
+==== Replace burnt resistors ====
+Resistors R78 and R79 of the low voltage part are 5W 470 Ohms, but are exposed to transients up to 4.9W (48V@470Ohms). Upgrading these to higher quality 10W wired resistors is encouraged. Notably, installing the resistors slightly above PCB to increase air flow is recommended.
+{{drawio>hotrod:reschange.png}}
+----
+===== Bugfix #5 - Glue them all =====
+If not implemented, use RTV glue to fix large components, including all big capacitors.
+{{drawio>hotrod:glue.png}}
+Generally, medium sized capacitors from Power Supply are not glued and I suggest to glue them, because radial capacitors are sensitive to vibrations and this amp is really punchy.
+----
 ===== Resources: =====